STERIC HINDRANCE IN 2,6-DISUBSTITUTED PYRIDINES .2. THE CRYSTAL-STRUCTURES OF TRANS-DICHLOROBIS(2,6-DIMETHYLPYRIDINE)NICKEL(II) AND TRANS-DICHLOROBIS(2,4,6-TRIMETHYLPYRIDINE)NICKEL(II)

trans-Dichlorobis(2,6-dimethylpyridine)nickel(II), [NiCl2(2,6-NC5H3(CH3)2] (1):M = 343.93, triclinic,P1BAR,a = 7.611(2), b = 8.060(2), c = 8.115(2) angstrom, alpha = 62.78(2), beta = 86.02(3), gamma = 114.02(3)-degrees, V = 383.8(2) angstrom3, Z = 1, D = 1.488 g cm-3, Mo K-alpha radiation, lambda = 0.71069 angstrom, mu = 16.08 cm-1, F(000) = 178, 296 K, R = 0.0328 for 2937 observed reflections with I > 3-sigma(I). trans-Dichlorobis(2,4,6-trimethylpyridine)nickel(II), [NiCl2(2,4,6-NC5H2(CH3)3)] (II): M = 371.98, monoclinic, P2(1)/c, a = 7.523(2), b = 14.614(3), c = 7.959(2), beta = 92.85(4)-degrees, V = 873.9(6) angstrom3, Z = 2, D = 1.413 g cm-3, Mo K-alpha radiation, lambda = 0.71069 angstrom, mu = 14.18 cm-1, F(000) = 388, 296 K, R = 0.0394 for 1652 observed reflections with I > 3-sigma(I). The nickel, chloride and nitrogen donor atoms are strictly planar due to the siting of the molecule on a center of symmetry. Ni-C] and Ni-N are 2.1940(8) and 1.935(1) angstrom for I and 2.1953(8) and 1.928(2) angstrom for II, respectively. The plane of the substituted pyridine ring in both cases is almost normal to the NiCl2N2 plane.