IONIC COMPLEXES FROM COBALT AND ZINC HALIDES WITH PYRIDINE N-OXIDE AND TRIMETHYLAMINE OXIDE

The range of ionic complexes obtainable from cobalt and zinc iodides with pyridine N-oxide (pyo) and trimethylamine oxide has been surveyed. The crystal structures of [Co(pyo)6]2+[CoCl4]2-, [Co(pyo)6]2+21-, [Co(Me3NO)4]2+2I- and [Zn(pyo)6]2+2[Zn(pyo)I3]- have been determined by X-ray analysis. There is an isomorphous series constituted by [Co(pyo)6]2+[CoX4]2- (X = Cl, Br or I) but the iodide decomposes to [Co(pyo)6]2+2I- in solution. Zinc gives four-co-ordinate molecular complexes [Zn(pyo)2X2] preferentially. With trimethylamine oxide the cobalt co-ordination is also limited to four, as in [Co(Me3NO)4]2+2I-. The steric restriction here is from CH3...O approaches. Spectroscopic evidence on [Co(Me3NO)3I]+I-, which is subject to ligand redistribution in solution, confirms its structure. Pyridine N-oxide differs from Me3NO in the preferential formation of a mixed-ligand anion, as in the isomorphous salts [NEt4]+-[Co(pyo)I3]- and [NEt4]+[Zn(pyo)I3] , and in [Zn(pyo)6]2+2[Zn(pyo)I3] . In the crystal of the last compound the polarity of the anions leads to their packing into double layers.