Chemistry - A European Journal

The design of the first π-conjugated organic polymer with magnetic ordering (an example of which is shown here) was based upon synthesis and study of polyarylmethyl polyradicals with increasing number of exchange-coupled unpaired electron spins.

A variant of associative ligand substitution in Pd, which operates in 1, is observed in the transmetalation step under the conditions of the Pd-catalyzed coupling of organic halides or triflates and stannanes (Stille reaction). Dissociative transmetalation pathways can be discounted. Genuine 14-electron intermediates (C) are still to be detected spectroscopically, and their contribution to transmetalation in the Stille reaction, as well as that of solvent complexes E under the usual conditions, is negligible.

A statistical analysis of the crystal structures of 61 p-tert-butylcalix[4]arene derivatives coupled with molecular mechanics calculations (with periodic boundary conditions) shows how the presence of a guest affect the description of the crystal.

Studies of a cyclic {Ni₁₂} wheel (shown here) show that it has an S=12 ground state. The compound shows magnetic hysteresis and quantum tunnelling when studied at low temperature, proving it is a single molecule magnet. Inelastic neutron scattering has allowed us to derive three exchange interactions to explain the very high ground state.

Thymine does it! A range of modified oligonucleotides was prepared bearing a covalently attached pyrenyl group located outside the DNA base stack. The injection of excess electrons into DNA upon photoexcitation was then investigated spectroscopically using the pyrenyl-modified DNA duplexes. It was possible to show that electron transfer can occur from the Py-dU group only to adjacent thymines (see scheme).

Unusual sorption properties have been found in a new series of layered metal phosphonate materials (see illustration) containing more than one metal within the (MO₃P) structural backbone. The mixed copper–zinc vinylphosphonate materials investigated are shown to exhibit tunable intercalation of amines by variation of the copper:zinc ratio within the structure.

The tetracyanoethylene radical anion, [TCNE]^.−, forms diamagnetic π dimers, π-[TCNE]₂²⁻ (see figure), with intradimer separations ∼2.9 Å. Albeit long with respect to conventional CC bonds, the bonding interaction is attributed to two-electron four-center bonding arising from π*–π* overlap by the cation–anion interactions present in the crystal. Crystallographic as well as spectroscopic (IR and UV-visible) features of this bonding are observed.

Charge-solvation complexes CS1 in which the K⁺ ion interacts with the carbonyl oxygen atoms of the dipeptide backbone (see scheme) are the most stable among the 11 potassium complexes of glycylglycine (R=H) or alanylalanine (R=Me) studied here; these were identified by a combination of Monte Carlo conformational searching and density functional calculations. The absolute stabilities and geometries of all complexes are reported.

The gas-phase acidities of HCP, CH₃CP (see scheme), and CH₃CAs have been measured by means of Fourier Transform Ion Cyclotron Resonance (FTICR) mass spectrometry and calculated at the CCSD(T)/6-311+G(3df,2p)//QCISD/6-311+G(df,p) level of theory. Quite unexpectedly, while HCP and HCAs are found to be weaker acids than HCN, the opposite trend is found for the corresponding methyl derivatives, the acidity of which increases as CH₃CN<CH₃CP<CH₃CAs.

An unprecedented family of isolable dicarbonyl compounds with formula cis-[M^II(C₆F₅)₂(CO)₂] for all three Group 10 metals (M = Ni, Pd, Pt) has been prepared. The Ni^II member is a thermally unstable species that easily decomposes by undergoing a reductive elimination process (see scheme).

Molecular logic behaviour can be recognized in the behaviour of everyday ion indicators or newly designed versions which interact with two ions. Furthermore, these simultaneously show multiple logic configurations. One integrated receptor₁–ICT chromophore–receptor₂ system is depicted.

Increasing conformational preorganisation in the flexible side arms (see scheme) of a tripodal host leads to increased selectivities towards guests anions (chloride > bromide > nitrate).The receptors described have the same binding topology, although they differ in the level of conformational preorganization.

Mixing silver(I) salts with a readily prepared pyridylimine ligand (see scheme) gives coordination polymers, the tacticity of which is controlled by different twisting motifs within the ligand. The isotactic helical isomer contains metal centres ordered along two vectors in a 2×n grid arrangement.

Binding of the pendant arm containing a dansylamide group to the metal center in the nickel(II) complex of a cyclam-like macrocycle is pH controlled. The binding detachment of the pendant arm to/from the Ni^II center is signaled by changes in the emission properties of the dansyl subunit in the side chain; its fluorescence is high when the pendant arm is not coordinated and low when the sulfonamide group is bound to the metal (see scheme).

Three octahedra and one trigonal prism that share faces in a (TP-O_h-O_h-O_h)₂ sequence constitute the framework of the new one-dimensional oxide [Sr₁₀(Sr_0.5Rh_1.5)_TP(Rh₆)_Oh]O₂₄, the (α=3 β=2) member of the (A₃A′BO₆)_α (A₃B₃O₉)_β homologous series. A high-resolution electron microscope image and a schematic diagram of the structure is illustrated here.

Different metallation/protonation behaviour of peptide helices and strands has been observed by electrospray ionization mass spectra and ab initio theoretical studies. The results suggest that metallation in helices is favoured by chelation to carbonyl groups at the C-terminus, while in strands metallation/protonation occurs at isolated carbonyl groups (see figure).

A new Fe^IIspin transition material displaying a wide memory effect domain is reported. Insights on the origin of its pronounced cooperative effects are outlined. The Fe^II-1,2,4-triazole chain compound shows a very wide and fully reproducible hysteresis loop (48 K), centered around 145 K as depicted, which is the widest hysteresis loop ever reported for such a compound.

Twist or bend? Trisubstituted alkenes 1 and 2 are forced into this dilemma by steric strain. Their structures show a delicate balance between various angle distortions, but they generally prefer bending over twisting.

Producing chiral drugs in a single enantiomeric form is of great importance to the pharmaceutical industry. A new high-resolution solid-state NMR method allows racemates and enantiomers to be distinguished by making use of the fact that their molecular symmetries and packing are usually significantly different.

Novozym-435 has been found to be an effective biocatalyst for the kinetic resolution of a series of racemic 2,3-allenols, affording highly optically active (S)-(−)-2,3-allenols and (R)-(+)-2,3-allenyl acetates in high yields and with excellent ee values (see scheme).

The calculation of the potential energy surfaces of the dinuclear mixed-valence species containing [MnO₂Mn]ⁿ⁺ (n=1,3; see picture) allowed the classification of these systems according to the extent of valence localization as Class II compounds, in the Robin–Day classification scheme. The variation of the squared overlap integrals between the magnetic orbitals was used to rationalize the trend of J values computed on passing from the Mn^II/Mn^II to Mn^IV/Mn^IV systems. The magnetic orbitals were directly obtained from the eigenvectors of the broken symmetry state.

The coordination polymer network allows the formation of metallogels that exhibit catalytic properties. The metallogels are obtained in dimethylsulfoxide by using transition-metal ions with multiple sites available for coordination and multidentate ligands such as 1 (see scheme).

Simply adding a chiral drug, such as naproxen (A21), makes all the difference in the Ti-catalyzed hetero-Diels–Alder reaction of Danishefsky's diene with aldehydes in terms of both efficiency and enantioselectivity. The additive accelerating phenomenon and positive nonlinear effect discovered in the catalytic system combined with successful isolation of stable heterochiral (L1)₂Ti complex provided a further insight into the understanding of the asymmetric induction mechanism.

The role of fluoride in the Tamao oxidation of a model dialkoxysilane has been analyzed by computational means. A potential energy surface was calculated consistent with the typical synthetic methods required for the conversion of alkoxysilanes to alcohols; fluoride generates reactive fluorosilicates that undergo rearrangement upon attack by hydroperoxide anions (see scheme).