Ionic complexes from cobalt and zinc halides with pyridine N-oxide and trimethylamine oxide

Abstract

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⁺2l^–, [Co(Me₃NO)₄]²⁺2l^– 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.