SYNTHESIS AND STRUCTURES OF THE BIS(CIS-1-METHYLTHIOSTILBENE-2-THIOLATE) OF CADMIUM AND ITS ADDUCTS WITH DIMETHYL-SULFOXIDE, 4-(DIMETHYLAMINO)PYRIDINE, AND 2,2'-BIPYRIDYL - HEXACOORDINATION OF CADMIUM VS PENTACOORDINATION IN THE CORRESPONDING ZINC DERIVATIVES

Whereas the zinc derivative of cis-1-methylthiostilbene-2-thiol forms a well-defined mu-S-bridged dimer of composition Zn2[Ph-(SCH3)C = C(S)Ph]4 with pentacoordinated zinc, the corresponding compound of cadmium appears to have a polymeric structure. However, it forms a well-defined mu-S-bridged dimeric 1:1 adduct with dimethyl sulfoxide (DMSO), Cd[Ph(SCH3)C = C(S)-Ph]2(DMSO), of composition C32H32S5CdO, with hexacoordinated cadmium, crystallizing in the triclinic space group P1BAR with unit cell parameters a = 11.529 (4) angstrom, b = 12.955 (5) angstrom, c = 22.804 (8) angstrom, alpha = 106.480 (20)-degrees, beta = 92.590 (20)-degrees, and gamma = 94.680 (20)-degrees, with Z = 2. The coordination geometry of the cadmium ions is distorted octahedral, the DMSO is coordinated via oxygen, and the Cd-O bond length is 2.358 (6) angstrom. The sulfur ligands are bound in an anisobidentate fashion, with normal covalent Cd-S and Cd-mu-S bonds of 2.5072 (22) and 2.6364 (22) angstrom and elongated coordinative Cd-S bonds of 2.8045 (22) and 2.976 (3) angstrom, respectively. On reaction with 4-(dimethylamino)pyridine (dmapy), a hexacoordinated 1:2 adduct, Cd[Ph(CH3S)C = C(S)-Ph]2(dmapy)2, of composition C44H46N2S4Cd is formed, which crystallizes in the monoclinic space group C2/c with a = 17.483 (4) angstrom, b = 12.290 (3) angstrom, c = 19.963 (5) angstrom, beta = 98.998 (20)-degrees, and Z = 4. The mean covalent Cd-S and coordinate Cd-N bond distances of 2.556 (1) angstrom and 2.384 (4) angstrom are within normal ranges, and the mean coordinate Cd-S bonds of 2.869 (2) angstrom are elongated but genuine coordinate bonds. The coordination geometry of Cd is distorted octahedral, and the dmapy molecules are in cis positions opposing the coordinate Cd-S bonds. The adduct with 2,2'-bipyridyl (bpy), Cd[Ph(SCH3)C = C(S)Ph]2(bpy), of composition C40H34N2S4Cd, also contains hexacoordinated Cd and crystallizes in the triclinic space group P1BAR, with a = 13.652 (3) angstrom, b = 12.843 (7) angstrom, c = 10.5640 (20) angstrom, alpha = 101.39 (3)-degrees, beta = 94.200 (20)-degrees, gamma = 94.36 (3)-degrees, and Z = 2. The mean covalent and mean coordinate Cd-N bond lengths of 2.5260 (13) and 2.382 (36) angstrom are normal; the coordinate Cd-S bonds of 2.8151 (19) angstrom are elongated due to the anisobidentate attachment of the sulfur ligands. Cadmium ions thus have a greater tendency to adopt higher coordination numbers than zinc, which could account for some of the reactivity differences between the two elements in biological systems.