Coordination polymers based on cadmium(II) pyridine complexes: synthesis, range of existence, and structure

A series of nine new cadmium compounds of formal composition [Cd(mu-X)(2)py(2)] (X = Cl, Br, I; py=3,5-disubstituted pyridine ligands with methyl, chloro, and bromo substituents) were synthesized and characterized by single crystal X-ray diffraction. Only for the combination of the sterically most demanding ligands, namely I and 3,5-dimethylpyridine, is a mononuclear tetrahedral complex obtained; in in all other eight cases one-dimensional coordination polymers are found. In these chains cadmium(II) cations are linked in an edge-sharing fashion by halogen bridges in their pseudoequatorial plane, with terminal pyridine ligands completing the pseudo-octahedral coordination sphere. In all polymers the distance between neighboring Cd atoms corresponds to the shortest lattice constant: metal metal separations systematically depend on both bridging and terminal ligands and range between 3.77 and 4.14 Angstrom. This intermetal distance and the coordination mode of the donor ligands are found to be correlated. Five of the Cd chain polymers adopt the structure type found for [Zn(mu-Cl)(2)py(2)(infinity) over bar]. In addition to previous work the zinc derivatives [ZnX2 (3,5-Me(2)py)(2)] (X = Cl, Br) were investigated for comparison and shown to be mononuclear.