Structural trends in one and two dimensional coordination polymers of cadmium(II) with halide bridges and pyridine-type ligands

Cadmium dihalides were reacted with pyridine derivatives as Lewis bases, and the solid state structures of 15 reaction products were studied by X-ray diffraction; all but one of these structures are reported for the first time. Among the 15 complexes there are 13 coordination polymers containing six-coordinated cadmium with four bridging halides in the equatorial and two pyridine ligands in the axial positions of a pseudo octahedron. For unidentate ligands such as pyridine and 3-chloro-, bromo- or methylpyridine chain polymers of composition [CdX2( L)(2)](1)(infinity) were formed. The six combinations of Cl, Br, or I as bridging halides with 3-halopyridine and the two of chloride and bromide bridges with 3-methylpyridine lead to eight isomorphous compounds in the space group P2(1)/c. In a second structure type 4,4'-bipyridyl was used to link neighbouring chains to two-dimensional nets with [CdX2( bpy)](2)(infinity) stoichiometry. The chloro and bromo derivatives are isomorphous and crystallise in a space group Pban whereas the iodide bridged complex was obtained in the supergroup Cmmm. The halogen substituted pyridines represent the most versatile ligands for the formation of coordination polymers - they can be accommodated in the whole range of halide bridged [M(mu-X)(2)](1)(infinity) chains (M = Zn, Cd) covering metal. metal distances between 3.654 and 4.143 Angstrom. In contrast to the above mentioned halide bridged topologies terminal rather than bridging iodide ligands occur in [CdI2(py)(2)] and [CdI2(3-Mepy)(2)]: these complexes are mononuclear with the metal center in tetrahedral coordination.