Structural and Infrared Spectroscopic Studies of Some Adducts of Divalent Metal Dihalides (mx2, M = Zn, Cd; X = Ci, Br, I) with Variously Hindered Monodentate Nitrogen (pyridine) Base Ligands (L = Pyridine, 2-Methylpyridine, and Quinoline) of 1:2 Stoichiometry

Single crystal X-ray structure determinations are described for a number of adducts of 1:2 MX2:L stoichiometry, [M = divalent metal (Zn, Cd); X = halide (Cl, Br, I), L = (variously hindered) monodentate nitrogen (pyridine) base: py = pyridine, 2-mpy = 2-methylpyridine, quin = quinoline]: [(2-mpy)(2)ZnX2] (X = Cl, Br) (isotypic, triclinic P (1) over bar, a approximate to 7.9(6), b approximate to 8.7, c approximate to 11.4 angstrom, alpha approximate to 86, beta approximate to 79.3, gamma approximate to 67 degrees, Z = 2), [(2-mpy)(2)ZnI2], [(quin)(2)ZnX2] (X = Br) (isotypic with the previously determined chloride, X = Cl, triclinic, P (1) over bar, a approximate to 8.7, b approximate to 9.6, c approximate to 11.1 angstrom, alpha approximate to 81, beta approximate to 73, gamma approximate to 72 degrees, Z = 2); [(quin)(2)ZnI2]; [(2-mpy)(2)CdX2], X = Br {isotypic with [(2-mpy)2ZnX2], X = Cl, Br (above)}, X = I {isotypic with [(2-mpy)(2)ZnI2] (above)}; [(quin)(2)CdI2]. A single molecule, with a four-coordinate quasi-tetrahedral metal atom, N2MX2, comprises the asymmetric unit of the structure in each of these. A one-dimensional polymer is found for [(quin)(2)Cd(mu-Cl)(2)]((infinity vertical bar infinity)), similar to those recorded previously for CdX2:py (1:2) (X = Cl, Br, I), the cadmium atom here lying on a 2-axis in tetragonal space group P (4) over bar2(1)c, and the quin ligands coordinating trans in a six-coordinate array about the cadmium, with successive cadmium atoms being linked by pairs of bridging chlorines. Adducts of MX2:L (1:1) stoichiometry, defined for M = Cd: [(2,4,6-trimethylpyridine)Cd(mu-1)(2)]((infinity vertical bar infinity)), and [(quin)Cd(mu-Br)(2)]((infinity vertical bar infinity)), are both infinite one-dimensional polymers center dot center dot center dot(mu-X)(2)Cd(L)(mu-X)(2)Cd(L)center dot center dot center dot, with five-coordinate trigonal bipyramidal cadmium atoms, the nitrogen donors being equatorial in the coordination spheres. The far-IR spectra of [L2MX2] (L = py, 2-mpy, quin; M = Zn, Cd; X = Cl, Br, I) are assigned and discussed in relation to the structures of the complexes.