Compound Et₂NCH₂CH₂N=C(Me)CH=C(Me)NHCH₂CH₂NEt₂ (HL), after conversion to the Li⁺ salt with use of MeLi, reacts with CuCl₂ in toluene to yield CuClL (1). The compound adopts a four-coordinate CuClN₃ environment with a pendant amino arm. The same reaction with CuCl and [Cu(MeCN)₄]BF₄ leads to disproportionation with deposition of metallic copper. Crystals of compounds [CuL][CuCl₂] (2) and [CuL]BF₄ (3) were isolated in minor amounts from these reactions. The [CuL]⁺ ion in these compounds has a four-coordinate CuN₄ environment. Compound 2 was also obtained in good yields from the reaction between equivalent amounts of 1 and CuCl. Compound 1 was used to control the radical polymerization of styrene under ARGET ATRP conditions in the presence of glucose as reducing agent and bromoethylbenzene as initiator. The polymerization behavior indicates that the controlling ability of this system is negatively affected by its slow trapping rate and by the disproportionation of the CuL catalyst.

The coordination chemistry of copper with a diamine-β-diketiminate ligand (a monoanionic N₄ donor) is explored in view ofdeveloping atom transfer radical polymerization with halogen-free Cu^I catalysts.

trans(Cl)-Ru(bpy)(CO)₂Cl₂ (1; bpy = 2,2′-bipyridine) was found to efficiently isomerize to cis(Cl)-1 in DMSO by addition of a catalytic amount of NaBH₄, even at room temperature. The isomerization reaction is air sensitive, but does not require photoirradiation. Addition of the Cl^– ion remarkably accelerates the reaction. A plausible chain reaction mechanism mediated by the reduced ruthenium dimer and monomer of 1 is proposed for the trans–cis isomerization.

The novel chain reaction for isomerization from trans(Cl) to cis(Cl)-Ru(bpy)(CO)₂Cl₂, which is induced by a catalytic amount of NaBH₄ and proceeds smoothly even at room temperature, is reported. This chain isomerization is a rare reduction-triggered trans–cis isomerization, which is a promising methodology that produces the cis-ruthenium mono(bipyridine) derivatives under moderate conditions.

Dimethyl acetylenedicarboxylate reacts with 2 mol-equv. B(C₆F₅)₃ by C₆F₅ transfer to the central acetylenic C≡C bond with formation of a tail-to-tail coupled bis(boron ester enolate) system. The central hexasubstituted butadiene unit of this unique system reacts with dimethyl maleate in a Diels–Alder reaction to give a hydroquinone derivative.

Dimethyl acetylenedicarboxylate reacts with 2 mol-equiv. B(C₆F₅)₃ by C₆F₅ transfer to the central acetylenic C≡C bond with formation of a tail-to-tail coupled bis(boron ester enolate) system. The centralhexasubstituted butadiene unit of this unique system reacts with dimethyl maleate in a Diels–Alder reaction to give a hydroquinone derivative.

A beltlike V₂O₃@C core–shell-structured composite was successfully synthesized by thermal treatment with the precursor V₃O₇·H₂O@C composite under an inert atmosphere. The phase, composition, structure, and morphology of the as-obtained samples were confirmed by XRD, elemental analysis, FTIR, energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), IR Raman, SEM, and TEM measurements. The process of the formation of V₂O₃@C is briefly discussed. The carbon coated onto the surface of V₂O₃ is disordered, and V₂O₃ keeps the original morphology of V₃O₇·H₂O. V₂O₃@C has an average length that ranges from 0.4 to 5.2 μm, a width of about 80–170 nm, and an average thickness of the shells of about 15.6 nm. The possible formation mechanism of V₂O₃@C is proposed as follows: the reaction undergoes a solid-state reaction by the interface reaction between V₃O₇ cores and carbon shells. It was found that the V₂O₃@C composite possesses the same phase-transition properties as V₂O₃, which could expand the possible applications of materials related to V₂O₃ in the future. Furthermore, a V₂O₃ sphere, a V₂O₃ nanobelt, and the beltlike V₂O₃@C composite were explored as cathode materials for application in lithium-ion batteries. The beltlike V₂O₃@C composite electrode exhibited the best electrochemical properties among them, thereby achieving our aim of improving the electrochemical properties of V₂O₃.

We have fabricated a V₂O₃@C core–shell-structured composite by using the precursor V₃O₇·H₂O@C and examined the discharge capacity versus the cycle number curves for a V₂O₃ sphere, a V₂O₃ nanobelt, and the V₂O₃@C composite.

Using [Ln(L)₈]³⁺ [Ln = Tb, Y; L = dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF)] cations as templating reagents, the syntheses and crystal structures of the following new metal organic–inorganic hybrid complexes based on either discrete clusters or 1D chains of an iodoplumbate or -bismuthate moiety are reported: [Tb(DMSO)₈]₂[(DMSO)₂Pb₅I₁₆] (1), [Tb(DMF)₈][Pb₃I₉]_1∞·DMF (2) and [Ln(DMF)₈][Bi₂I₉] [Ln = Y (3), Tb (4)]. These derivatives were characterized by thermogravimetric analysis (TGA), diffuse-reflectance spectroscopy, luminescence spectroscopy and magnetic studies. TGA studies show that the thermal stability of these complexes decreases in the order 2 > 3 ≈ 4 > 1. An optical band-gap in the range 1.90–2.15 eV in the diffuse-reflectance spectra of 1–4 indicate their potential use as semiconductors, 3 and 4 being the most promising because of their low band gap values. Compared to the precursors [Tb(DMSO)₈]I₃ and [Tb(DMF)₈]I₃, the high energy transitions in the excitation spectra of 1, 2 and 4 are quenched by a process that is best attributed to the autoionization of the carriers in the material. The temperature dependence of the magnetic susceptibilities of 1, 2 and 4 was reproduced well by a Curie–Weiss plot at 2–300 K.

New hybrid complexes composed of metal–organic cations with a magnetic/luminescent terbium centre and iodometallate anions derived from the neutral semiconductor PbI₂ and BiI₃ are reported, and the solvent-induced interconversion among the iodoplumbate derivatives is described.

The interaction of the negatively charged Ln³⁺ chelate Ln–DOTP with β- and γ-cyclodextrins bearing ammonium groups at the upper rim (CD⁺s) was investigated using mass spectrometry and NMR spectroscopic techniques. Mass spectroscopy shows the presence of 1:1 adducts of Ln–DOTP and both β- or γ-CD⁺. The peak intensities increased upon increasing the pH of the samples from 7 to 9.0, suggesting an increase in the strength of the interaction. Lanthanide induced ¹H NMR chemical shifts and relaxation ratesmeasured in aqueous solutions confirmed the presence of these adducts. The strength of the interactions appeared to be dependent on the pH, reflecting the strong electrostatic interactions between the oppositely charged host CD⁺ and guest Ln–DOTP chelate. Evaluation of the lanthanide induced relaxation rates showed that the Ln–DOTP does not enter the cavity of the CDs, but remains above it with a distance of 10–11 Å between the Ln³⁺ ion and the centre of the CD. Molecular modelling indicated that hydrogen bonds between the functionalized groups participating in the interaction sites contribute to the adduct stabilization. The apparent binding constants at pH 7 and 9 were obtained by using relaxometric measurements at 9 MHz. Fitting the NMRD profiles showed an increase in the number of second-sphere water molecules surrounding the phosphonate pendant arms of the Ln–DOTP chelate upon its interaction with the CDs. A brief description of the PARACEST properties of the supramolecular systems formed by Tm–DOTP and the positively charged CDs is presented. Both CDs display a shift of the saturation transfer peaks of the ammonium functions by the Tm complex, with an accentuated effect observed for the γ-CD derivative.

The negatively charged Ln–DOTP chelate forms relatively strong 1:1 supramolecular adducts with β- and γ-cyclodextrins bearing ammonium groups at the upper rim. The strength of the host–guest interaction depends on the pH. The geometry of the adducts, obtained from paramagnetic shift and relaxation effects, shows that the host is outside the guest cavity.

Microwave-assisted synthesis represents a valuable improvement in the domains of molecular and organic chemistry and was recently extended to inorganic and materials chemistry. A comparison of titanium dioxide nanoparticles synthesised in aqueous solution prepared in a microwave or a conventional oven is presented here. More precisely, three different protocols were used in order to determine the impact of the heating mode on the final product in terms of crystalline structure, particle size and morphology. Therefore, the resultant powders were analysed by Raman spectroscopy as well as X-ray and electron diffraction and transmission electron microscopy. The results show that microwave treatment significantly reduces the heating time and generally produces smaller nanoparticles. The rutile/anatase/brookite phase distribution is also modified by the heating mode in certain protocols up to the formation of a pure anatase phase, for instance. The impact of microwaves on the solvent and on the inorganic precursors has been demonstrated. A photocatalytic test and time-resolved microwave conductivity experiments were performed on rather similar samples prepared with the two heating modes in order to probe the improvement of the crystalline quality and its consequences on the photocatalytic activity of the TiO₂ material.

In the present study of TiO₂ nanomaterials elaborated in aqueous conditions, it is demonstrated that microwave-assisted synthesis may significantly change the structure and size of nanoparticles in comparison with conventional heating although it does not systematically improve the targeted property.

The reactivity of Pd complexes having bidentate diarylphosphane ligands was studied in the oxidative carbonylation of CH₃OH to dimethyl carbonate/oxalate (DMC/O) with PhNO₂ as the oxidant. Different ligands were employed with variation in backbone length and aryl ring substituent, and the acidity, CO pressure, or the partial pressure of H₂ was varied. At two different stages in the catalytic cycle, one equivalent of DMC/O may evolve for every equivalent of PhNO₂ reduced, which means that the efficiency with which nitrobenzene can function as the oxidant for the oxidative carbonylation of methanol (E_OC) can potentially be 200 % relative to nitrobenzene conversion. The selectivity for DMC relative to DMO is thought to be determined by a species of the type [P₂PdC(O)OCH₃(R)]; the DMO/DMC ratio can be increased by increasing the CO pressure, by addition of an acid, or by using a ligand with a relatively large bite angle. On the basis of the collected results, we conclude that an ideal catalyst for oxidative carbonylation would have a relatively acidic palladium center and be sterically undemanding in the axial positions but sterically demanding in the equatorial positions of palladium. The Pd complex of bis(diphenylphosphanyl)ferrocene meets these criteria and was found to function most efficiently with PhNO₂ as oxidant for the oxidative carbonylation of methanol among the series of compounds studied, that is, with about 50 % of the theoretical maximum efficiency E_OC.

The catalytic reactivity of palladium complexes having bidentate diarylphosphane ligands was studied in the oxidativecarbonylation of methanol to dimethylcarbonate (DMC) and dimethyl oxalate (DMO) with nitrobenzene as terminal oxidant. Nitrobenzene can be reduced to aniline by the hydrogen atoms liberated, and thus a catalytic coupling between methanol oxidation and nitrobenzene hydrogenation is established.

The influence of 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-butyl-1-methylpyrrolidinium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate and 3-(2-hydroxyethyl)-1-methylimidazolium tetrafluoroborate ionic liquids (ILs) on the morphology and structure of CaCO₃ has been investigated in an ethanolic medium by using calcium chloride and ammonium carbonate as the calcium and carbon sources, respectively. Syntheses were carried out at 9 °C and room temp. at different IL concentrations and CO₃^2–/Ca²⁺ molar ratios. No polymorph selectivity was detected, and calcite was the sole crystalline form obtained under all the considered reactions conditions. In the case of the BF₄^–-based ILs, anion decomposition occurred, which led to the formation of fluorite. Low temperature reduced the precipitation rate. With the ILs employed, the morphology of CaCO₃ has been finely tailored: calcite microcubes, microframes and microboxes with potential application in drug delivery, as well as nanocubes and nanocorn-like objects were produced with Cl^–-based ILs; with BF₄^–-based ILs, hierarchically structured materials, in which calcite coexists with fluorite, and complex and intricate shapes were produced, such as nanostructured microspheres, nanostructured calla-lily-like and ice-cream-ball-like micro-objects.

CaCO₃ was precipitated in ethanol by using calcium chloride, ammonium carbonate and an ionic liquid (IL). With Cl^–-based ILs, calcite microcubes, microframes, microboxes, nanocubes and nanocorn-like objects were obtained. With BF₄^–-based ILs, calcite and fluorite nanostructured microspheres, nanostructured calla-lily-like and ice-cream-ball-like micro-objects were produced.

The change in the environment around Eu³⁺ and Eu²⁺ species as a function of their concentration in BaSnO₃:Eu nanomaterials has been investigated by low-temperature (77 K) luminescence and electron paramagnetic resonance (EPR) spectroscopy. These materials show dual emission from the europium ions upon single-wavelength excitation. Europium ions (Eu³⁺ and Eu²⁺) occupy the centrosymmetric Ba²⁺ sites up to 4 atom-% in BaSnO₃, beyond which it forms a separate europium oxide phase with both Eu²⁺ and Eu³⁺ ions. There is energy transfer from the BaSnO₃ host to the Eu²⁺ ions in the samples. Upon single-wavelength UV excitation (280 nm) of the BaSnO₃:Eu nanomaterials, strong emissions at 430, 480, 590 and 612 nm, characteristic of exciton recombination in the host BaSnO₃ (430 nm), the 4f⁶5d¹(T_2g)→4f ⁷(⁸S_7/2) transition of Eu²⁺ (480 nm) and intra-4f transitions of Eu³⁺ (590 and 612 nm) have been observed. For samples that contain more than 4 atom-% europium ions based on steady-state luminescence measurements and lifetime values that correspond to the ⁵D₀ level of Eu³⁺ ions, it is inferred that there are mainly three types of Eu³⁺ ions: the first at Ba²⁺ sites with perfect dodecahedral geometry in the bulk of the nanomaterials, the second at Ba²⁺ sites at the surface of the nanomaterials and the third type as a separate europium oxide phase. Similarly, EPR specroscopy confirms the presence of three types of environments for the Eu²⁺ species.

The incorporation of Eu³⁺ ions at Ba²⁺ sites in BaSnO₃ generates cation vacancies in the lattice. The electrons present in some of the cation vacancies reduce Eu³⁺ to Eu²⁺ at the Ba²⁺ sites. Hence, at any instant, the BaSnO₃ lattice will contain cation vacancies along with Eu³⁺ and Eu²⁺ ions occupying the Ba²⁺ sites, which leads to dual luminescence from the Eu ions.

This paper shows how supporting the Dawson heteropoly compound (HPC) (NH₄)₆P₂Mo₁₈O₆₂ opens up the possibility to enhance its catalytic activity by controlling its molecular behaviour. The effect of parameters such as the loading of the Dawson species onto a support and the nature of its interaction is explored by IR and Raman spectroscopy and correlated with its performance in the oxidation of propene. Active species in propene oxidation were formed during the Dawson HPC rearrangement occurring on a TiO₂ support. When supported, the Dawson (NH₄)₆P₂Mo₁₈O₆₂ HPC is beneficially activated during the catalytic process, which led to the formation of a supported active species. A conversion stability observed for the HPC/TiO₂ samples with loading above 5 wt.-% revealed that the Dawson HPC had to interact with the support to develop a stable activity. This arrangement seemed indeed to be the most suitable to reach a high conversion. On the contrary, it was proposed that isolated HPC species were more prone to destabilization due to the loss of the proximity between the anions in the HPC crystal lattice. This work will show that the catalytic systems operated very efficiently due to the redox properties of molybdenum atoms when in an HPC 3D framework. This could not have happened with low loadings as only fragments of the HPCs were present on the surface. The stabilization of catalytic activities observed in the supported catalysts with high loadings was associated with the stabilization of a Keggin-like supported phase.

This paper shows how supporting the Dawson (NH₄)₆P₂Mo₁₈O₆₂ heteropoly compound opens up the possibility to enhance its activity in propene oxidation by controlling its molecular behaviour. The effect of parameters such as the loading of the Dawson species onto a support and the nature of its interaction is correlated with its performance.

We synthesized manganese oxide (MnO and Mn₃O₄) nanocrystals with various sizes and shapes by the thermal reaction of a Mn^II–oleate complex through a “heat-up process”. When a Mn^II–oleate complex was thermally decomposed in non-coordinating hydrocarbon solvents, uniformly sized MnO nanocrystals with cubic and octahedral shapes were produced. We were able to synthesize anisotropic, multibranched MnO nanocrystals by the oriented attachment of MnO truncated-nanocube building blocks. When the Mn^II–oleate complex was heated in 1-hexadecene in the presence of strongly coordinating carboxylic acid surfactants, spherical nanocrystals were generated, and their diameter was controlled in the range 3–13 nm by varying the chain length of the carboxylic acid. When oleyl alcohol was added to the Mn–oleate complex in phenyl ether, tetrahedral MnO nanocrystals were synthesized. The as-synthesized MnO nanocrystals were oxidized in air to Mn₃O₄ or MnO/Mn₃O₄ core–shell structures, which exhibited exchange coupling with shifted magnetic hysteresis loops. The effect of the size and shape of the phospholipid-capped manganese oxide nanocrystals on their applicability as T₁ contrast agents in magnetic resonance imaging (MRI) were examined. As the size of the nanocrystals decreased, their relaxivities increased, thereby generating brighter MR images. In particular, spherical 3 nm-sized Mn₃O₄ nanocrystals had a high specific relaxivity (r₁) of 2.38 mM^–1 s^–1, clearly demonstrating their potential for use as an efficient T₁ MRI contrast agent.

Manganese oxide nanocrystals with various sizes and shapes were synthesized by thermal decomposition of a Mn–oleate complex. The effect of the size and shape of the phospholipid-capped nanocrystals on their applicability as T₁ contrast agents in magnetic resonance imaging (MRI) was examined. As their size decreased, their specific relaxivities increased, which generated brighter MR images.

The synthesis and characterization of four new DOTA-tetraamide ligands having variable alkyl chain lengths (C₁, C₁₂, C₁₄, and C₁₆) and their respective europium(III) complexes are reported. The three EuL complexes having long alkyl chains spontaneously form micelles of variable size. The critical micelle concentration differed for each complex (lower for the C₁₆ complex than the C₁₂ complex) while micelle size increased with increasing alkyl chain length. Chemical exchange saturation transfer (CEST) experiments showed that all four Eu^III complexes displayed slow-to-intermediate water exchange kinetics. As expected, the CEST signals in these complexes decreased with increasing temperatures due to faster water exchange but, interestingly, the CEST signals for the C₁₄ and C₁₆ complexes approached a maximum near 25 °C consistent with exchange limited CEST at or near room temperature. The water residence lifetimes obtained by fitting the CEST spectra to the Bloch equations increased in parallel with an increase in alkyl carbon chain-length. By comparisons with the monomethylamide complex, which served as control, the data illustrate that micelle formation serves to slow the rate of water exchange in these systems. The complex having the largest CEST effect per unit Eu^III concentration (the C₁₆ analog) had a detection limit of 5.3 μM. This represents an approximate 250-fold increase in sensitivity relative to the monomethylamide control (detection limit ≈ 1.3 mM). These features highlight the potential of using micelle-based systems such as these as paramagnetic chemical exchange saturation transfer (PARACEST) agents for molecular imaging by MRI.

Four new EuDOTA-tetraamides with variable alkyl chains lengths were synthesized and their CEST properties were extensively studied. Three of these complexes werefound to spontaneously form micelles due to their long alkyl chains which resulted in a dramatic increase in their CEST sensitivities.

Substitution of the aromatic hydrogen atoms in the electron donors 1,2,4,5-tetrakis(tetramethylguanidino)benzene (1a) and 1,2,4,5-tetrakis(N,N′-dimethyl-N,N′-ethyleneguanidino)benzene (1b) by iodide (to give 2a and 2b) and nitro groups (to give 3a and 3b) afforded new redox-active ligands. Their properties (electron donor capacity, Brønsted basicity and optical spectra) have been analyzed and compared with the unsubstituted 1,2,4,5-tetrakis(guanidino)benzenes. The experimental results are supplemented by quantum chemical calculations. The first late-transition metal complex of the push–pull ligand 3a was prepared and characterized and its oxidation studied.

The properties of redox-active guanidino-functionalized aromatic ligands, such as the HOMO–LUMO gap and the electron donor capacity, could be modified over a large range by substitution at the aromatic ring.

Mn²⁺ has five unpaired d electrons, a long electronic relaxation time, and labile water exchange, which make it an attractive alternative to Gd³⁺ in the design of contrast agents for medical Magnetic Resonance Imaging. In order to ensure in vivo safety and high contrast agent efficiency, the Mn²⁺ ion has to be chelated by a ligand that provides high thermodynamic stability and kinetic inertness of the complex and has to have at least one free coordination site for a water molecule. Unfortunately, these two requirements are contradictory, as lower denticity of the ligands, which leads to more inner-sphere water molecules often implies a decreased stability of the complex, and, therefore, it is necessary to find a balance between both requirements. In the last decade, a large amount of experimental data has been collected to characterize the physico-chemical properties of Mn²⁺ chelates with variable ligand structures. They now allow for establishing trends of how the ligand structure, the rigidity of the ligand scaffold, and its donor–acceptor properties influence the thermodynamic, kinetic, and redox stability of the Mn²⁺ complex. This microreview surveys the current literature in this field.

Mn²⁺ chelates are interesting candidates for application as MRI contrast agents. In the design of novel ligands for Mn²⁺ complexation, one has to find a balance between good thermodynamic stability and high efficiency (relaxivity) of the complex.

A series of allyl 1,2,3-triazol-5-ylidene (tzNHC) palladium complexes was prepared, and the structures of the complexes were fully characterized by NMR and X-ray diffraction analyses. The donor properties of these ligands were evaluated by studying the vibrational spectra of their carbonyliridium complexes and their X-ray photoelectron spectra. These evaluations showed that the structures of the tzNHC palladium complexes are almost identical to those of the corresponding imidazole carbene palladium complexes, and that the tzNHC ligands have stronger donor properties than the imidazole carbene ligands. The relationship between catalytic activity and structure was examined by carrying out a room-temperature Suzuki–Miyaura coupling reaction, and the cinnamylpalladium complex bearing 1,4-bis(2,6-diisopropylphenyl)-3-methyl-1,2,3-triazol-5-ylidene (TPr) was found to be the most active catalyst. (cinnamyl)(TPr)PdCl showed high activity in the room-temperature reaction performed with aryl chlorides regardless of the electronic and steric properties of the substituents, and was effective in reactions with sterically crowded arylboronic acids.

A series of (η³-allyl)palladium complexes bearing 1,2,3-triazole carbene (tzNHC) ligands has been prepared and characterized. The donor properties of tzNHC ligands are stronger than those of imidazole carbene ligands. The [1,4-bis(2,6-diisopropylphenyl)-3-methyl-1,2,3-triazol-5-ylidene](cinnamyl)PdCl complex shows high activity in the room-temperature Suzuki–Miyaura coupling reaction with aryl chlorides.

Four manganese-based carbazol-9-ylacetato complexes [Mn₂(cabo)₄(2,2′-bpy)₂] (1), [Mn₂(cabo)₂(2,2′-bpy)₄](ClO₄)₂ (2), [Mn(cabo)₂(CH₃OH)₂]_n (3), and [Mn(cabo)₂(4,4′-bpy)₂]_n (4) (cabo^– = carbazol-9-ylacetate, 2,2′-bpy = 2,2′-bipyridine, 4,4′-bpy = 4,4′-bipyridine) have been synthesized and characterized. The crystal structure of 1 consists of a symmetrical dimeric Mn^II carboxylato paddle-wheel unit, whereas dinuclear 2 consists of a dimeric unit with two Mn^II ions bridged by two carboxylato ligands. Compounds 3 and 4 present comparable 1D structures with Mn^II ions bridged by carboxylato ligands. Magnetic-property studies show that antiferromagnetic exchange interactions propagate among the Mn^II ions in 1, 2, and 3.

Four manganese-based carbazol-9-ylacetato (cabo) complexes with bipyridyl (bpy) as an ancillary ligand have been synthesized and their structures, and magneticproperties have been characterized. Antiferromagnetic exchange interactions propagate among the Mn^II ions.

The kinetic stabilities and relaxivities of a series of Eu²⁺-containing cryptates have been investigated. Transmetallation studies, which monitored the change in the longitudinal relaxation rate of water protons in the presence of Ca²⁺, Mg²⁺, and Zn²⁺, demonstrated that the cryptate structure influenced the stability, and two of the cryptates studied were inert to transmetallation in the presence of these endogenous ions. The efficacy of these cryptates was determined at different magnetic field strengths, temperatures, and pH values. Cryptate relaxivity was found to be higher at ultrahigh field strengths (7 and 9.4 T) relative to clinically relevant field strengths (1.4 and 3 T), but the efficiency of these cryptates decreased as the temperature increased. In addition, a variation in pH did not yield significant changes in the efficacy of the cryptates. These studies establish a foundation of important properties that are necessary to develop effective positive contrast agents for magnetic resonance imaging from Eu²⁺-containing cryptates.

Kinetic measurements showed that Eu²⁺-containing cryptates can be stable in the presence of Ca²⁺, Mg²⁺, and Zn²⁺ depending on the ligand structure. Relaxometric studies demonstrated that the efficiency of these cryptates is dependent on temperature but not on pH.

Bis(N-acylamidines) 1, which contain various rigid or flexible spacer units with different spatial orientations, are potent bis(bidentate) ligands for the coordination of metal ions. Treatment of 1 with Ni^II or Cu^II salts gave two 2:2 (3) and four 3:3 (4) metallomacrocycles by self-assembly. The structures of the hitherto unknown products were determined by the geometry of the ligands that incorporate either linear or bent spacers between the two binding sites. Complex 3b is especially interesting due to its two vinyl subunits orientated perpendicular to the plane of the molecule. Complexes 3 and 4 crystallize in planar layers with intercalated solvent molecules (N,N-dimethylformamide, dimethyl sulfoxide). The molecular structures of five coordination compounds in the solid state have been elucidated by X-ray diffraction.

Bis(N-acylamidines) are potent bidentate ligands that form 2:2 and 3:3 metallomacrocycles with nickel(II) and copper(II) by self-assembly. The nature of the coordination compounds is directed by the shapeof the spacer. Bent spacers give 2:2 complexes, whereas linear spacers lead to 3:3 macrocycles. Both types form layers in the solid state, which intercalate solvent molecules (DMF, DMSO).

The synthesis, structural characterization, electrochemistry and luminescence properties of a series of new yttrium and europium(+3) alkoxides bearing thiophene moieties are presented. The yttrium compounds were obtained by the reaction between Y[N(SiMe₃)₂]₃ and the tertiary alcohols HO–C(C₁₆H₁₃S) (2), HO–C(C₁₇H₁₅S) (3), HO–C(C₁₄H₁₁S₂) (4) and HO–C(C₁₆H₁₃S) (5) in thf or in a mixture of toluene and pyridine. The X-ray crystal diffraction measurements show a five-coordinated yttrium atom in distorted trigonal-bipyramidal geometry. The metal centres are surrounded by threemethoxido ligands in equatorial positions and two tetrahydrofuran [for {Y[OC(C₁₆H₁₃S)]₃(thf)₂}·toluene (8), {Y[OC(C₁₇H₁₅S)]₃(thf)₂}·toluene (10) and {Y[OC(C₁₄H₁₁S₂)]₃(thf)₂}·1/2 toluene (12)] or two pyridine [for {Y[OC(C₁₆H₁₃S)]₃(py)₂}·toluene (9) and {Y[OC(C₁₇H₁₅S)]₃(py)₂}·toluene (11)] molecules in axial positions. The compounds Y[OC(C₁₄H₁₁S₂)]₃(py)₂ (13) and Y[OC(C₁₆H₁₃S)]₃(py)₂ (14) were identified by NMR spectroscopy. In addition, a novel europium(+3) alkoxide {Eu[OC(C₄H₃S)₃]₃(thf)₃}·thf (15) was synthesized by the reaction between Eu[N(SiMe₃)₂]₃ and the tertiary alcohol HO–C(C₄H₃S)₃ (1) in thf. The molecular structure of this compound reveals an approximately octahedral coordination sphere around the europium(+3) metal centre with three methoxido ligands and three facially arranged tetrahydrofuran molecules. The cyclic voltammograms of the yttrium alkoxides indicate that the electrochemical properties are essentially dominated by the organic ligands. The electrochemical properties of {Eu[OC(C₄H₃S)₃]₃(thf)₃}·thf (15) are dominated by the oxidation of the thienyl moieties and in addition a reduction wave due to the reduction of Eu³⁺ to Eu²⁺ is visible. In comparison to the carbinols, the oxidation peak potentials of the thienyl units for the yttrium and europium(3+) alkoxides are marginally shifted towards higher values. The emission spectra of the carbinols and their derived yttrium compounds display broad bands attributed to the π*→π transitions of the aromatic ligands. Luminescence studies performed on compound 15 reveal the typical f–f transitions of the Eu³⁺ ions and suggest that an energy transfer from the ligand to the metal atom operates.

The reaction between a series of carbinols bearing thiophene and phenyl units and Ln[N(SiMe₃)₂]₃ (Ln = Y, Eu) in thf or a mixture of toluene and pyridine as solvent leads to the metal alkoxides: {Y[OC(C₁₆H₁₃S)]₃(thf)₂}·toluene, {Y[OC(C₁₆H₁₃S)]₃(py)₂}·toluene, {Y[OC(C₁₇H₁₅S)]₃(thf)₂}·toluene, {Y[OC(C₁₇H₁₅S)]₃(py)₂}·toluene, {Y[OC(C₁₄H₁₁S₂)]₃(thf)₂}·1/2 toluene, Y[OC(C₁₄H₁₁S₂)]₃(py)₂, Y[OC(C₁₆H₁₃S)]₃(py)₂ and {Eu[OC(C₄H₃S)₃]₃(thf)₃}·thf. The molecular structures of the compounds are reported and discussed. The physico-chemical studies of yttrium and europium(3+) alkoxides are also presented.

Two new discrete anionic species, [Cd₂Cl₇]^3– and [Cd₂Br₇]^3–, have been isolated in the form of cobalt(III) complex salts, [Co(phen)₃][Cd₂Cl₇]·3H₂O (1) and [Co(phen)₃][Cd₂Br₇]·2H₂O (2). The complex salts have been characterized by spectroscopic techniques and other investigations like TGA, solubility product measurements, conductance measurements, luminiscent study, DFT calculations and single crystal structure determinations. The new discrete [Cd₂X₇]^3– anions reside in cavities that are formed by complex cations and are stabilized by different noncovalent interactions (hydrogen bonding, π–π stacking, C–H···π and anion···π). With the help of DFT calculations, an in depth investigation has been conducted into what happens to the conformation of these anions in crystal, solution and gas phase, and the nature of the Cd–halogen bond has been elucidated.

Two new discrete anionic species, [Cd₂Cl₇]^3– and [Cd₂Br₇]^3–, have been isolated in the form of cobalt(III) complex salts. This successful isolation indicates the possibility of “caging” these ions with the help of a similarly sized and equally charged cation.

1-Acetyl- [1a; 3,5-CF₃, 1-C(=O)CH₃] and 1-benzoyl-5-hydroxypyrazolines [1b; 3,5-CF₃, 1-C(=O)C₆H₅] have been synthesized and treated with Ni(OAc)₂·4H₂O in the presence of an excess of base [NH₃ or 4-(dimethylamino)pyridine (DMAP)] to form the nickel complexes 4a–c. These complexes have been characterized by various techniques, which indicate a tridentate coordination mode of the ligands. X-ray crystallography determined an O,N,O′-coordination of the ligands, in which the ligand is planar, the oxygen donors are trans to each other, and the nitrogen donor is in a cis position. The other coordination sites on the nickel centre are occupied by the added base molecules (NH₃ or DMAP). The number of NH₃ or DMAP ligands depends on the nature of the base; in the case of ammonia, one molecule is coordinated to the nickel centre to form a diamagnetic square-planar complex, whereas with DMAP, an octahedral paramagnetic complex with three additional DMAP ligands was observed. Initial catalytic experiments have been performed by applying the complexes in the nickel-catalyzed C(sp²)–C(sp³) cross-coupling of aryl halides with benzylzinc bromides or dialkylzinc reagents; excellent yields and selectivities have been achieved.

New nickel complexes modified by versatile 5-hydroxypyrazoline ligands have been synthesized and characterized. The catalytic properties of the complexes have been investigated in nickel-catalyzed C(sp²)–C(sp³) cross-coupling reactions.

The protonation constants of DMPDTA (H₄DMPDTA = 2,2-dimethylpropylenediamine-N,N,N′,N′-tetraacetic acid) and the stability and protonation constants of its Ln³⁺ and some divalent metal complexes have been determined by pH potentiometry and spectrophotometry (Cu²⁺) and compared with the corresponding properties of the complexes formed with PDTA (H₄PDTA = propylenediamine-N,N,N′,N′-tetraacetic acid). The log K₂^H value of DMPDTA is lower by 1.5 log K units than that of PDTA. The stability constants (log K_ML) of the Ln³⁺ complexes formed with DMPDTA are lower by 1.0–1.5 log K units than those of PDTA. The kinetics of the transmetallation reactions of Gd(DMPDTA)^– and Gd(PDTA)^– with Cu²⁺ and Eu³⁺ have been studied by spectrophotometry. The reactions with Cu²⁺ and Eu³⁺ occur predominantly by spontaneous and proton-assisted dissociation of the Gd(DMPDTA)^– and Gd(PDTA)^– complexes. The rates of the metal-exchange reactions of Gd(DMPDTA)^– are significantly lower than those of Gd(PDTA)^–. The presence of the two methyl groups on the ligand backbone increases the kinetic inertness of Gd(DMPDTA)^– due to the higher conformational rigidity of DMPDTA. Temperature-dependent ¹⁷O NMR spectra and 1/T₁¹H nuclear magnetic relaxation dispersion profiles of the Gd³⁺ complexes were measured and analyzed to obtain the parameters that influence the water exchange rate and rotational dynamics.

The introduction of a gem-dimethyl group on the backbone of the ligand leads to a significant variation in the properties of the corresponding complexes, which originate from a different conformational behaviour.

A new cluster of formula {[Mo₃(μ₃-S)(μ-S)(μ-S₂)₂(dtp)₃(μ-OAc)][Mo₃NiS₄(dtp)₃(μ-OAc)(CH₃CN)]} (1; dtp = diethyl dithiophosphate; OAc = acetate) comprising the novel C_s-symmetrized Mo₃(μ₃-S)(μ-S)(μ-S₂)₂ structural type covalently attached to a cubane-type Mo₃NiS₄ core has been isolated and fully characterized. The reaction of a 2 M HCl solution of [Mo₃S₄(H₂O)₉]⁴⁺ with an excess of potassium diethyl dithiophosphate and acetic acid in the presence of the [Mo₃(NiCl)S₄(H₂O)₉]³⁺ cluster afforded a mixture of products encompassing different Mo₃S_x (x = 4–7) cluster cores from which the Mo₃(μ₃-S)(μ-S)(μ-S₂)₂ structural type has been isolated in analytically pure form as a Mo₃NiS₄ adduct. The robustness of the aggregate 1 was also retained in solution as judged by ESI-MS and ³¹P NMR techniques. Single-crystal X-ray analysis revealed in detail the complementary association of the newly formed Mo₃(μ₃-S)(μ-S)(μ-S₂)₂ entity and the Mo₃NiS₄ cluster in which μ-S sulfide ligands and μ-S₂ disulfide ligands act as nucleophilic and electrophilic functional groups, respectively, towards the Mo₃NiS₄ cube through directional Ni–S covalent bonds and short S···S contacts (below 3.3 Å).

A new cluster of formula {[Mo₃(μ₃-S)(μ-S)(μ-S₂)₂(dtp)₃(μ-OAc)][Mo₃NiS₄(dtp)₃(μ-OAc)(CH₃CN)]} (1; dtp = diethyl dithiophosphate; OAc = acetate) comprising thenovel C_s-symmetrized Mo₃(μ₃-S)(μ-S)(μ-S₂)₂ structural type covalently attached to a cubane-type Mo₃NiS₄ core has been isolated and fully characterized.

Sodium hexaniobate (Na₇[HNb₆O₁₉]·15H₂O) was synthesized by a one-pot sol–gel method at room temperature by using an immiscible, biphasic solution. An organic solution was prepared by dissolving niobium pentaethoxide [Nb(OC₂H₅)₅] in ethanol, which was then added to hexane. This solution was brought into contact with an aqueous NaOH solution to form a reaction system consisting of two separate phases. A white precipitate was formed within 12 h at the bottom of the aqueous solution. It exhibited well-defined rod-like morphology on a micrometer scale. A comparative study was performed on the basis of a single-phase solution by mixing Nb(OC₂H₅)₅ in ethanol and the aqueous NaOH solution. The results indicated that the product formed by way of the single-phase solution was rather different in morphology from that obtained in the biphasic system. In both cases, Na₇[HNb₆O₁₉]·15H₂O could be converted to NaNbO₃ by heating at 600 °C. Mechanisms underlying the formation of Na₇[HNb₆O₁₉]·15H₂O and its conversion to NaNbO₃ are discussed on the basis of the experimental results.

Rod-like sodium hexaniobate particles were synthesized by a one-pot sol–gelmethod at room temperature by using an immiscible hexane–water system. They could be converted into NaNbO₃ by a heat treatment and a water dispersion treatment.

MnF₂ nanorod assemblies in a pompon-like fashion were synthesized by using a new complex, Mn(hfa)₂·tmeda [(Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentandione, tmeda = N,N,N′,N′-tetramethylethylenediamine)]. The complex was synthesized in a single-step reaction, and single-crystal X-ray diffraction studies provide evidence of a mononuclear structure. The thermal analyses have shown that the complex is thermally stable and can be evaporated to leave less than 2 % residue at atmospheric pressure. On the basis of its thermal properties, it has been successfully applied to the atmospheric pressure metalorganic chemical vapor deposition (AP-MOCVD) of MnF₂ nanostructures.

A mild approach, atmospheric pressure metalorganic chemical vapor deposition (AP-MOCVD), was applied for the fabrication of pompon-like assemblies of MnF₂ nanorods. Mn(hfa)₂·tmeda [(Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentandione, tmeda = N,N,N′,N′-tetramethylethylenediamine)] was used as a single-source precursor.

Very small ruthenium and platinum nanoparticles have been prepared from organometallic complexes by using 1,3,5-triaza-7-phosphaadamantane (PTA) as stabilizer, which allowed their easy dispersion into water. These nanoparticles were fully characterized by different techniques. In particular, the coordination of PTA to the surfaces of the particles was studied by NMR spectroscopy. The potential of these nanoparticles as catalysts was investigated in aqueous biphasic catalysis; olefins and arene derivatives were hydrogenated under mild conditions of temperature and pressure with interesting conversions and selectivities despite the change of environment they underwent after their dissolution in water.

PTA-stabilized ruthenium and platinum nanoparticles prepared from organometallic precursors display interesting catalytic reactivity in aqueous biphasic hydrogenation catalysis under mild conditions. The coordination of PTA to the surfaces of the particles was investigated by NMR spectroscopy as it governs the characteristics of the particles as they disperse into water.

The synthesis of metal oxide nanosheets using a lamellar phase as a template effectively modified the nanosheets because surfactant molecules surround the entire surface of the nanosheets. Here, we show the development of layered titanate nanosheets with a lamellar mesostructure. The layered titanate nanosheet forms by using the lamellar self-assembly of cationic dodecanediamine as a template and an electrostatic interaction between negatively charged titanate nanosheets and positively charged 1,12-dodecanediamine during hydrothermal synthesis. This approach leads to titanate nanosheets with new properties such as visible light absorption and a high adsorption of cationic organic compounds, which results in the effective photodegradation of Rhodamine B under visible-light irradiation. This approach has important implications for the use of metal oxide nanosheets in environmental and industrial applications.

Layered titanate nanosheets with a lamellar mesostructure were synthesized using lamellar self-assembly as a template. Effective surface modification of the nanosheets led to visible light absorption and high adsorption of cationic organic compounds, which led to the effective photodegradation of Rhodamine B under visible-light irradiation.

Magnetic resonance imaging (MRI) contrast agents represent a worldwide billion-dollar market annually. While T₁ relaxivity enhancement contrast agents receive greater attention and a significantly larger market share, the commercial potential for T₂ relaxivity enhancing contrast agents remains a viable diagnostic option because of their increased relaxivity at high field strengths. Improvement of the contrast and biocompatibility of T₂ MRI probes may enable new diagnostic prospects for MRI. Paramagnetic lanthanides have the potential to decrease T₁ and T₂ proton relaxation times, but are not commercially used in MRI diagnostics as T₂ agents. In this article, oxygen donor chelates (hydroxypyridinone, HOPO, and terephthalamide, TAM) of various lanthanides are demonstrated as biocompatible macromolecular dendrimer conjugates for the development of T₂ MRI probes. These conjugates have relaxivities of up to 374 mM^–1 s^–1 per dendrimer, high bioavailability, and low in vitro toxicity.

The development of high relaxivity andbiofunctional MRI probes is essential to increasing clinical diagnostic ability. T₂ MRI probes using lanthanides have the potential to increase relaxivity, biocompatibility, and offer the prospective to increase imaging modality functions.

Two multiligand coordination compounds, [Mn(AZT)₄(H₂O)₂](PA)₂·4H₂O (1) and [Co(AZT)₂(H₂O)₄](PA)₂ (2), were synthesized with 3-azido-1,2,4-triazole (AZT) as a ligand and picrate (PA) as a counteranion and characterized by elemental analysis and FTIR spectroscopy. The crystal structures were determined by single-crystal X-ray diffraction. The results show that the crystals of 1 and 2 have a triclinic space group (P) and orthorhombic space group (Pbca), respectively. Moreover, 1 and 2 have distorted octahedral structures. Their thermal decomposition mechanisms were investigated by differential scanning calorimetry and thermogravimetric analysis. The experimental data showed that the energies of combustion were approximately equal to the energies of combustion of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetraazocane (HMX). The nonisothermal kinetic parameters were studied by applying the methods of Kissinger and Ozawa. The sensitivity properties showed that 1 and 2 had a higher flame sensitivity than 2,4,6-trinitrotoluene, RDX, and HMX.

The structure of [Co(AZT)₂(H₂O)₄](PA)₂ (AZT = 3-azido-1,2,4-triazole, PA = picrate) shows that the Co^II ion is six-coordinate in a slightly distorted octahedral geometry. The energy of combustion and enthalpy of formation are 8.83 MJ kg^–1 and –3419.53 kJ mol^–1, respectively. Nonisothermal kinetic analysis indicated that the Arrhenius equation can be expressed as ln k = 15.23 – 153.3 × 10³/(RT).

When working with chemical solution deposition techniques, one of the main issues for optimal performance of CeO₂ buffer layers in coated conductors is the insufficient chemical stability of the CeO₂ layer during YBa₂Cu₃O₇ (YBCO) thermal processing. This work focusses on the morphology and nanostructure in thin CeO₂ films prepared by means of a novel aqueous synthesis route and incorporated into a Ni–W/La₂Zr₂O₇/CeO₂/YBa₂Cu₃O₇-coated conductor. Optimization of precursor chemistry and thermal processing led to a reduction in barium cerate formation. In a new precursor design, iminodiacetic acid was used as a stabilizing ligand, which resulted in an improved morphology of the buffer layer. A shelf life of more than 6 months was established by using a metal-to-ligand ratio of 1 to 5. During thermal processing, a combination of a slow calcination ramp with a high sintering ramp, short sintering dwell time and a low oxygen partial pressure during the synthesis resulted in a root mean square roughness below 3 nm for AFM analysis, a [111] to [002] ratio of 1 to 90 in X-ray diffraction and well-defined patterns in reflection high-energy electron diffraction (RHEED) analysis of the CeO₂ surface. Trifluoroacetate-YBCO was deposited on top of the CeO₂ buffer layer. Cross-section analysis with a focussed ion beam allowed us to correlate the morphology and nanostructure of the CeO₂ buffer layer with the formation of BaCeO₃ and the appearance of voids and secondary phases throughout the YBa₂Cu₃O₇ layer.

Smooth, well-textured CeO₂ buffer layers for coated conductors were synthesized by aqueous precursor formulations. The texture and morphology were characterized. Deposition of YBa₂Cu₃O₇ (YBCO) by metal–organic deposition with trifluoroacetate (TFA-MOD) and focussed ion beam analysis allowed the characterization of YBCO and the growth of secondary phases as a function of properties of the buffer layer.

A series of one-dimensional heterotrimetallic assemblies, [Cu₂Ln(L)₂(H₂O)₄][M(CN)₆]·nH₂O [Ln = Gd, M = Co (1), Fe (2), Cr (3), and Ln = La, M = Co (4), Fe (5), Cr (6)], were prepared by the reaction of a Cu₂Ln precursor complex, [Cu₂Ln(L)₂(NO₃)₃], with K₃[M(CN)₆] in water. All of the assemblies were isomorphous and formed a 1D zigzag chain, in which the [Cu₂Ln(L)₂(H₂O)₄]³⁺ and [M(CN)₆]^3– units were alternately positioned and were linked in a Cu–NC–M–CN–Cu manner. Compound 1 showed magnetic behaviour similar to that of the discrete precursor complex, [Cu₂Gd(L)₂(NO₃)₃], owing to the diamagnetic nature of the [Co^III(CN)₆]^3– unit. In the case of 2, a simple summation of the magnetic behaviour of the [Cu₂Gd(L)₂(H₂O)₄]³⁺ and [Fe(CN)₆]^3– units was observed, whereas ferromagnetic interactions were found to be operative between the Cu²⁺ and Cr³⁺ ions in compound 3. The same magnetic interactions between Cu²⁺ and M³⁺ were confirmed in compounds 4 to 6, which included the diamagnetic La³⁺ ion. The differences in the magnetic behaviours of 2 and 3 can be explained by the overlap of the d(Cu)–pπ(CN) orbitals in the bent Cu–N≡C linkage and the spin-density on the cyanide nitrogen of the [Cr(CN)₆]^3– unit.

Novel cyanide-bridged assemblies that have ordered alternate arrays of three types of paramagnetic metal centres were obtained from the reaction of preorganized heterobimetallic trinuclear complexes, [Cu₂Ln(L)₂(NO₃)₃] (Ln^III = Gd, La) and K₃[M(CN)₆] (M^III = Co, Fe, Cr). These form a 1D zigzag chain that is extended by the M^III–CN–Cu^II linkages and exhibit different magnetic behaviour, which depends on the combination of the metal ions.

Visible-light-responsive photonic structures have been prepared in alcohol solvents by using silica-modified PbS colloidal nanocrystal clusters (CNCs) as building blocks. Further modification of the PbS CNCs with a coating of silica allowed the dispersion of the particles into nonaqueous solutions. Repulsive electrostatic and solvation forces contribute to the self-assembly of the PbS@SiO₂ spheres. The core–shell particles have optical properties similar to those of CNCs, and they can also be assembled into close-packing films through simple drop-casting on silicon substrates. Embedding droplets of such a PbS@SiO₂ colloidal solution in a polymer matrix produced solid composite materials with visible-light-responsive optical properties with potential applications as sensors and optical switches.

Visible-light-responsive photonic structures have been prepared in alcohol solvents by using silica-modified PbS colloidal nanocrystal clusters as building blocks. Repulsive electrostatic and solvation forces contribute to the self-assembly of the PbS@SiO₂ spheres. Solid polymer composite films with similar light-responsive optical properties have also been produced in polymer matrices.

The new compound [Co(tren)(trenH₂)]₂[{Co(tren)}₂V₁₅Ge₆O₄₂S₆(H₂O)]·9H₂O [1, tren = tris(2-aminoethyl)amine] has been obtained under solvothermal conditions and features the unique thiogermanatovanadatopolyoxoanion[V^IV₁₅Ge^IV₆O₄₂S₆(H₂O)]^12– as the main structural motif. Compound 1 crystallizes in the monoclinic space group P2₁/c with a = 15.4711(2), b = 26.4031(4), c = 26.7213(4) Å, V = 10874.2(3) ų, and Z = 4. The [V₁₅Ge₆O₄₂S₆(H₂O)]^12– cluster anion displays the spin topology reported for the molecular magnets [V^IV₁₅As^III₆O₄₂(H₂O)]^6– and [V^IV₁₅Sb^III₆O₄₂]^6– and therefore represents a new member of the {V₁₅E₆} family, which has allowed us to study the magnetic exchange interactions between the vanadyl (d¹) groups of the geometrically frustrated central V₃ triangle, which is sandwiched between strongly antiferromagnetically coupled V₆ hexagons. The cluster shell is expanded by two {Co(tren)}²⁺-based complexes through Co–S bonds, which reduce the high negative charge of the anion. The Co²⁺ ions in the [Co(tren)(trenH₂)]⁴⁺ countercations are coordinated to one tetradentate tren and a monodentate, doubly protonated tren ligand.

The new polyoxovanadate [{Co(tren)}₂V₁₅Ge₆O₄₂S₆(H₂O)]^8– was directly synthesized from vanadate and elemental Ge and S. The cluster core [V₁₅Ge₆O₄₂S₆(H₂O)]^12– is the first V–Ge–O–S cluster and features the spin topology of the seminal molecular magnet [V₁₅As₆O₄₂(H₂O)]^6–. The cluster anion is expanded by sulfur-bound, pentacoordinate Co²⁺ complexes.

Zinc dichloride and dimethylzinc were treated with several acyclic and bicyclic guanidines. Three different bicyclic guanidines and their potassium guanidinate salts were treated with ZnCl₂. The reaction with the neutral guanidines afforded mononuclear complexes, stabilized by intramolecular hydrogen bonding. The reaction with the potassium guanidinate salts led to trinuclear complexes, which were extremely water sensitive. The reaction in the presence of added water furnished a tetranuclear complex with a central OZn₄ unit in good yield, to which six guanidinate ligands were bound. The reaction of dimethylzinc with 2-[N,N′-diisopropylguanidino]pyridine and 2-[N,N′-diisopropylguanidino]quinoline afforded di- and tetranuclear Zn methyl complexes with mono- and dianionic guanidinate ligands. Dinuclear complexes of the monoanionic guanidinate ligands were formed at room temperature. At higher temperatures (75 °C), complete deprotonation of the guanidino groups and formation of tetranuclear Zn alkyl complexes was observed, which feature low-coordinate zinc sites.

Bicyclic and acyclic guanidinate ligands stabilize several new oligonuclear zinc complexes.

The interaction of the VO²⁺ ion with pyrone derivatives and tropolone, which form very effective antidiabetic compounds, is critically re-examined. The binary systems with ethylmaltol (Hema) and tropolone (Htrop) were studied in aqueous solution and in the solid state through the combined application of spectroscopic (EPR, UV/Vis and IR) and pH-potentiometric techniques. The results were compared with those of the systems with maltol (Hma) and kojic acid (Hkoj) and rationalized on the basis of DFT simulations. All the ligands L^– form [VOL]⁺, cis-[VOL₂(H₂O)] and cis-[VOL₂(OH)]^– species in aqueous solutions and a square-pyramidal [VOL₂] complex in the solid state, which transforms into cis-[VOL₂(solvent)] when it is dissolved in water or in a coordinating solvent. The coordinating properties of the ligands studied were compared with those of pyridinone [3-hydroxy-1,2-dimethyl-4(1H)pyridinone (Hdhp), and 1,2-diethyl-3-hydroxy-4(1H)pyridinone (Hdepp)] derivatives and catechol (H₂cat), and were explained by postulating that from pyrones to pyridinones and to catechol the donor set changes progressively from (CO, O^–) to (O^–, O^–). DFT calculations allowed us to determine the relative stability of the four possible structures (square pyramidal, trans- and two cis-octahedral) of the bis-chelated species and the aromaticity of the protonated, neutral and deprotonated form of the ligands through the calculation of the HOMA (harmonic oscillator model of aromaticity) index. The relationship between the electric charge on the oxygen donors, the mean distances and the difference between the lengths of C–O_ket and C–O_phen bonds with (i) the pK_a of the ligands, (ii) the pK of deprotonation of the equatorially coordinated water molecule in cis-[VOL₂(H₂O)], and (iii) the ⁵¹V hyperfine coupling constant (A_z) of [VOL₂], cis-[VOL₂(H₂O)] and cis-[VOL₂(OH)]^– was also found and discussed.

The chelating and spectroscopic properties of pyrone and pyridinone derivatives, tropolone and catechol (which form very effective antidiabetic compounds) towards the VO²⁺ ion are explained in terms of aromaticity of the fully deprotonated form of the ligands, and of total electric charge on the oxygen donors.

Paramagnetic gadolinium(III) complexes are widely used to increase contrast in magnetic resonance (MR) images. Contrast enhancement depends on the concentration of the gadolinium complex and on its relaxivity, an inherent property of the complex. Increased relaxivity results in greater image contrast or the ability to detect the contrast agent at a lower concentration. An increase in the relaxivity enables the imaging of abundant molecular targets. Relaxivity depends on the structure of the complex, kinetics of inner-sphere and second-sphere water exchange, and on the rotational dynamics of the molecule. The latter, and in some cases the former, properties of the complex change when it is bound to its target. All of these properties can be rationally tuned to enhance relaxivity. In this Microreview, we summarize our efforts in understanding and optimizing the relaxivity of contrast agents targeted to serum albumin and to fibrin.

The effect of changing a single donor atom in a gadolinium(III) complex targeting human serum albumin can be seen in the graphic. The single donor group modification alters inner-sphere water exchange by three orders of magnitude and changes relaxivity by a factor of five. Water exchange can be rationally tuned to optimize relaxivity.

Gas-phase addition of a basic ligand to dipositive uranyl coordination complexes comprising diacetone alcohol (DAA) results in water-elimination, which indicates aldol dehydration of DAA to produce mesityl oxide. A novel attribute of the observed gas-phase chemistry is that a ligand exothermically associates to a coordination complex to provide the excitation required to induce chemistry in other ligands, with the added “spectator ligand” remaining intact in the product. Dehydration of DAA was observed for addition of tetrahydrofuran, acetone, and 2-propanol to uranyl complexes [UO₂(DAA)₂]²⁺ and [UO₂(DAA)(acetone)₂]²⁺. In contrast, [UO₂(DAA)₂(acetone)]²⁺ did not exhibit ligand-addition chemistry, which is attributed to a high degree of coordinative saturation at the uranium metal center.

Gas-phase addition of a basic ligand to dipositive uranyl coordination complexes comprising diacetone alcohol results in dehydration to produce mesityl oxide. A novel attribute of this process is that a ligandexothermically associates to a coordination complex, providing excitation to induce chemistry in other ligands; the added “spectator ligand” remains intact.

The second polyhydridoniobocene complex that was characterized by X-ray diffraction is reported. On the basis of H–H distances and H–Nb–H angles, [Nb(η⁵-C₅H₄SiMe₃)₂(H)₃] (1) is classified as a “compressed hydride”. Compound 1 acts as an efficient single-component initiator for the ring-opening polymerization of ϵ-caprolactone and δ-valerolactone. ϵ-Caprolactone and δ-valerolactone are both polymerized within a few hours to yield high-to-medium-molecular-weight polymers with medium to broad polydispersities. Polymer end-group analysis showed that the polymerization proceeds through a coordination–insertion mechanism based on the cleavage of the ring between the oxygen atom and the acyl carbon atom.

The structure of [Nb(η⁵-C₅H₄SiMe₃)₂(H)₃] (1) justifies its classification as a “nonclassical” transition metal hydride. Complex 1 is an initiator for the ROP of lactones. A mechanism consisting of an interaction between the lactone carbonyl group and the metal, insertion of the lactone into the Nb–H bond, and the generation of a metal alkoxide–aldehyde propagating species has been proposed.

Highly multibranched gold nanostars were obtained by a room-temperature synthesis assisted by deep-eutectic solvents (DES). The concentration of the ascorbate ions and the presence of water in the solution were found to both have a profound influence on branch formation. A growth mechanism of the nanostar is therefore proposed from the analysis of the particle dimensions, the aspect ratio of their protuberances, and the gold crystal size. These spiky nanoparticles would find an application as conductive filler in polymeric piezoresistive composites, based on a tunneling conduction mechanism.

The dimension and morphology of gold nanostars, prepared through a room-temperature synthesis assisted by deep-eutectic solvents, can be tuned by varying the concentration of water and L-ascorbic acid. The obtained shapes fit with the requirements for the preparation of piezoresistive composites based on a tunneling conduction mechanism.

[Fe(CO)₂(SCH₂CH₂NH₂)₂] (1, CORM-S1), [Fe(CO)₂(SC₆H₄-2-NH₂)₂] (2, CORM-S2), [Ru(CO)₂(SCH₂CH₂NH₂)₂] (3), and [Ru(CO)₂(SC₆H₄-2-NH₂)₂] (4) were prepared from the corresponding metal carbonyl compounds and cysteamine (deprotonation of the thiol functionality) or cystamine (oxidative addition of the S–S bond). They crystallized from donor solvents, such as tetrahydrofuran and dimethylformamide, as adducts with the bases bound by hydrogen bridges to the amino functionalities. Although the iron derivatives proved to be valuable photosensitive CO-releasing molecules (CORMs), CO was not released from the ruthenium analogs with visible light.

CO-releasing molecules are important as therapeutic agents and pharmaceuticals. Light-triggered CO release can be achieved for iron-containing carbonyl complexes stabilized with aminoethylthiolate or related bases, whereas homologous ruthenium derivatives are stable when exposed to visible light. These complexes capture neutral Lewis bases through N–H···O hydrogen bridges.

Ferrocenylmaleimides have been synthesized from 2,5-dibromo-N-methyl-1H-pyrrole. Bromine shift and oxidation of the pyrrole core with subsequent ferrocenylation using the Negishi C–C cross-coupling protocol led to the formation of 3-ferrocenyl-N-methylmaleimide (3), 3-bromo-4-ferrocenyl-N-methylmaleimide (4), and 3,4-diferrocenyl-N-methylmaleimide (5). The structural properties of 4 and 5 were investigated by single-crystal X-ray diffraction. Cyclic and square-wave voltammetry, in situ UV/Vis/NIR and IR spectroelectrochemistry (5) highlight the electrochemical properties of these compounds. Compounds 3 and 4 exhibit one reversible ferrocenyl-based redox event, whereas 5 shows two separate electrochemically reversible one-electron transfer processes with remarkably high ΔE°′ values and reduction potentials of E₁°′ = 50 and E₂°′ = 380 mV (ΔE°′ = 330 mV), respectively, with [NBu₄][B(C₆F₅)₄] as the supporting electrolyte. The NIR measurements confirm the electronic communication between the iron centers (Fe^II/Fe^III) as intervalence charge transfer absorptions were observed in 5⁺. Compound 5 was classified as a weakly coupled class II system, according to Robin and Day. UV/Vis investigations of the solvatochromic behavior of 3–5 revealed the complex solvation of these push–pull systems, which reflects that three important solvent properties (hydrogen bond formation ability, polarizability, and solvation of the carbonyl group and the C=C bond) affect _max.

Ferrocenylmaleimides are accessible by bromine shift and oxidation with subsequent Negishi ferrocenylation of dibromo-N-methylpyrrole. Electrochemical and spectroelectrochemical studies highlight their redox and electron-transfer properties. Additionally, the ferrocenylmaleimides show a significant solvatochromic behavior.

Treatment of a variety of zwitterionic amino-arenesulfonic acids with silver oxide has resulted in the synthesis of seven new Ag^I amino-arenesulfonates [Ag(O₃SR)]_∞ [R = o-aminobenzyl (oAB) (1), m-aminobenzyl (mAB) (2), 6-amino-3-methoxybenzyl (6A3MB) (3), o-aminonaphthyl (oAN) (4), 5-aminonaphthyl (5AN) (5), 4-amino-3-hydroxynaphthyl (4A3HN) (6) and 5-isoquinolinyl (I) (7)]. This has allowed an exploration of their coordination chemistry, whereby we examine the impact of structural diversity in the anions: the position of the amino functionality on the arene moiety, inclusion of the N within a heterocycle and an increase in ring size from phenyl to naphthyl. The solid-state structures of 1, 2 and two forms of 4, one with a coordinated water molecule, have been determined by X-ray diffraction and are all polymeric. Analytical data is provided for two of the structurally known complexes: known silver p-aminobenzenesulfonate 8 [Ag(O₃SBAp)]_∞ and Ag^I 2-pyridinesulfonate [Ag(O₃SP)]_∞ (9). The composition of all nine complexes has been confirmed through NMR spectroscopy, MS-ES⁺, FTIR and elemental analysis.

Silver(I) amino-arenesulfonate complexes of the formula [Ag(O₃SR)]_∞ were formed through treatment of a variety of amino-arenesulfonic acids with Ag₂O in water. Crystal structure analysis on four complexes indicate 1D chains and 2D and 3D networks depending on the nature and position of the amino (or N) substituent. FTIR and MS studies suggest all the complexes are polymeric in the solid state.

A series of ruthenium carboxylate complexes that contain two different anionic ligands was prepared. The complexes that bear iodide ligands exhibit remarkable chemical stability. Such complexes have a diminished tendency to undergo anionic ligand exchange and can be activated byvarious acids to form catalysts, which are active in olefinmetathesis reactions.

Ruthenium carboxylate complexes that contain an iodide ligand exhibit remarkable stability. Such complexes can be activated by various acids (HA) to form mixed ligand catalysts 12, which are active in metathesis reactions and possess a diminished tendency for anionic ligand exchange.

A series of mono-, di-, tri-, and tetra-triphenylamine (TPA)-substituted porphyrinatozinc complexes have been synthesized to investigate their spectral and electrochemical properties. The varied shapes of absorption spectra of porphyrin–triphenylamine (Por–TPA) conjugates in comparison with tetramesitylporphyrinatozinc (ZnTMP) indicate that there are strong interactions between porphyrin and TPA moieties. In general, the electron-donating capability of a substituent on TPA and the number of TPA derivatives that bond with porphyrin would cause Soret band broadening and intensification of the Q(0,0) band. Due to the antenna effect of these conjugates, the fluorescence quantum yields were enhanced when more TPA moieties were linked. Cyclic voltammetry and spectroelectrochemical methods revealed the redox properties of Por–TPA conjugates. Axial ligation of porphyrinatozinc with N-methylimidazole was useful in differentiating the oxidation site of Por–TPA conjugates. The first one-electron oxidations of these conjugates are at the porphyrin ring. The charge-transfer bands present in the near-IR region in the absorption spectra of Por–TPA radical cations are evidence of an electronic interaction between porphyrin and TPA. The electron-donating strength of the TPA group and the symmetry of the Por–TPA conjugate affect the intensity of the charge-transfer band.

A series of porphyrin–triphenylamine (TPA) conjugates have been characterized by spectral and electrochemical methods. Due to the antenna effect of these conjugates, the fluorescence intensity was enhanced. The oscillator strength increases as the number of TPA substituents increases for the charge-transfer band in the near-IR region upon porphyrin-ring oxidation.

Proteins sharing the same “2-His-1-carboxylate” structural motif have little amino acid sequence similarity and are able to perform many different reactions. Many factors have been cited to explain their different specificity and turnover rates, like protein environment, coordinated ligand geometry, electronic structure of the active site, etc. In this paper, we present a combined approach applying high-resolution XANES spectroscopy and theory simulations to different model complexes that mimic the binding modes of the amino acids to the metal site. Experiments were performed on three compounds showing three metal sites: ferrous hexacoordinate, ferric pentacoordinate and ferrous pentacoordinate. The first two compounds bear an N,N,O-tridentate 3,3-bis(1-alkylimidazol-2-yl)propionate ligand that features a monodentate carboxylate group. These complexes mimic the activity of extradiol dioxygenases but also exhibit intradiol cleavage activity. The third compound features a bidentate terphenylcarboxylate ligand and a sterically hindered bidentate N,N-donor, thus providing a good structural mimic of the ternary enzyme-tetrahydrobiopterin-substrate complex in pterin-dependent phenylalanine hydroxylase, which also contains a bidentate carboxylate. Modeling of high-resolution XANES on well-defined model complexes of different geometry can aid in protein structure elucidation. XANES gives the oxidation state and coordination number of the metal in the non-crystallized protein at natural pH. The accuracy of the results is limited by the core-hole and experimental broadenings. We found that high-resolution XANES experiments give increased resolution at the pre-edges, but limited improvement at the main edge. These high-resolution pre-edges can be accurately simulated by using crystal field multiplet theory (CFM). We show that by combining modelling and XANES simulations with FEFF8, detailed structural and chemical information can be obtained. We found that a short O2–metal distance for the carboxylate oxygen atom not bound to the metal causes a higher white line in Fe^II, which is similar to the results obtained for the pterin-dependent hydroxylase, tyrosine hydroxylase (TYH). Full-potential FDMNES simulations for each sample confirm the accuracy of the main results with muffin-tin approximation (FEFF8).

A combined spectroscopic and theoretical method to study the binding mode of amino acids to a metal is discussed. Three compounds showing three metal sites: ferrous hexacoordinate, ferric pentacoordinate and ferrous pentacoordinate were studied. The work shows the subtle correlation between structure and the absorption edge features.

The combination of AgNO₃ and trans-[Pt(ma)₂(Hpz)₂]²⁺ (1; ma = methylamine; Hpz = neutral pyrazole) in water yields mixed Pt,Ag coordination polymers of different stoichiometries, depending on the ratio between Ag and Pt, as well as the pH. The products that were isolated and X-ray structurally characterized display both conventional (Ag⁺ coordination to pyrazole-N) and unconventional Ag⁺ binding modes (η¹ and η² binding to C atoms of the pyrazole/pyrazolate ligands; Pt → Ag dative bonds). Specifically, in trans-[Pt(ma)₂(Hpz)₂]Ag₂(NO₃)₄ (2) and in trans-[Pt(ma)₂(pz)₂]₂Ag₃(NO₃)₃ (4), silver ions bind to C4 positions of Hpz (2) and pz^– (4) ligands in η¹ fashions, with Ag–C distances of 2.574(4) and 2.643(16) Å, respectively. In 4 there is additional cross-linking by a second Ag⁺ of N2 sites of adjacent pz^– rings, further reinforced by weak dative bonds from Pt to Ag. Ag–N coordination to both a neutral Hpz and an anionic pz^– ligand is observed in trans-[Pt(ma)₂(pz)₂]Ag₂(Hpz)₂(NO₃)₂ (5), with individual trinuclear PtAg₂ entities associated through weak η² contacts that involve the C3 and C4 positions of the neutral Hpz ligands. As in 4, intramolecular Pt–Ag distances of 3.1374(6) Å suggest weak dative bond interactions between Pt and Ag. The acidities of the two Hpz ligands in 1 are distinctly different (pK_a values of 7.25 and 9.08 in H₂O), thereby suggesting a stabilization of the monodeprotonated species trans-[Pt(ma)(Hpz)(pz)]⁺ (1c) in solution, probably through intermolecular hydrogen-bond formation between Hpz and pz^– ligands.

Not (only) the available second-ring N atom of pyrazole and pyrazolate ligands in complexes of Pt^II appears to be the preferred Ag⁺ binding site in moderately acidic aqueous solution, but rather the C4 atom and/or the C4,C5 double bond.

New polyfunctional bidentate and tetradentate trifluoromethylated enaminone ligands that bear redox-active and photosensitive moieties were synthesized in moderate to good yields and their coordination chemistry with copper(II) was examined. The crystal structures revealed the formation of mononuclear Cu^II complexes with all ligands, where the metal ion is located in almost perfect to distorted square planar environments. The deviation from an ideal square plane influences the redox potentials of the metal centre within the complex as demonstrated by cyclic voltammetry. For all the complexes, a stable Cu^I species was evidenced by a quasireversible reduction step at potentials from –0.48 to –1.08 V (potential standards E⁰), but the most stable Cu^I species originated from the Cu^II complex with the tetradentate ligand. UV/Vis absorption spectra revealed no major differences between the ligands and their Cu^II complexes.

Structural variation of the trifluoromethylated enaminone building block gave rise to new bidentate and tetradentate ligands that bear redox-active units (anthracene, azobenzene and tetrathiafulvalene). Their coordination chemistry with copper(II), structural characterization, redox chemistry and UV/Vis properties of the ligands and complexes have been investigated.

Hydroxyapatite (HAP) microspheres composed of nanorods have successfully been prepared by a facile co-precipitation method without any template. We propose the formation mechanism of the microspheres to be a four-step process on the basis of the evolution of their morphology as a function of reaction time. We investigate the competitive sorption of the HAP microspheres for Pb²⁺, Cu²⁺, Cd²⁺, Zn²⁺, and Ni²⁺ to show that HAP microspheres are a highly selective adsorbent for Pb²⁺ in wastewater.

Hierarchically structured microspheres self-assembled from hydroxyapatite nanorods have successfully been prepared by a simple co-precipitation method without any template. The as-prepared materials exhibit high selective adsorption for Pb²⁺ in wastewater.

The tBu₂Sn-bridged [1]troticenophane [(η⁷-C₇H₆)Ti(η⁵-C₅H₄)]SntBu₂ (2) has been synthesized by low-temperature salt elimination reaction between stoichiometric amounts of the dilithiated troticene [(η⁷-C₇H₆Li)Ti(η⁵-C₅H₄Li)]·pmdta (1; pmdta = N,N′,N′,N″,N″-pentamethyltriethylenetriamine) and tBu₂SnCl₂. Compound 2 was isolated as a blue-green crystalline solid in moderate yield and characterized by multinuclear ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy, UV/Vis spectroscopy and elemental analysis. Compound 2 and the co-crystal 2·[(pmdta)LiCl] were characterized in the solid state by X-ray diffraction analyses. The dihedral angles between the planes of the C₅H₄ and C₇H₆ rings are 16.3(3) and 17.2(1)°, respectively, for 2 and its co-crystal. Compound 2 is the first monocrystalline structurally characterized heteroleptic stanna[1]troticenophane. The reaction of 2 with [Pt(PEt₃)₃] afforded the platinastanna[2]troticenophane 3, in which the Pt⁰ fragment was inserted by regioselective cleavage of the ipso-C₇H₆–Sn bond, as evidenced by ¹³C NMR spectroscopy and X-ray diffraction analysis. Compound 2 underwent thermal ring-opening polymerization in the solid state to form poly(troticenylstannane) 4. In solution and in the presence of nBuLi as initiator, 2 opens and reassembles to form the metallopolymer 5. The polymeric nature of both 4 and 5 was determined by gel permeation chromatography.

The synthesis of a tBu₂Sn-bridged ansa-cycloheptatrienyl-cyclopentadienyl titanium sandwich complex is presented. As a result of its tilted structure, this strained stanna[1]troticenophane is easily converted into poly(troticenylstannanes) by ring-opening polymerization and undergoes regioselective insertion of platinum(0) into the ipso-C₇H₆–Sn bond upon reaction with [Pt(PEt₃)₃].

Conflicting results have been reported with respect to the photoinduced switching of the magnetic properties of [Fe^III(salten)]⁺ complexes [salten = 4-azaheptamethylene-1,7-bis(salicylideneiminate)] coordinated by photoisomerizable ligands. In order to address this problem, two Fe^III complexes [Fe(salten)(3-azpy)]BPh₄ (1) and [Fe(salten)(4-azpy)]BPh₄ (2) have been synthesized and characterized by various physicochemical methods (azpy = phenylazopyridine). Both 1 and 2 exhibit a low spin (S = 1/2) to high spin (HS, S = 5/2) transition in the solid state. In solution at room temperature both complexes are predominantly HS. Upon exposure to 310 (trans → cis) and 440 nm radiation (cis → trans) the free and coordinated 3- and 4-azpy ligands undergo a reversible cis–trans isomerization. For 2 a corresponding reduction of the HS fraction 2 % is observed, whereas in 1 no effect is observed. Extensive DFT calculations, which employ different functionals and basis sets, explain this experimental result. The consequences of these findings with respect to the design of spin-switchable iron(III) complexes with photoactive ligands are discussed.

[Fe(salten)(3-azpy)]BPh₄ (1) and [Fe(salten)(4-azpy)]BPh₄ (2) have been synthesized and characterized [salten = 4-azaheptamethylene-1,7-bis(salicylideneiminate), azpy = phenylazopyridine]. Both exhibit a low to high spin transition in the solid state and are predominantly high spin in solution. cis–trans isomerization of coordinated azpy leaves their spin equilibria almost unaffected.

Six new tetranuclear copper(II) complexes were prepared exploiting novel ditopic alkylenediamine-N,N,N′,N′-tetraphenolate ligands. The geometrical parameters of the compounds can be varied by introducing different solvents of crystallization into the lattice. The structures of all six complexes were determined from single-crystal X-ray diffraction analyses and the magnetic properties of the complexes were estimated by computational DFT calculations. The relationship between the magnetic exchange coupling constant (J) and the Cu–O–Cu angle (θ) in these bis(phenoxido)-bridged complexes was investigated and a magnetostructural correlation was established between J and the θ angle. All studied complexes showed strong antiferromagnetic behaviour.

The geometrical parameters and magnetic properties of structurally interesting metal–organic macrocycles {[Cu₄(L)₂]·xS and [Cu₄(L)₂(H₂O)₂]·xS} can be varied drastically by changing the crystallization solvent. Six novel structures are reported along with their calculated magnetic coupling constants.

A comparative study of the coordination modes of a (thiophosphinoyl)(trimethylsilyl)methanide (1^–·Li⁺) and bis(thiophosphinoyl)methanide (2^–·Li⁺) ligand with Rh^I was carried out. Several complexes were synthesized and characterized. For 1^–·Li⁺, C~S coordination is forced, whereas for 2^–·Li⁺, S~S and C~S coordination can be achieved. In one case, a dynamic equilibrium between these two modes of coordination was observed. DFT calculations were carried out to rationalize this phenomenon and the stability of the methanide compounds.

The reactions of mono and bis(thiophosphinoyl)methanides with an Rh^I precursor yielded tetracoordinate Rh^I complexes in which different coordination modes of the ligands have been observed.

α- and γ-Fe₂O₃ nanorods have been prepared from a β-FeOOH precursor that was obtained by aqueous-phase precipitation of ferric chloride. The oxyhydroxide precursor had a rodlike shape with a diameter of 30–40 nm and a length of 400–500 nm. Calcination at 500 °C of the rod-shaped oxyhydroxide in air yielded α-Fe₂O₃ nanorods, whereas heating to reflux in polyethylene glycol (PEG) at 200 °C resulted in the formation of γ-Fe₂O₃ nanorods. Both oxides inherited the rodlike morphology of the precursor but exposed different crystalline facets. When being used to catalyze NO reduction by CO, an environmentally important reaction in NO abatement, the γ-Fe₂O₃ nanorods were much more active than the α-Fe₂O₃ nanorods and showed an apparent crystal-phase effect. This was because the γ-Fe₂O₃ nanorods simultaneously exposed iron and oxygen ions on their surfaces, which facilitated the adsorption and activation of NO and CO molecules.

α- and γ-Fe₂O₃ nanorods were obtained by proper dehydration of a rod-shaped β-FeOOH precursor. The Fe₂O₃ nanorods showed a distinct crystal-phase effect in the reduction of NO by CO on the basis of their exposed surface facets.

A new end–core–end naphthalenediimide-based ligand N,N′-bis(3-imidazol-1-yl-propyl)naphthalene diimide (3-imntd) was synthesized. Single crystals of the free ligand and its Hg^II, Cd^II, and Cu^II halide complexes were obtained. All the compounds were fully characterized by elemental analysis, IR spectroscopy, single-crystal XRD, and DFT studies. The XRD and DFT calculations revealed three different kinds of conformations for 3-imntd (cis, trans, and L). The variation in the ligand conformation and the resulting final structures of the coordination assemblies, M₂L₂ metallacycle, 1D zigzag chain, or ML metallacycle, seem to be induced by the different geometric characters of the coordination tetrahedra around the metal centers. The optical and electrochemical properties of the compounds were also investigated.

Self-assembly of an end–core–end naphthalenediimide-based ligand with Hg^II, Cd^II, and Cu^II halides leads to the formation of an M₂L₂ metallacycle, 1D zigzag chain, or ML metallacycle, which are directed by the geometric preference of the halide anions, metal centers, and conformational adaptation of the ligand.

When treated with Et₂Zn, the tetradentate Schiff base N,N′-ethylenebis(4-iminopentan-2-one) (H₂L) led to the formation of dimers, [L₂Zn₂], a tetranuclear complex, [L₄Zn₄] (1) and a polymeric material [LZn(Et)]_n (2), thus highlighting the coordinative versatility of the ligand. Halogenation of 1 with SO₂Cl₂ or Br₂ afforded in moderate yield the dinuclear zinc complexes [LZn(thf)·ZnCl₂] (3) and [LZn(thf)·ZnBr₂] (4). [LZn·ZnI(μ-OEt)]₂ (5) was isolated from the reaction of an in situ generated mixture of 1 and 2 with iodine. This product likely results from adventitious oxygen in the reaction mixture. This was seemingly confirmed by the diffusion of air into a solution of 2 in toluene, thereby resulting in a pentanuclear zinc complex, [(LZn·ZnEt)₂{Zn(μ-OEt)₄}] (6). Complex 6 features a central Zn(OEt)₄ unit, in which the ethoxide groups bridge two dinuclear fragments. The identities of complexes 1–6 were conclusively identified by X-ray crystallography, thereby revealing similar structural features that were confirmed by spectroscopic data and, for 1–5, supported by DFT calculations.

The coordination preferences of the tetradentate Schiff base N,N′-ethylenebis(4-iminopentan-2-one), H₂L, with Et₂Zn under various stoichiometries were investigated and the reactivity of the resultant products was explored. These reactions afforded a series of di-, tetra- and polynuclear zinc complexes.

Heterobimetallic lithium–iron coordination compounds are interesting targets for several reasons: they can be used as precursors for mixed metal oxides, as catalysts, for example, for ring-opening polymerization reactions or to study oxidation/reduction processes. Finally their magnetic properties are also of interest. New heterobimetallic aryloxide complexes, namely [(thf)₄Li₃Fe(OPh)₃(O₂C₆H₄)Cl]₂ (1), [{(thf)₃Li₃Fe(OPh)₅Cl}₃]_n (2), and[(thf)₃Li₃Fe(OPh)₆]₂ (3), have been synthesized and characterized by single-crystal X-ray diffraction. While compounds 1 and 3 were synthesized by an oxidative substitution reaction, compound 2 was directly obtained from the Fe^III salt. These compounds are accessible by both synthetic pathways. Additionally, in compound 1, the phenoxy ligand was catalytically oxidized to ortho-catechol, which was incorporated into the structure of 1 as a ligand that coordinates strongly to iron. All compounds feature the Fe^III ion with a trigonal, bipyramidal environment, with coordination number 5.

Three new pentacoordinate Fe^III complexes, [(thf)₄Li₃Fe(OPh)₃(O₂C₆H₄)Cl]₂ (1), [{(thf)₃Li₃Fe(OPh)₅Cl}₃]_n (2), and [(thf)₃Li₃Fe(OPh)₆]₂ (3), two dinuclear, molecular species (1 and 3) and one trinuclear 1D coordination polymer, are reported. Compound 1 has a coordination sphere close to a square pyramid and might thus be useful for applications such as catalyst for the ring-opening polymerization of lactide.

Molecular imaging relies on the availability of imaging probes designed to modify their efficiency in the presence of a specific parameter, among which pH is one of the most investigated. Introduction of an aminoethyl moiety into the well-known DO3A platform imparts the desired pH sensitivity to the corresponding Gd³⁺ complex. The amine group is accessible and easy to functionalize; in particular, the possibility of tuning its pK_AH through N-substitution makes it a good pH-responsive functionality to access a novel class of tailored pH-sensitive MRI contrast agents. This was demonstrated by a relaxometric study on a functionalized Gd-DO3A complex bearing a simple primary amine group and comparison with the results of the corresponding N,N-dimethyl analogue.

Gd³⁺ complexes of aminoethyl-substituted DO3A show pH-sensitive behaviour with a relaxivity jump close to physiologically relevant pH values. The response to pH of this novel platform may be fine tuned by N-substitution.

Bimodal magnetic resonance imaging (MRI)/optical probes for bioimaging were obtained by grafting two types of lanthanide metal ions, Gd³⁺ and Eu³⁺/Tb³⁺, on the surface of SiO₂ nanoparticles. The resulting systems were endowed with relaxometry and photoluminescent properties, respectively. Grafting a pyridine-based aromatic backbone on to the silica surface enhances the emission quantum yield of the Eu³⁺-containing nanoparticles fivefold compared to similar systems that bear no aromatic antennae. The emission properties of the mixed Ln³⁺/Gd³⁺-based nanoparticles are not influenced by the presence of Gd³⁺. The relaxometric properties of these samples are slightly better than the properties of commercial [Gd(DTPA)]₂ (DTPA = diethylenetriaminepentaacetate). When taken up by RAW 264.7 cells (mouse macrophage cell line), such bimodal probes exhibit both T₁-weighted MRI increased contrast and fluorescence tracking.

Grafting two lanthanides, Gd³⁺and Eu³⁺/Tb³⁺, to a single SiO₂ nanoparticle provides a bimodal bioimaging probe with luminescent and magnetic functionalities. The use of a pyridine bridge enhances the Ln³⁺ emission properties. After internalization in mouse macrophage cells, the bimodal probes exhibit both T₁-weighted MRI increased contrast and efficient optical tracking by fluorescence.

A straightforward synthesis method for mixed phosphane dipyrido-annelated N-heterocyclic carbene (dipiy) palladium(II) complexes is presented. The key step is the oxidative addition of 6-bromodipyridoimidazolium bromides that can be prepared easily from dipyridine in a two step reaction. This new procedure avoids any generation of the free carbene as well as any transmetallation step.

The straightforward synthesis of mixed dipyrido NHC-phosphane Pd^II complexes by the oxidative addition of 6-bromodipyridoimidazolium salts is presented. This procedure avoids any transmetallation step orformation of a free carbene. Synthesis of the brominated starting material can easily be achieved by reaction of the corresponding imidazolium or benzoylimidazolium salt with bromine.

DFT led to the discovery of two new structural motifs in tetranuclear iron carbonyl thiocarbonyls, Fe₄(CS)₄(CO)_n (n = 12, 11, 10, 9), which are not found in their homoleptic analogues, Fe₄(CO)_n+4. Thus the lowest energy Fe₄(CS)₄(CO)₁₂ structures have a central Fe₃ triangle with an exotriangular iron atom joined to the Fe₃ triangle through a four-electron donor CS bridge. This contrasts with the structure of Os₄(CO)₁₆ and the predicted structure of Fe₄(CO)₁₆, which consist of an M₄ rhombus and two-electron donor carbonyl groups. An even more remarkable new structural motif for the Fe₄(CS)₄(CO)_n derivatives is the irregular Fe₄ “rhombus” (actually a trapezium) bridged by a six-electron donor η²-μ₄-CS group. This type of structure is found in the lowest energy structures of both Fe₄(CS)₄(CO)₁₀ and Fe₄(CS)₄(CO)₉ and makes Fe₄(CS)₄(CO)₁₀ viable enough to be a promising synthetic objective. On the contrary, Fe₄(CS)₄(CO)₁₁ is found to be thermochemically unfavorable both with respect to CO dissociation and disproportionation into Fe₄(CS)₄(CO)₁₂ and Fe₄(CS)₄(CO)₁₀.

The lowest energy Fe₄(CS)₄(CO)₁₂ structures have a central Fe₃ triangle with an exotriangular iron atom joined to the Fe₃ triangle by a four-electron donor “end-on” CS bridge. An Fe₄ rhombus bridged by a six-electron donor η²-μ₄-CS group is found in the lowest energy structures of Fe₄(CS)₄(CO)₁₀ and Fe₄(CS)₄(CO)₉ and makes Fe₄(CS)₄(CO)₁₀ viable enough to be a promising synthetic objective.

Diorganotin(IV) derivatives of 4-acyl-5-pyrazolones Q₂SnR₂ [HQ = 3-methyl-1-phenyl-4-R-5-pyrazolone: HQ^nPe, R = neopentylcarbonyl; HQ^iPr, R = isopropylcarbonyl; HQ^tBu, R = tert-butylcarbonyl; HQ^Cy, R = cyclohexylcarbonyl; HQ^Cp, R = cyclopentylcarbonyl; HQ^EtCp, R = (ethylcyclopentyl)carbonyl] have been synthesized and characterized spectroscopically (IR, far-IR, ¹H, ¹³C and ¹¹⁹Sn NMR) and structurally (X-ray). Steric bulkiness in the acyl fragment of HQ^tBu induces partial dissociation in solution of (Q^tBu)₂SnMe₂, which exists as an equilibrium mixture of six- and five-coordinate tin species. Single-crystal X-ray structure determinations of several representative complexes are presented. Whereas the dialkyltin(IV) complexes are always trans-octahedral, a diphenyltin(IV) derivative exists in the solid state that has the two phenyl groups in a cis arrangement. DMol3 and CASTEP DFT studies of this unprecedented cis, and the corresponding trans configurations, show the former to be slightly more stable, in agreement with the diffraction study. Solid-state ¹¹⁹Sn cross-polarization magic-angle spinning NMR spectroscopic data show that the isotropic chemical shifts (δ_iso,mas) and chemical-shift anisotropies/spans (Δδ/Ω) that characterize the diphenyl(IV) derivatives are markedly removed from values measured for the corresponding dimethyl and di-n-butyl derivatives, thereby adding further evidence for a stable cis configuration in the diphenyl(IV) systems. This is supported by GIPAW DFT calculation of the ¹¹⁹Sn isotropic shifts and chemical-shift anisotropies/spans from fully relaxed structures by using the CASTEP code, which provides a direct link between the cis diphenyl(IV) arrangement and the reported differences in the ¹¹⁹Sn NMR spectroscopic parameters.

Diorganobis(4-acyl-5-pyrazolonato)tin(IV) complexes have been synthesized and characterized spectroscopically (IR, far-IR, ¹H, ¹³C and ¹¹⁹Sn NMR) and structurally (X-ray) to gain further insight into the cis versus trans configuration in octahedral metal diketonates.

Magnetic resonance imaging (MRI) is a powerful imaging modality for visualizing anatomical soft tissue using nonionizing radiation. Compared with other molecular imaging methods such as optical, nuclear, and ultrasound, sensitivity is limited but can be improved through development of chemical agents which enhance MRI contrast. MRI Contrast agents that function through paramagnetic chemical exchange saturation transfer (paraCEST) are currently being investigated as an alternative to T₁ and T₂ contrast agents. These agents may be designed as imaging probes which are intrinsically responsive to pH and temperature. Trivalentlanthanide complexes have dominated the relatively young field of paraCEST for just over a decade. Recently, high spin Fe^II complexes containing labile amide and amino protons which chemically exchange with bulk water have emerged as viable additions to the repertoire of paraCEST agents. This microreview will provide an overview of some considerations when designing paraCEST contrast agents which incorporate high spin Fe^II as the paramagnetic metal center. Important factors such as paramagnetic relaxation and hyperfine shifts, spin state, coordination, oxidation state, and stability will be discussed in regard to transition metal ion paraCEST contrast agent design.

Paramagnetic metal ions are important for the development of MRI contrast agents that function through chemical exchange saturation transfer (CEST or paraCEST). Recent work shows that Fe^II paraCEST MRI contrast agents are promising new candidates to add to the current repertoire of lanthanide(III) complex contrast agents.

Two new tripodal heptadentate ligands, H₄dpaba (N,N′-bis[(6-carboxypyridin-2-yl)methyl]aspartic acid) and H₃mpatcn(1,4-bis(methoxycarbonyl)-7-[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane), which bear one or two picolinate pendant arms, have been synthesised. Their lanthanide complexes have been characterised by NMR and fluorescence spectroscopy and potentiometry. Both ligands gave rise to water soluble 1:1 complexes with an increased thermodynamic stability (pGd_dpaba = 13.3, pGd_mpatcn = 11.8, with pGd_L = –log [Gd]_free at pH 7.4, [Gd]_total = 1 μM and [L]_total = 10 μM) with respect to the analogous bisaqua complex [Gd(tpaa)(H₂O)₂] [H₃tpaa = α,α′,α″-nitrilotri(6-methyl-2-pyridinecarboxylic acid), pGd_tpaa = 11.2). The two inner-sphere water molecules confer sizeable relaxivities (r₁) to the complexes at high field at physiological pH: r₁ = 8.90 and r₁ = 7.35 mM^–1 s^–1 have been measured in HOD at 200 MHz for [Gd(dpaba)(HOD)₂]^– and [Gd(mpatcn)(HOD)₂], respectively. Their relaxometric properties have been investigated by NMRD (Nuclear Magnetic Relaxation Dispersion) and ¹⁷O NMR spectroscopy. The formation of ternary complexes with physiological anions, such as acetate, hydrogen carbonate, hydrogen phosphate and citrate, has been monitored by ¹H NMR spectroscopy at 200 MHz and pH 7.4. The addition of a large excess (0.6 M) of acetate, hydrogen phosphate and citrate led to the formation monoaqua ternary complexes. Even under these conditions, the average relaxivity remains higher or similar than most currently used contrast agents. Only hydrogen carbonate interacts strongly with the complexes and coordinates in a bidentate mode by displacing both water molecules to induce a twofold decrease in the relaxivity. Both complexes interact with serum albumin to form a macromolecular adduct with increased relaxivity. In particular, a twofold increase of relaxivity has been measured for [Gd(dpaba)(H₂O)₂]^– in bovine serum, which suggests that anion binding does not significantly affect the relaxivity under these conditions.

Two tripodal ligands and their bisaqua Gd^III complexes have been synthesised and characterised by NMR and fluorescence spectroscopy and potentiometry. Both complexes show sizeable relaxivities at highfield. The formation of ternary complexes with oxyanions and bovine serum albumin has been studied, and a twofold increasein relaxivity has been measured for[Gd(dpaba)(H₂O)₂]^– in bovine serum.

New hybrid compounds have been synthesized by functionalization of cobalt and copper layered hydroxides by salen complexes. Two kinds of compounds have been obtained from [M(SalenSO₃Na₂)] (M = Cu²⁺, Ni²⁺, Co²⁺ and Zn²⁺) and the preintercalated copper and cobalt hydroxides Cu₂(OH)₃(DS) and Co₂(OH)₃(DS₀) [SalenSO₃Na₂ = N,N′-bis(5-sulfonatosalicylidene)-1,2-diaminoethane disodium salt, DS^– = dodecylsulfate, DS₀^– = dodecylsulfonate]. The reaction of [M(SalenSO₃Na₂)] with layered copper hydroxide led to the anion-exchanged compounds Cu₂(OH)_3.00(CuSalenSO₃)_0.50·0.20H₂O [Cu(SalenSO₃)Cu (1)] and Cu₂(OH)_3.24(NiSalenSO₃)_0.38·2.6H₂O [Ni(SalenSO₃)Cu (2)] where M = Cu²⁺ or Ni²⁺. Similarly, the reaction with layered cobalt hydroxide leads to the exchanged compounds Co₂(OH)_3.18(NiSalenSO₃)_0.41·4.0H₂O [Ni(SalenSO₃)Co (6)] and Co₂(OH)_3.44(CoSalenSO₃)_0.28·3.7H₂O [Co(SalenSO₃)Co (8)] where M = Ni²⁺ or Co²⁺. The reaction of [M(SalenSO₃)Na₂] with layered copper hydroxide where M = Co²⁺ or Zn²⁺ and that of layered cobalt hydroxide where M = Cu²⁺ or Zn²⁺ resulted in the modification of the host structure because of concomitant partial cation exchange between the salen complex and the inorganic layers. Mixed-ion-exchanged compounds were obtained, Cu_1.16Co_0.84(OH)_3.28(CoSalenSO₃)_0.36·6.4H₂O [Co(SalenSO₃)Cu/Co (4)], Cu_0.7Zn_1.30(OH)_3.20(ZnSalenSO₃)_0.40·2.11H₂O [Zn(SalenSO₃)Cu/Zn (3)], Co_1.72Cu_0.28(OH)_3.28(CuSalenSO₃)_0.36·3.20H₂O [Cu(SalenSO₃)Co/Cu (5)] and Co_0.80Zn_1.20(OH)_3.20(ZnSalenSO)_0.40·2.25H₂O [Zn(SalenSO₃)Co/Zn (7)]. The magnetic behaviour of the compounds is drastically modified depending on the structure of the inorganic layers induced by the functionalization and partial cation exchange. The hybrid copper layered hydroxides show antiferromagnetic (for 3) or weak ferromagnetic (for 1, 2 and 4) behaviour. The cobalt analogues 5, 6 and 8 are ferrimagnets with ordering temperatures at ca. 6 K, whereas the Co/Zn heterometallic layered simple hydroxide 7 presents dominant antiferromagnetic interactions.

Insertion–grafting of salen-type complexes into copper and cobalt layered hydroxides leads to a drastic modification of the structure and composition of the inorganic layers. The magnetic properties of the heterometallic hybrid layered hydroxides obtained depend strongly on the modification of the inorganic layers induced by the insertion–grafting reaction.

The synthesis, structural, photophysical, theoretical, and electrochemical characterization of four tris(2-phenylpyridine)-based Ir^III complexes are reported. The complexes were functionalized on the pyridine or on the phenyl rings with amide moieties substituted with a tris(ethyl)amine or ethyl groups, thereby yielding a family of compounds with hemicaged or open (without a capping unit but with similar functional groups on the ligand) structure. Within the context of the parent tris(2-phenylpyridine) and the full-cage iridium(III) complexes, structure–photoluminescence quenching relationships (SPQR) of the four complexes have been investigated. Luminescence quenching by oxygen has been studied with Stern–Volmer plots and through evaluation of the thermodynamic parameters involved in the quenching process. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been performed on the complexes to gain insights into structural and electronicfeatures and the nature of the excited states involved in the electronic absorption processes. Interestingly, shielding by the capping unit of moieties in which the LUMO orbital is mostly localized (on the pyridines) results in a dramatic 40 % decrease in oxygen quenching. Conversely, shielding ofmoieties in which the HOMO orbital is partially localized (on the phenyl rings) does not induce any change in the oxygen quenching degree. In both sets of compounds, the thermodynamic feasibility of oxygen quenching is the same for the hemicaged and open compounds, thus giving evidence of the structural origin of such quenching decrease. The SPQR opens up new routes to the design of tailored, more or less sensitive to oxygen, luminescent iridium complexes (e.g., for use as biolabels).

A family of four tris(2-phenylpyridine)-based Ir^III complexes with hemicaged or open (without capping unit but with similar functional groups on the ligand) structure are reported. Within the context of the parent tris(2-phenylpyridine) and the full-cage iridium(III) complexes, structure–photoluminescence quenching relationships (SPQR) of the four complexes have been investigated.

The use of α-benzoin oxime (bzoxH₂) in copper(II) benzoate chemistry, in the absence or presence of ancillary azido ligands, is reported. The reaction of Cu(O₂CPh)₂·2H₂O with one equivalent of bzoxH₂ in N,N-dimethylformamide (DMF) affords the decanuclear complex [Cu₁₀(bzox)₁₀(DMF)₄] (1) in good yield. Dissolution of 1 in CH₂Cl₂ leads to the subsequent isolation of the solvent-free complex [Cu₁₀(bzox)₁₀] (2) in moderate yields. Complexes 1 and 2 are isostructural and possess a loop or single-strand molecular wheel topology. The bzox^2– dianions behave as η¹:η¹:η²:μ₃ ligands, which give rise to an overall [Cu₁₀(μ-ONR)₁₀(μ-OR′)₁₀] core. Both 1 and 2 stack to form nanotubular columns with beautiful supramolecular architectures. The reaction of Cu(O₂CPh)₂·2H₂O with bzoxH₂ and NaN₃ in a 1:1:1 molar ratio in MeOH gives the bzoxH₂-free complex [Cu(N₃)(O₂CPh)(MeOH)]_n (3), which is a 1D chain. The Cu^II atoms in 3 are linked by a single, end-on N₃^– group, a syn,syn-η¹:η¹:μ PhCO₂^– ion, and an oxygen atom from the bridging MeOH ligand. The 1D chains are hydrogen bonded into 2D sheets through N_azide···H(O_MeOH) interactions. Variable-temperature, solid-state direct-current magnetic studies were carried out on 1–3. The data for 1 and 2 indicate very strong antiferromagnetic exchange interactions and a S = 0 ground state, which is expected for even-membered loop arrays of Cu^II atoms. In contrast, 3 exhibits ferromagnetic exchange interactions; the data were fitted to the appropriate equation derived from the Hamiltonian H = –JΣ(S_i·S_i+1), which includes a zJ′ interchain interaction term. The best-fit parameters were J = +49.6(4) cm^–1, g = 2.067(3), and zJ′ = 2.3(1) K. The combined results demonstrate the ligating flexibility of both the bzoxH₂ and azido groups and their usefulness in the synthesis of polynuclear Cu^II clusters and coordination polymers.

The reaction illustrated gives the decanuclear complexes [Cu₁₀(bzox)₁₀(DMF)₄] and [Cu₁₀(bzox)₁₀] (bzoxH₂ = α-benzoin oxime, DMF = N,N-dimethylformamide), which have a single-strand wheel topology, andthe 1D chain [Cu(N₃)(O₂CPh)(MeOH)]_n. The Cu₁₀ clusters are both antiferromagnetically coupled with S = 0 ground states, whereas the 1D chain consists of ferromagnetically coupled S = 1/2 Cu^II ions.

A new family of terpyridine (terpy)-based spin-crossover cobalt(II) complexes, [Co(HO–Cn-terpy)₂](BF₄)₂ [n = 6 (1), 8 (2), 10 (3), 12 (4), and 14 (5)] that possesses a hydroxy-appended long alkyl chain present on the terpyridine skeleton was synthesized and characterized by X-ray structure analysis and temperature-dependent magnetic susceptibility. In the solid state, the compounds 1·H₂O, 4, and 5·H₂O were crystallized in the triclinic P space groups, and their central cobalt(II) ion was coordinated by six nitrogen atoms from two terpyridine units to form a pseudo-octahedral symmetry. In the case of 1·H₂O, one of the terminal hydroxy substituents was involved in hydrogen bonding with a water molecule. For compound 4, on the other hand, both of terminal hydroxy units form a short intermolecular contact with the BF₄^– anion. The temperature-dependent magnetic behavior of 1 and 2 showed a gradual spin crossover, whereas 3 and 4 revealed an abrupt spin transition with a wide thermal hysteresis loop (ΔT = 21 K, T_1/2↑ = 316 K, and T_1/2↓ = 295 K for 3; ΔT = 40 K, T_1/2↑ = 348 K, and T_1/2↓ = 308 K for 4), and 5 exhibits “reverse spin transition” (ΔT = 17 K, T_1/2↑ = 214 K, andT_1/2↓ = 231 K). It has been suggested that compounds 3 and 4 form stronger intermolecular interactions through the fastener effect and hydrogen bonding than 1 and 2. On the basis of a comparison of the resulting magnetic behaviors of the compounds that contain long alkyl chains with a hydroxy group at the end, it was found that the long alkyl chains with the terminal hydroxy group could induce stronger intermolecular interactions between molecules. However, there are many short contacts through the counteranions for 5·H₂O, but thermal motion of the long alkyl chains can be expected. Compound 5 exhibits “reverse spin transition” induced by a structural phase transition.

Cobalt(II) complexes with hydroxy-appended long alkyl chains at the end were synthesized. They were studied by single-crystal X-ray analysis and SQUIDmeasurement. For differences in magnetic behavior, we considered two factors: (i) a fastener effect and (ii) hydrogen bonding by the OH group.

A series of silver and gold complexes bearing N-heterocyclic carbene ligands with a –CH₂CO₂Et pendant group attached to one N atom of the NHC ligand have been prepared. The catalytic properties of the gold complexes toward the decomposition of ethyl diazoacetate (N₂CHCO₂Et) and the transfer of the carbene CHCO₂Et group to benzene and hexane have been investigated. A somewhat different reaction outcome has been found for this family of gold catalysts compared with the parent IPrAuCl catalyst.

Gold-based catalysts containing NHC ligands with potentially coordinating pendant groups have been tested in the functionalization of C–H and C–H bonds by carbene insertion from ethyl diazoacetate, showing moderate catalytic activity.

Microwave chemistry is becoming a very attractive synthesis technique in many areas of synthetic chemistry. In particular, the utilization of this method to fabricate nanostructured materials is a fast growing research area with immense potential. Similarly, the use of sacrificial scaffolds has been demonstrated as an effective route to achieve intricate 2D and 3D porous architectures. Here, we present an extremely fast and versatile synthetic approach based on microwave heating to fabricate complex macroporous magnetic frames using sacrificial templates. In just a few minutes, a stoichiometric and homogeneous conformal nanometric coating of superparamagnetic nanoparticles was grown onto a 2D monolayer formed by self-assembled polystyrene colloids. No post-treatment was required, the sacrificial polystyrene template was removed simultaneously as the magnetic nanoparticles formed, and large-scale structural order was preserved.

The fabrication of porous magnetic nanoarchitectures by microwave heating is reported. In addition to drastically decreasing the time for the synthesis, other characteristics of the technique, i.e. reaction kinetics, diffusivity and selectivity, have been exploited.

ParaCEST (Paramagnetic Chemical Exchange Saturation Transfer) agents offer an unparalleled opportunity to perform quantitative molecular imaging by MRI. Agents that can alter the image contrast they generate in response to changes in local environmental parameters such as pH, glucose concentration, or lactate concentration can be used ratiometrically to quantitatively describe the local tissue environment. However, when performing such quantitative measurements it is important that the results are not confounded by changes in a second environmental parameter. Pressure in vivo is far from uniform, varying both through the respiratory cycle and from tissue to tissue (tumors, in particular, have high interstitial pressures). Since paraCEST agents have positive activation volumes, their exchange kinetics and therefore the CEST effect that they generate are necessarily related to pressure. The purpose of this investigation was to examine whether the relatively small changes in pressure exhibited in vivo could affect CEST sufficiently to confound attempts to quantify other local environmental parameters. The CEST properties of a rigid EuDOTA-tetraamide was examined at temperatures ranging from 288 to 319 K, at applied pressures ranging from 0 to 414 kPa, and presaturation (B₁) powers ranging from 524 to 935 Hz. At no point was pressure found to affect the CEST generated by this chelate, which indicates that changes in in vivo pressure is unlikely to confound the quantitative measurement of physiologically relevant parameters by paraCEST MRI.

Interstitial pressure is an important physiological parameter that is often overlooked in molecular imaging. CEST is a method of generating MRI contrast that is acutely sensitive to changes in exchange and therefore possibly pressure. Variable pressure CEST experiments show that changes in interstitial pressure are unlikely to confound CEST MRI measurements.

Magnetic resonance imaging (MRI) is a powerful and noninvasive diagnostic technique of the human anatomy, physiology, and pathophysiology on the basis of superior spatial resolution and contrast. MRI is useful in providing anatomical and functional images of the human body. A large number of MRI techniques are performed employing gadolinium III [Gd^III] complexes to enhance image contrast by increasing the water proton relaxation rate in the body. Despite their wide and successful application in clinic, however, conventional Gd^III-based low-molecular weight contrast agents (CAs) are mostly extracellular contrast agents (ECCAs) exhibiting rapid extravasation from the vascular space. As a result, the time window for imaging is considerably reduced, thus limiting acquisition of high-resolution images. To overcome such limitations inherent to ECCAs, the necessity and the demand for the development of a new class of MRI CAs with functions including blood-pool and organ (or tumor)-targeting have risen recently. This microreview deals with our recent efforts on the design and the synthesis of new Gd-chelates and Gd nanoparticles (GdNPs) for use as blood-pool and organ/tumor-targeting MRI CAs. We also consider properties such as high r₁ relaxivity and high thermodynamic, kinetic, and biostabilities.

A new family of BPCAs and tumor-targeting MRI CAs are provided and characterized by a neutral Gd-chelate, [Gd(H₂O)(L)], where chelates (L) are DTPA-conjugates of ferrocenyldiamines (1), diaminobiphenyls (2), and DOTA-conjugates of tranexamates (3) and liver-targeting CAs by gold nanoparticles coated with GdL (Au@GdL). Tumor-targeting is achieved by GdL-RGD conjugation and GdO nanoparticles.

An efficient method for the synthesis of β-hydroxy and β-amino ketones from allylic alcohols catalyzed by Ru(η⁵-C₅Ph₅)(CO)₂Cl is described. The influence of the stereoelectronic properties of the catalyst on the reaction outcome has been studied. Optimization of the reaction conditions supressed the formation of undesired side products such as saturated ketones, benzyl alcohols, and α,β-unsaturated ketones. Several aromatic and aliphatic allylic alcohols have been reacted with a large variety of aldehydes or imines to produce β-hydroxy ketones or β-amino ketones, respectively, in yields up to 99 %. Based on experimental data, a mechanism via ruthenium alkoxides and ruthenium aldoxides is proposed. In addition, a C-bound ruthenium enolate has been characterized.

β-Hydroxy and β-amino ketones are synthesized from allylic alcohols and aldehydes or imines, respectively. The coupling reaction is catalyzed by Ru(η⁵-C₅Ph₅)(CO)₂Cl. Mechanistic investigations support a mechanism via ruthenium alkoxide intermediates.

The previous mechanistic studies of the Rh-mediated polymerization of carbenes suggests the involvement of organometallic compounds that have been derived from Rh(diene) species that contain a five-membered chelate ring of the type Rh{κ²-C,O-[–CH(COOR)–CH(Pol)–C(OR)=O–]} (Pol = polymer chain), which are characterized by the coordination of the β-ester group of the growing polymer chain to the metal. Herein we present our efforts to characterize the possibly related Rh^I(cod){κ²-C,O-[–CH(COOR)–CHR′–C(OR)=O–]} (cod = 1,5-cyclooctadiene) species. These structures can be generated by means of olefin exchange with an allyl complex and with the concomitant release of the corresponding 1,3-diene, which is derived from the allyl ligand. The product is unstable and further reacts by means of a bimolecular C–H activation process to form a related dinuclear complex [(cod)Rh(μ-{–CH(COOR)–CH–C(OR)=O–})₂Rh(cod)], in which the carbon dianion of the dimethyl or diethyl succinate bridges two Rh(cod) moieties. The complex was synthesized in an independent way and was structurally characterized. We investigated the importance of these complexes in carbene polymerization.

Rhodium chelate complexes where the β-ester group of the growing polymer chain is involved in backbonding to the metal are the predicted intermediates in the polymerization of the diazoesters. The Rh^I(cod) species of this type proved to be unstable and reacted by means of C–H activation to form dinuclear complexes. The implications for catalysis in the carbene polymerization reactions were investigated.

The oxidative addition of HF at trans-[Ir(Ar^F)(η²-C₂H₄)(PiPr₃)₂] (1a: Ar^F = 4-C₅NF₄; 1b: Ar^F = 2-C₆H₃F₂) affords the fluorido complexes trans-[Ir(Ar^F)(F)(H)(PiPr₃)₂] (2a: Ar^F = 4-C₅NF₄; 2b: Ar^F = 2-C₆H₃F₂). The hydrido fluorido complex 2a is also accessible by means of the reaction of the hydroxido complex trans-[Ir(4-C₅NF₄)(H)(OH)(PiPr₃)₂] (3a) with Et₃N·3HF. Both compounds 2a and 2b react with CO to give the carbonyl complexes trans-[Ir(4-C₅NF₄)(F)(H)(CO)(PiPr₃)₂] (4a: Ar^F = 4-C₅NF₄; 4b: Ar^F = 2-C₆H₃F₂). In the presence of traces of water, a slow reaction of 2a with CO₂ yields the hydrogencarbonato complex trans-[Ir(4-C₅NF₄)(H)(κ²-(O,O)-O₂COH)(PiPr₃)₂] (5a). Upon using 2a or 2b as fluorinating agent, Ph₃SiH could be converted into Ph₃SiF and CH₃C(O)Cl into CH₃C(O)F.

The oxidative addition of HF at trans-[Ir(4-C₅NF₄)(η²-C₂H₄)(PiPr₃)₂] affords the fluorido complex trans-[Ir(4-C₅NF₄)(F)(H)(PiPr₃)₂], which exhibits a square-pyramidal configuration. The latter reacts with acetyl chloride to yield acetyl fluoride and trans-[Ir(4-C₅NF₄)(Cl)(H)(PiPr₃)₂].

Paramagnetic lanthanide(III) complexes stable in aqueous solutions have gained increasing interest in the recent years due to their importance as contrast agents in magnetic resonance imaging (MRI). Lanthanide(III) complexes with macrocyclic ligands derived from 1,4,7,10-tetraazacyclododecane (cyclen) are widely used for the design of MRI probes because of their high thermodynamic stability and kinetic inertness. The rational design of more efficient contrast agents requires a better understanding of the structure and dynamics of these systems in solution. This contribution reviews the work of the author and his collaborators on the solution structure and dynamics of lanthanide(III) complexes with different cyclen-based ligands and closely related systems. DFT calculations provide molecular geometries and relative energies of the different stereoisomers of these complexes in good agreement with the experimental data. The conformational analysis performed with the aid of density functional theory (DFT) calculations was validated with the investigation of the Yb^III-induced ¹H NMR paramagnetic shifts, which encode information on the position of the observed NMR nuclei with respect to the Ln^III ion. Additionally, DFT calculations provide a better understanding of the dynamic processes responsible for the interconversion between the square-antiprismatic (SAP) and twisted-square-antiprismatic (TSAP) isomers of these complexes in solution, which might proceed through the inversion of the cyclen unit or the rotation of the pendant arms. The activation barriers obtained from theoretical calculations show a good agreement with the experimental values obtained from variable-temperature NMR spectroscopy. The work presented in this paper shows that DFT calculations in combination with NMR spectroscopy provide detailed information on the structure and dynamics of lanthanide(III) complexes at the molecular level and represent a powerful tool for the characterization of lanthanide(III) complexes relevant to the field of MRI contrast agents.

We present a short overview of the potential of DFT and paramagnetic NMR spectroscopy to explore the solution structure and dynamics of Ln^III complexes with cyclen-based ligands, providing information at the molecular level on the factors that affect the relative populations of square-antiprismatic (SAP) and twisted-square-antiprismatic (TSAP) isomers, as well as their interconversion mechanisms.

By using cost-efficient density functional theory accounting for dispersion in combination with an implicit solvent model, for the first time it has been possible to reproduce activation Gibbs free energies for phosphane dissociation from the Grubbs ruthenium olefin metathesis precatalysts in solution with good accuracy (mean unsigned error compared to experiment <2.5 kcal mol^–1). The barrier is calculated to be in the range 17.8–25.7 kcal mol^–1 for a set of nine catalysts, and is found to be located at intermediate Ru–P distances (ca. 4 Å). The agreement with the experimental activation parameters is gratifying and suggests that the calculations may give insight into these reactions and, in particular, offer resolution as to the individual components of the barriers. The forward (dissociation) barriers are much higher than the corresponding reaction free energies and the reverse reaction, phosphane binding, is associated with a significant barrier (13.2–15.6 kcal mol^–1). The latter barrier mainly arises from loss of entropy and solute–solvent dispersion interactions for the two fragments prior to Ru–P bond formation. Moreover, the fact that the barrier to phosphane binding is so significant means that the reaction free energy of phosphane dissociation cannot be taken to be identical or similar to the forward barrier, as has occasionally been assumed in earlier studies.

A DFT model validated against Ru–P bond energies from gas-phase MS experiments on Grubbs olefin metathesis catalysts also offers, in conjunction with an implicit solvent model, high accuracy for the corresponding dissociation barriers in solution. The accurate description is used to extrapolate information about the different components of the barriers.

Reaction of cis-Ru(κ²-OAc)₂(PPh₃)₂ with two-electron donor ligands L results in the formation of complexes trans-[Ru(κ¹-OAc)(κ²-OAc)L(PPh₃)₂] (L = CO, NO⁺, CNtBu). Vinylidene complexes (L = C=CHR) may be prepared from the corresponding reaction with terminal alkynes HC≡CR, and species containing hydroxyvinylidene ligands (L = C=CHCR¹R²{OH}) may be prepared from related reactions with propargyl alcohols HC≡CCR¹R²{OH}. Treatment of cis-Ru(κ²-OAc)₂(PPh₃)₂ with ω-alkynols HC≡C(CH₂)_nOH (n = 2–4) results in the formation of oxacyclocarbene complexes [L = CCH₂(CH₂)_nO]. An analysis of the spectroscopic data and the structural metrics (as determined by X-ray crystallography) of this series of complexes allows for the relative donor/acceptor properties of the ligand L to be evaluated. This comparison indicates that the vinylidene ligand behaves in a similar fashion to the isocyanide ligand.

The complex cis-[Ru(κ²-OAc)₂(PPh₃)₂] acts as a precursor for the formation of the complexes trans-[Ru(κ¹-OAc)(κ²-OAc)L(PPh₃)₂] where L is a two-electron donor, σ-donor/π-acceptor ligand. The structural and spectroscopic data of these species provide insight into the relative electron demand of the ligands L.

We report a cyano-bridged V–Nb bimetal assembly,K_0.59V^II_1.59V^III_0.41[Nb^IV(CN)₈]·(SO₄)_0.50·6.9H₂O, exhibiting ferrimagnetism with a high Curie temperature (T_C) of 210 K, which is the highest T_C value among those of octacyano-bridged bimetal assemblies. Such a high T_C value originates from the high coordination number of octacyanoniobate and the strong superexchange interaction between V^II (S = 3/2) and Nb^IV (S = 1/2) through the CN groups.

We prepared a V–Nb octacyano-bridged bimetal assembly, K_0.59V^II_1.59V^III_0.41[Nb^IV(CN)₈]·(SO₄)_0.50·6.9H₂O, with a high Curie temperature (T_C) of 210 K, which is the highest T_C among those of other octacyanometalate-based compounds. The high coordination number of octacyanoniobate and the strong superexchange interaction between V^II (S = 3/2) and Nb^IV (S = 1/2) through the CN groups are the reasons for such a high value.

Treatment of an arene–ruthenium dichloride dimer with thiols RSH to lead to cationic trithiolato complexes of the type [(arene)₂Ru₂(SR)₃]⁺ was shown to proceed through the neutral thiolato complexes [(arene)₂Ru₂(SR)₂Cl₂], which have been isolated and characterized for arene = p-MeC₆H₄iPr and R = CH₂Ph (1), CH₂CH₂Ph (2), CH₂C₆H₄-p-tBu (3), and C₆H₁₁ (4). The single-crystal X-ray structure analysis of the p-tert-butylbenzyl derivative 3 reveals that the two ruthenium atoms are bridged by the two thiolato ligands without a metal–metal bond. The neutral dithiolato complexes[(arene)₂Ru₂(SR)₂Cl₂] (1–3) are intermediates in the formation of the cationic trithiolato complexes [(arene)₂Ru₂(SR)₃]⁺ (5–7). Of the new [(arene)₂Ru₂(SR)₂Cl₂] complexes, derivative 2 is highly cytotoxic against human ovarian cancer cells, with IC₅₀ values of 0.20 μM for the A2780 cell line and 0.31 for the cisplatin-resistant cell line A2780cisR.

Treatment of p-cymene–ruthenium dichloride dimer with aliphatic thiols to give cationic trithiolato–diruthenium complexes was shown to proceed through the intermediacy of the corresponding neutral dithiolato complexes.

A vanadium 2,6-naphthalenedicarboxylate, V^III(OH)(O₂C–C₁₀H₆–CO₂)·H₂O, denoted as COMOC-3as (COMOC = Center for Ordered Materials, Organometallics and Catalysis, Ghent University), has been synthesized under hydrothermal conditions by means of both a solvothermal and a microwave synthesis procedure. The structure shows the topology of an aluminium 2,6-naphthalenedicarboxylate, the so-called MIL-69 (MIL = Materials of the Institute Lavoisier). After calcination at 250 °C in air, the V^III center was oxidized to V^IV with the structure of V^IVO(O₂C–C₁₀H₆–CO₂) (COMOC-3). The oxidation process was verified by cyclic voltammetry and EPR spectroscopy. The crystallinity was investigated by variable-temperature XRD. The title compound is stable against air and moisture. The catalytic performance of COMOC-3 was examined in the liquid-phase oxidation of cyclohexene. COMOC-3 exhibited similar catalytic performance to MIL-47 [VO(O₂C–C₆H₄–CO₂)]. The compound is reusable and maintains its catalytic activity through several runs.

A vanadium-based metal–organic framework (COMOC-3) has been synthesized and fully characterized. It crystallizes in the monoclinic system with the space group C2/c (no. 15). This closed MIL-69 analogue shows excellent thermal stability and good catalytic performance in the liquid-phase oxidation of cyclohexene. The catalyst can be regenerated and reused without significant loss of activity.

We report the synthesis and characterization of the first ferrocenyl polyphosphane incorporating six phosphorus donor atoms. In this unique ligand, the cyclopentadienyl rings of the ferrocenyl backbone adopt a staggered position, which leads to a piano-stool arrangement for each of the two sets of three P atoms facing the same direction. As a consequence of its remarkable flexibility, this hexaphosphane displays versatile coordination behaviour towards metals, leading to unexpected structures of palladium and platinum bimetallic complexes. Analogous molybdenum and rhodium complexes are more classical.

The synthesis of the first hexadentate ferrocenyl polyphosphane, 1,1′,2,2′,4,4′-hexakis(diphenylphosphanyl)ferrocene (Hexaphosphine), is reported. The versatile coordination of this polydentate ligand was established by the formation of surprising binuclear group 6, 9 and 10 transition metal complexes.

The acylhydridorhodium(III) complex [RhHCl{PPh₂(o-C₆H₄CO)}(py)₂] (1) reacts with 8-quinolinecarbaldehyde (C₉H₆NCHO) to afford mixed diacyl [RhCl(C₉H₆NCO){PPh₂(o-C₆H₄CO)}(py)] (2) with acyl groups trans to chlorine and to pyridine. Complex 1 undergoes displacement of pyridine by 2-(aminomethyl)pyridine (ampy) or diphosphanes to give hydridoacyl neutral [RhHCl{PPh₂(o-C₆H₄CO)}(LL)] [LL = ampy (3), bis(diphenylphosphanyl)methane (dppm, 5), 1,3-bis(diphenylphosphanyl)propane (dppp, 6), 1,2-bis(diphenylphosphanyl)ethane (dppe, 7)] with hydride trans to chloride. Complex 3 exchanges hydride with chloride to give [Rh(Cl)₂{PPh₂(o-C₆H₄CO)}(ampy)] (4). The reaction of 2 with bidentate N-donor ligands yields cationic mixed diacyl [Rh(C₉H₆NCO){PPh₂(o-C₆H₄CO)}(NN)]⁺ species [NN = 2,2′-bipyridine (bipy, 8), ampy (9)]. Neutral or cationic diacyl complexes that contain two acylquinoline fragments can be obtained by the reaction of dimer [Rh(μ-Cl)(C₉H₆NCO)₂]₂ (10) with pyridine to give [Rh(Cl)(C₉H₆NCO)₂(py)] (11) or with bidentate N- or P-donor ligands (LL) to afford [Rh(C₉H₆NCO)₂(LL)]⁺ [LL = dppm (12), dppe (13), dppp (14), 1,4-bis(diphenylphosphanyl)butane (15), ampy (16), 8-aminoquinoline (17), biacetyldihydrazone (18), bipy (19)] with the acyl groups trans to LL. Complex 11 is highly fluxional in solution. At low temperatures, the acylquinoline chelate opens to allow an intramolecular exchange between 11a and 11b (ΔH^‡ = 10.1 ± 0.2 kcal mol^–1 and ΔS^‡ = 1.0 ± 0.1 cal K^–1 mol^–1), and pyridine dissociation occurs at room temperature. All the complexes were characterized spectroscopically. Single crystal X-ray diffraction analysis was performed on 2.

Hydridoacylrhodium(III) (1) reacts with chelating ligands to afford new neutral acylhydrido complexes with hydride trans to chloride. The reaction with 8-quinolinecarbaldehyde affords a diacyl compound, which may give cationic diacyl derivatives with donor atoms trans to the acyl groups.

Thermally driven heat pumps can significantly help to minimize primary energy consumption and greenhouse gas emissions generated by industrial or domestic heating and cooling processes. This is achieved by using solar or waste heat as the operating energy rather than electricity or fossil fuels. One of the most promising technologies in this context is based on the evaporation and consecutive adsorption of coolant liquids, preferably water, under specific conditions. The efficiency of this process is first and foremost governed by the microporosity, hydrophilicity, and hydrothermal stability of the sorption material employed. Traditionally, inorganic porous substances like silica gel, aluminophosphates, or zeolites have been investigated for this purpose. However, metal–organic frameworks (MOFs) are emerging as the newest and by far the most capable class of microporous materials in terms of internal surface area and micropore volume as well as structural and chemical variability. With further exploration of hydrothermally stable MOFs, a large step forward in the field of sorption heat pumps is anticipated. In this work, an overview of the current investigations, developments, and possibilities of MOFs for use in heat pumps is given.

This review introduces metal–organic frameworks (MOFs) as a promising new class of microporous materials for use in adsorption heat transformation applications. The water adsorption characteristics of several MOFs are summarized, including heat of adsorption and cycle stability, which show the tremendous potential of MOFs in thermally driven heat pumps.

Synthetic routes to cationic group 4 metallocene–(o-phosphanylaryl)oxido compounds of the type [Cp^R₂M(OPR₂)][WCA] (M = Ti, Zr, Hf; WCA = weakly coordinating anion) are described. The neutral mono-methyl complexes [Cp^R₂ZrMe(OPR₂)] 1–6 [Cp^R = Cp (1–3) or Cp* (4); OPR₂ = o-OC₆H₄(PtBu)₂ (1 and 4), OCMe₂CH₂(PtBu)₂ (2) or OC(CF₃)₂CH₂(PtBu)₂ (3)] are prepared by protonolysis of [Cp^R₂ZrMe₂] by the parent alcohol. The remaining methyl group in such complexes is best removed by protonolysis with [DTBP][B(C₆F₅)₄] (DTBP = 2,6-di-tert-butylpyridinium) to yield the desired cationic complexes 7 and 8 in the case of 1 and 4. In the case of 2 and 3, this method leads to side reactions. Treatment with B(C₆F₅)₃ yields the desired cations in all cases; however, side reactions with the generated [MeB(C₆F₅)₃] anion in subsequent reactions leads to problems. Hafnium analogues may be synthesised by similar routes. In the case of titanium, a different method must be adopted: chloride abstraction using [Et₃Si][B(C₆F₅)₄] from the parent complex [Cp₂TiCl(OPR₂)]. Such cationic group 4 metallocene–(o-phosphanylaryl)oxido compounds exhibit reactivity that is best described by the frustrated Lewis pair concept.

Synthetic routes to transition-metal-containing frustrated Lewis pairs based on cationic group 4 metallocene–(o-phosphanylaryl)oxido compounds [Cp^R₂M(OPR₂)][WCA] [Cp^R = Cp or Cp*; OPR₂ = o-OC₆H₄(PtBu)₂, OCMe₂CH₂(PtBu)₂ or OC(CF₃)₂CH₂(PtBu)₂; M = Ti, Zr, Hf; WCA = weakly coordinating anion) are described.

The synthesis and characterisation of four new Schiff base-like ligands with long alkyl chains in the outer periphery and their iron(II) complexes with methanol and pyridine as axial ligands is reported. Two of the methanol complexes crystallise in a lipid layer-like arrangement with the alkyl chain (tail) packed in the middle and the iron centres (head) in the outer sites. The pyridine complexes show varying types of spin transition (step wise, incomplete, with hysteresis), which depends on the alkyl chain length and substituents in the outer periphery of the ligand. Investigations in solution using ¹H NMR spectroscopy demonstrate that the differences in the spin transition behaviour are due to packing effects as the same transition curve is obtained independently of the alkyl chain length.

A series of iron(II) complexes with head–tail character have been investigated. Lipid layer-like structures have been observed,and the complexes with pyridine show spin crossover behaviour.

Reactions of [{Cp*IrCl(μ-Cl)}₂] (Cp* = η⁵-pentamethylcyclopentadienyl) with bidentate pyridine–imine ligands such as 2-(1-hydrazonoethyl)pyridine (L¹-NH₂) and 4-({[1-(pyridine-2-yl)ethylidene]hydrazono}methyl)benzaldehyde (L³-CHO), followed by salt exchange, afforded the corresponding iridium mononuclear complexes [Cp*IrCl(L¹-NH₂)][PF₆] (1a-PF₆) and [Cp* IrCl(L³-CHO)][PF₆] (6-PF₆) that bear N-amino and formyl functionalities, wh