X-Ray and electrochemical investigation on a series of cobalt(II) complexes with quinquedentate ligands and their reactivity towards dioxygen

Abstract

Cobalt(II) complexes with various derivatives of the linear quinquedentate ligand bis(salicylideneimine-3-propyl)amine have been prepared and their electrochemical behaviour and reactivity with dioxygen have been studied in dimethyl sulphoxide solution by cyclic voltammetry. A linear correlation was found between the cobalt(II)–cobalt(III) half-wave potentials (E_½) and the logarithms of the electrochemically determined equilibrium constants for the formation of the 1 : 1 dioxygen adducts. Steric and conformational effects are also discussed in the light of the structure of the oxygen active form of the bis(salicylideneimine-3-propyl)methylamine derivative which has been determined from three-dimensional X-ray diffractomer data. Crystals of the compound are monoclinic, space group P2₁/a, with a= 13.275(3), b= 16.476(4), c= 11.483(3)Å, β= 94.71(4)°, and Z= 4. The structure has been refined by least-squares techniques to R= 0.108 for 1 366 unique reflections with I > 3σ(I). The co-ordination geometry around the cobalt atom can be described in terms of a distorted trigonal bipyramid formed by the three nitrogen and the two oxygen atoms of the ligand molecule.