Synthetic strategies, structures and properties of di and polynuclear cobalt complexes with H2salen type Schiff bases and their reduced analogues

A variety of polynuclear cobalt complexes with H2salen type Schiff bases and their reduced analogues have been synthesized and their structures and properties have been reported in literature. This review represents an overview on the synthetic strategies, structures, magnetic properties and biological activities of these complexes. It is worthy to mention here that only those complexes are considered in this review whose X-ray structures are available. The complexes may grossly be divided into three major sub classes; Cobalt(II), cobalt(III) and mixed valence cobalt(III)/cobalt(II) complexes. Different synthetic strategies have been applied for their preparation. In most of the cases, mixed valence complexes have been synthesized by the in situ partial (aerial) oxidation of cobalt(II) to cobalt(III). However, reduction of cobalt(III) precursors has also been identified as another synthetic route. Trinuclear cobalt(II)-cobalt(II)-cobalt(II) complexes were usually synthesised from cobalt(II) precursors in anaerobic condition. Different methods of synthesising di and polynuclear complexes are also discussed. The less explored areas of potential applications of these complexes are also discussed.