Synthesis and Single Crystal Structure Characterization of Dinuclear and Polymeric Mixed‐ligand Coordination Compounds of Zinc(II) and Cadmium(II) with the Bridging Ligand 1,2‐Bis(pyridin‐4‐ylmethylene)hydrazine

Three d10-transition-metal coordination compounds [Cd(tfpb)2(4-bpmh)]n (1), [Cd(9-aca)(NO3)(OHCH3)(4-bpmh)]n (2) and [Zn2(dpp)4(4-bpmh)] (3) with the bridging ligand 4-bpmh were synthesized [4-bpmh = 1,2-bis(pyridin-4-ylmethylene)hydrazine, tfpb = 4,4,4-trifluoro-1-phenylbutane-1,3-dionate, 9-aca = anthracene-9carboxylate, dpp = 1,3-diphenylpropane-1,3-dionate]. Compounds 1– 3 were characterized by FT-IR spectroscopy, elemental analysis, and structurally authenticated by X-ray crystallography. Compounds 1–3 are constructed by an O,O -donor ligand including chelating β-dike-

This results show that the rational choice of organic ligands in combination with 4-bpmh for the design and construction of mixed ligand base coordination compounds with structural and functional diversity is especially challenging. 4-bpmh has been used to generate new coordination compounds with Zn 2+ and Cd 2+ containing diverse organic ligands where β-diketones are not included. β-diketones has been found to be able to coordinate to the transition metal ions through the chelation of two oxygen atoms of the enolate anion to give tris-and tetrakis(β-diketonato) metal coordination compounds [41][42][43][44][45]  replacement of the C-H bonds with C-F, (fluorinated β-diketonates) makes the β-diketonate unit easier to coordinate with a metal ion and forming an extended conjugated system. For example, an electron-withdrawing perfluoroalkyl group reduces the electron density on the oxygen atoms of β-diketones, and the acidity of the enolic form of these β-diketones is further increased and thereby increasing the Lewis acidity of the metal center in the ensuing metal coordination compound.
Therefore, varying the substituents in β-diketones may cause major changes in the complexes properties like the reactivity against other organic ligands. [46] Typically, the coordination sphere of the metal ion in this case consists of solvent or water molecules, which can be replaced by a variety of mono-or bidentate N,O,S,P-donor ligands. Therefore, beside the β-diketones, one neutral bidentate N,N-donor linker as a synergic ligand can be a very efficient for manufacturing new multidimensional structures since it completes the inner coordination sphere by binding itself to the metal ions, and keeps the solvent molecules away from the vicinity of the metal ions. [47][48][49] Therefore, research on the coordination chemistry of β-diketones/4-bpmh is interesting for constructing novel coordination compounds and understanding topology control.
Cd 2+ and Zn 2+ ions have five and six coordinated geometries with octahedral, trigonal bipyramid and square pyramid.

Structure of [Cd(tfpb) 2 (4-bpmh)] n (1)
Compound 1 crystallizes in the triclinic P1 space group (see Table S2 for details, Supporting Information). The asymmetric unit contains one half-occupied Cd 2+ ion on an inversion center, one tfpb and half a 4-bpmh ligand (with an inversion center Z. Anorg. Allg. Chem. 2020, 1861-1868 www.zaac.wiley-vch.de at the middle of the N-N hydrazine bond). As illustrated in Figure 2, the Cd 2+ center is ligated by four O atoms from two inversion-symmetry-related chelating tfpb ligands and two N donor atoms from two trans 4-bpmh linkers in a near octahedral coordination geometry. The Cd-N1 bond length is 2.368(9) Å, while the Cd-O1 and Cd-O2 bond lengths are essentially identical with 2.252(7) and 2.256 (7)  The chains assemble in parallel fashion which neighboring chains being shifted by half of 4-bpmh with respect to each other. There is an interchain hydrogen bonding interaction between an oxygen atom from the diketonate group as acceptor and C-H group from pyridine ring as donor and also short interchain π···π interactions, [53][54][55] between the diketonate phenyl rings, and interchain C-F···π interactions ( Figure 3). Figure 4 shows the crystal packing of 1 along the crystallographic a axis. The detailed analysis of short interactions is described in Tables S5, S6, and S8 (Supporting Information).

Structure of [Cd(9-aca)(NO 3 )(OHCH 3 )(4-bpmh)] n (2)
Single crystal X-ray diffraction analysis reveals that 2 crystallize in monoclinic P2 1 /c space group (see Table S2 for de-Z. Anorg. Allg. Chem. 2020, 1861-1868 www.zaac.wiley-vch.de tails, Supporting Information). The asymmetric unit of 2 comprises of one kind of Cd 2+ ion, one 9-aca that displays as a monodentate ligand, one 4-bpmh bridging linker, one methanol solvent molecule and a monodentate nitrate ion. As illustrated in Figure 5, the Cd 2+ center is five-coordinate adopting distorted trigonal bipyramid coordination geometry (TBP). Cd 2+ center is ligated by three different O atoms in the equatorial position belong to the deprotonated carboxyl group of 9-aca, neutral methanol and anion nitrate (O2, O1, and O4) and two N atoms from two trans-positioned 4-bpmh ligands at axial positions with N2-Cd1-N5 angle of 165.30 (4)°( Figure 5). The presence monodentate 9-aca and nitrato groups were established by IR and X-ray single crystal analysis in 2. The pick positions of asymmetric and symmetric stretching vibration band of ν(C=O) group is shifting to the lower frequencies after the formation of the polymer, [56,57] and ν asym and ν sym frequencies appeared at 1581, 1367 cm -1 (Δν asymν sym = 214), corresponding to the carbonyl functionality of the 9-aca ligand and suggesting a monodentate mode with the Cd-O bond length 2.446(2) Å. The C-O distance for the single bond is 1.423(3) Å, while the C-O distance for the C-O double bond length is 1.283(3) Å. The IR vibrations of nitrate ion with a monodentate binding feature appeared at 1290 cm -1 for ν sym (NO 2 ) with very strong intensity, 1060 cm -1 for ν sym (NO 2 ), 1000 cm -1 for ν(NO), and then 739 cm -1 for δ sym (NO 2 ) with very strong intensity. [58,13] Selected bond lengths and bond angles for the crystal structure of 2 are given in Table S3 (Supporting Information). The Cd1-N2 and Cd1-N5 bond lengths is 2.1297(17) and 2.0904(18) Å respectively while the Cd1-O1, Cd1-O2 and Cd1-O4 bond lengths are 2.3519(18), 2.4457(17) and 2.601(2) Å. It was found that bond length of Cd-O is notably long (ϳ2.6 Å) indicating a reduced bond valence. [59] According to the VSEPR theory of molecular geometry, an axial position is more crowded because an axial atom has three neighboring equatorial atoms at a 90°bond angle, whereas an equatorial atom has only two neighboring axial atoms at a 90°bond angle and also an equatorial position has two neighboring equatorial atoms at a 120°bond angle. [27] The bulky and sterically hindered 9-aca tended to occupy an equatorial position in monodentate coordination mode along with a methanol and a monodentate nitrate ion therefore, the plane of trigonal con-ARTICLE sist of three oxygen atoms. The axial positions were occupied by two 4-bpmh which connect metal centers. Therefore, the least electronegative ligands occupy the axial position. But, according to the VSEPR theory of molecular geometry, the axial positions tendency to be occupied by linkers which has a greater electronegativity and pi-electron withdrawing. Hence, a combination of increase in electronegativity and steric hindrance/steric reduction may be responsible for the structural representation found by 2.
A simplified view of 2 shows, the structure consists of neutral infinite chains of cadmium atoms linked by 4-bpmh bridge that the Cd···Cd distance is 14.794 Å. The overall 1D chain can be easily considered to have sine-wave shape and the complex molecular fragment is [Cd(μ-4-bpmh)(9-aca)(OHMe)(NO 3 )]. Figure 6 shows the crystal packing of 2 along the crystallographic c axis. In addition, the dihedral angle of two pyridine rings of 4-bpmh is 13.456° (6). Selected torsion angles for the crystal structure of 2, are given in Table S4 (Supporting Information). The study of the crystal packing of 2 revealed the chains pass through each other like a wave and the stacking of the chains leads to the formation of a channel-like structure filled by anthracene ring along the a crystallography axis. There is a stronger hydrogen bonding interaction between nitrate group as acceptor and O-H group from methanol as donor and also two weaker hydrogen bonding interactions in which pyridine ring donate hydrogen-bonds through carbon hydrogen have been detected (Figure 7). We can not find any other effective short interactions. The detailed analysis of short interactions was described in Table S5 (Supporting Information).

Conclusions
Using cadmium(II) nitrate, cadmium(II) acetate, and zinc(II) acetate in appropriate combination with one of the three O,OЈdonor (tfpb, dpp and 9-aca) ligands and one linear neutral bridging N,NЈ-donor ligand (4-bpmh, secondary ligand), the new coordination compounds [Cd(tfpb) 2 (4-bpmh)] n (1), [Cd(9aca)(NO 3 )(OHCH 3 )(4-bpmh)] n (2), and [Zn 2 (dpp) 4 (4-bpmh)] (3) were successfully synthesized under the same experimental conditions. Their single crystals have been grown via branched tube technique and then analyzed by X-ray crystallography. Due to the different shapes, sizes, and coordination abilities of the ligands and metal ions, the metal coordination compounds have different structures. Of N,NЈ-donor ligand (4-bpmh) has been investigated in this study, two 1D polymers (1 and 2) and a dimeric complex (3) formed. 4-bpmh appeared as a bridge ligand in all three structures and O,OЈ-donor ligands probably affect the formation of the final structures. The distances between the pyridyl-nitrogen atoms in the 4-bpmh molecule of 11.358 Å for 1 and 10.658 Å for 2 result in a linear and sinewave 1D chain polymeric topologies respectively. The introduction of fluorine-containing substituents into the β-diketone fragment resulted in the structural changes of a dinuclear coordination complex in 3 to one-dimensional coordination polymer in 2. This is probably linked to the higher acidity of the enolic form of fluorinated β-diketonate ligands compared to phenyl-substituted β-diketonate which causes the electronic demands of the coordinate. These different structures indicated that the coordination behaviors of metal ions and the coordination modes, different steric hindrances of aromatics played important roles in the construction of final coordination compounds. This study indicates that it is possible to explore interesting aesthetic multi-dimensional structures with chelating βdiketonates along with different neutral N,NЈ-donor ligands.

Experimental Section
Synthesis: The title coordination compounds 1, 2, and 3 were synthesized from a mixture of one of the metal salts Cd(OAc) 2 (0.1 mmol), Cd(NO 3 ) 2 or Zn(OAc) 2 (0.1 mmol) with 4,4,4-trifluoro-1-phenylbutane-1,3-dionate (tfpb) (0.2 mmol), anthracene-9-carboxilate (9-aca) (0.2 mmol) or 1,3-diphenylpropane-1,3-dionate (dpp) (0.2 mmol) and 1,2-bis(pyridin-4-ylmethylene)hydrazine as an auxiliary ligand (4-ARTICLE bpmh) (0.05 mmol) (Scheme 2) in a metal-to-ligand ratio of 1:2:0.5 in methanol using a T-tube glass. Figure 1 shows a perspective drawing of the T-tube glass applied. Dried methanol was carefully added to the mixture of starting materials until the arm of the T-tube was completely filled. The tube was sealed and left in an oil bath at 65°C under silent environment, while the arm was kept at room temperature. Yellow, red and yellow single crystals from 1, 2, and 3, respectively, grew in the cold arm of the tube over a period of one week. Suitable crystals were carefully selected, covered with protective oil and mounted on cryo loops for X-ray analysis. More information about the experimental procedures, instruments used, characterization data and structural characterization of 1-3 are provided in the Supporting Information.

Structure Analysis and Refinement:
Single crystal X-ray diffraction experiments were performed with protective-oil coated crystals in a cooling gas stream of dry nitrogen [140(2) K] on a Bruker Kappa APEX II CCD diffractometer (Bruker AXS Inc., Madison, WI, USA) [62] with Mo-K α radiation (microfocus tube, multi-layer mirror system, λ = 0.71073 Å) applying ω-scans. SMART. [63] SAINT [63] and SADABS [64] were used for the calculations of data collection/unit cell refinement, frame integration/data reduction and multi-scan absorption correction, respectively. Maximum and minimum transmission factors are listed in Table S2 (Supporting Information) along with crystal data and further details of data collections and structure refinements.
In the case of 1 the symmetry of the diffraction pattern was compatible with the anorthic space group types P1 and P1. The latter was favored with respect to the value of |E 2 -1| and proved to be the correct one in the course of structure refinement, finally. In case of 2 and 3 space group P2 1 /c and P2 1 /n, respectively, was uniquely determined from symmetry and systematic extinctions. Primary structure solutions was achieved by direct methods with SHELXS-97, [65] completion of the structural models including the positions of the hydrogen atom of the hydroxyl group of the coordinating methanol molecule in 2 and most of the other hydrogen atoms in 1-3 by subsequent difference-Fourier syntheses calculated with SHELXL-2017. [66] Structure solution with direct methods was not straightforward in the case of 1 and 2, and subgroup P1 and P1, respectively, was used for solution, followed by transformation to the higher symmetry true space group. [67] Refinement was done by full-matrix least-squares calculations on F 2 using SHELXL-2017 [66][67][68] In the case of 2 the positions of the H atom of the OH group of the methanol ligand and the H atoms at the imino group carbon atoms C22 and C23 were refined. For all other H atoms in 1, 2, and 3 the riding model was applied using the program's default idealized C-H bond lengths and N-C-H, C-C-H and H-C-H bond angles where applicable. In addition, the H atoms of the methanol ligand's CH 3 group in 2 were allowed to rotate collectively around the adjacent C-O bond axis. The U iso (H) values were set to 1.5U eq (O hydroxyl ), 1.5U eq (C methyl ) and 1.2U eq (C any CH group ).
Stabilization of the structural model using appropriate geometrical and anisotropic displacement parameter restraints was needed in the case of 2, only. In the bridging ligand the pyridyl group containing N5 was subjected to same distance restraints for all C-C bonds. Same distance restraints were also used for C-C bonds of the anthracenyl group of the carboxylate ligand and individual bond lengths restraints were applied for C2-C3, C4-C9 and C11-C16 in this ligand. Finally, all atoms of the anthracenyl group were constrained to be coplanar within the default standard uncertainty, and default "rigid bond" and same U ij components restraints were applied to the atoms of these group. The crystal structure of 3 was shown to contain solvent accessible voids with a volume of 110 Å 3 . However, attempts to introduce water molecules to account for some unspecific residual electron density in this region did not result in converging refinement and significant improve-Z. Anorg. Allg. Chem. 2020, 1861-1868 www.zaac.wiley-vch.de ment of reliability factors and contribution to |F calc | 2 was supposed to be negligible.
In the case of 1 after final refinement the difference electron density map showed residual electron density maxima Ͼ 1 e-Å -3 in physically not reasonable positions along with several values of |F obs | 2 ϾϾ |F calc | 2 indicative for unaccounted twinning. Further inspection of the intensity data gave evidence that the crystal under investigation had been suffering from non-merohedral twinning [69] with the twin axis defined as the one parallel to the b* axis of the anorthic reciprocal unit cell. The twin law (as a rotation matrix written by rows: -1 0 0 -0.789 1 -0.311 0 0 -1) was calculated using the TwinRotMat routine implemented in PLATON and a HKLF5 format data file was created, [67] that allowed for a second, improved refinement assuming the additivity of reflection intensities of the twin components. [70] The twin fraction was refined to 0.76(2)/0.24 (2). Graphics of 1, 2, and 3 were prepared with DIAMOND. [71] Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies of the data can be obtained free of charge on quoting the depository numbers CCDC-1994296 (1), CCDC-1991336 (2), and CCDC-1991214 (3) (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac. uk, http://www.ccdc.cam.ac.uk)