The mixed ligand cobalt(III) compounds of β-diketonates and quadridentate dianion Schiff bases

Abstract

A structural study is reported of the mixed chelate compounds of cobalt(III) with the quadridentate dianion ligand NN′-ethylenebis (salicylideneiminate)(salen and some methyl substistuted analogues) and some potentially bidentate monoanion ligands: β-diketonates, salicylaldehyde, and ω-nitroacetopheone. Structures in soluton have been correlated with solid state structures, now known from recent three-dimemsioanl X-ray crystallographic studies. Roliance is largely on n.m.r(¹H and ¹⁹F) data, with some help from the i.r and visible and u.v electronic spectra. The compounds generally have a distored octahedral six-co-ordinate structure with a non-planar strained salen moiety. Evidence is reported for isomers of many of the compounds and their interconversion, giving equilibrium mixtures in solution. Their range of stability has been investigated, and it is shown that in donor solvents reaction occurs giving the species [Co(salen)(solvent)₂][β-diketonate] in which the quadridentate ligand its more stable, essentially planar structure. No evidence could be found for species in which the β-diketonate is bonded to the metal in an alternative mode through the methylene carbon atom.