PYRIDINE-TYPE COMPLEXES OF TRANSITION-METAL HALIDES .9. PREPARATION AND CHARACTERIZATION OF 2,4-DIMETHYLPYRIDINE AND 3,4-DIMETHYLPYRIDINE COMPLEXES OF COBALT(II) BROMIDE - THE CRYSTAL-STRUCTURE OF DIBROMOBIS(2,4-DIMETHYLPYRIDINE)COBALT(II) AND BROMOTETRAKIS(3,4-DIMETHYLPYRIDINE)COBALT(II) BROMIDE

Dibromobis(2,4-dimethylpyridine)cobalt(II) (1) crystallizes in an orth orombic (pseudo-tetragonal) space group P2(1)2(1)2(1) and bromotetraki s(3,4-dimethylpyridine)cobalt(II) bromide (2) in a monoclinic space gr oup C2/c. Cell parameters are obtained from Guinier-Hagg powder data: a = 7.6742(8), b = 7.6742(8), c = 28.114(6) Angstrom and Z = 4 for 1, and a = 14.817(4), b = 13.290(5), c = 14.871(4) Angstrom, beta = 90.55 (3)degrees and Z = 4 for 2. In 1 the cobalt(II) ion is tetrahedrally c oordinated with an approximate C-2v symmetry, which is apparent from t he infrared spectrum. In 2 the cobalt(II) ion has a rarely observed fi ve coordination with square pyramidal geometry. The consequent spectra l symmetry is C-2v. The thermal decomposition pattern of samples is si mple: an one-step process for 1 (DTG maximum at 335 degrees C) and a t hree-step process for 2, where one, one and two ligand moles are succe ssively released (DTG maxima at 130, 193 and 360 degrees C).