PYRIDINE-TYPE COMPLEXES OF TRANSITION-METAL HALIDES .6. PREPARATION AND CHARACTERIZATION OF 2.6-DIMETHYLPYRIDINE AND 3,5-DIMETHYLPYRIDINE COMPLEXES OF COBALT(II) HALIDES - THE CRYSTAL-STRUCTURE OF DI(2.6-DIMETHYLPYRIDINIUM)TETRACHLOROCOBALTATE(II) AND DICHLOROTETRAKIS(3,5-DIMETHYLPYRIDINE)COBALT(II)

(C7H10N)(2)[CoCl4] (1), Co(C7H9N)(4)Cl-2 (2), Co(C7H9N)(4)Br-2 (3) and Co(C7H9N)(4)I-2 (4) complexes have been studied by means of thermal analysis, IR and FIR spectroscopy, and X-ray crystallography. Crystal structures for compounds 1 and 2 have been determined. They crystallize in orthorhombic space groups with cell dimensions of a=16.744(3), b=8.832(2) and c=13.263(3) Angstrom; a=11.662(3), b=11.664(3) and c=10.608(3) Angstrom; space groups Pbcn and Pnnn; Z=4 and 2, and R-values 4.31 and 5.91% for 1256 and 931 observed reflections for 1 and 2, respectively. In 1 the structure consists of a tetrachlorocobaltate anion and a dimethylpyridinium cation connected by a weak N-H...Cl hydrogen bond with a N..Cl distance of 3.165(5) Angstrom. The chloride ions are tetrahedrally coordinated to the cobalt ion, with two pairs of symmetry related distances of 2.259(1) and 2.275(1) Angstrom. In 2 3,5-dimethylpyridine is coordinated to Co and the structure is pseudo-tetragonal. Four nitrogen atoms at distances of 2.186(4) Angstrom form the basal plane, and two chloride ions at the apexes with distances of 2.455(2) Angstrom complete the elongated octahedral coordination around Co. Cell dimensions for 3 and 4 determined by powder diffraction are a=b=11.863(1) and 12.1327(6) Angstrom; c=10.338(2) and 10.608(3) Angstrom, respectively. Co-Br and Co-I distances according to Rietveld refinement are 2.63 and 2.88 Angstrom, respectively. The structures have also been studied by FTIR. Vibrations in FIR spectra show the difference in coordination in structures 1 and 2. The thermal stability of the complexes in a nitrogen atmosphere has also been studied.