Electrochemical synthesis and crystal structure studies of defective dicubane tetranuclear hydroxo and carboxamide ligand bridged cobalt(II)-cobalt(III) complexes with carboxamides produced from unprotected hydroxyaromatic carboxylic acids

Abstract

The benign synthesis of two new carboxamide ligands L 1 =1,2-bis(2-hydroxybenzamido)-4,5-dimethylbenzene (H4Me2hybeb) and L 2 =1,2-bis(2-hydroxy-3-naphthamido)-4,5-dimethylbenzene (H4Me2hyneb) from unprotected hydroxyaromatic carboxylic acids and the electrochemical synthesis of their mixed valance tetranuclear cobalt complexes, [Co4(μ3-OH)2(μ2-Me2hybeb)2(CH3CN)6] (1), and [Co4(μ3-OH)2(μ2-Me2hyneb)2(CH3CN)6] (2) by electrochemical oxidation of cobalt metal in acetonitrile solution is reported. The carboxamide ligands act as tetraanionic tetradentate ligands. The crystal structures of the two ligands L 1 and L 2 and of complex 1 have been determined in detail by X-ray crystallography. Complexes 1 and 2 consist of discrete mixed valence (Co2 II-Co2 III) defective dicubane molecular units, where each cobalt atom attains a distorted octahedral geometry. © 2014 Académie des sciences.