Synthesis, characterization, electrochemical and magnetic studies on manganese(III) complexes involving bridging carboxylates

A series of carboxylate-bridged manganese(III) complexes derived from Schiff bases obtained by the condensation of salicylaldehyde or 5-bromo-salicylaldehyde and different types of diamine have been synthesized and characterized and, in the case of [Mn2(L1)2(μ-ClCH2COO)](ClO4) (1), the structure has been obtained by X-ray crystallography. The structure of 1 consists of two manganese atoms separated by 5.487(3) Å and bridged by a carboxylate anion. This dinuclear structural unit is linked by bridging phenoxy oxygens to adjacent dinuclear units to produce a one-dimensional chain. Cyclic voltammograms of all the compounds exhibit grossly similar features consisting of a reversible or quasi-reversible MnIII/MnII reduction and a MnIII/MnIV oxidation. It has been observed that bromo-substitution stabilizes the lower oxidation state in the MnIII/MnII couple and destabilizes the higher oxidation state in the MnIII/MnIV couple. Variable temperature magnetic susceptibility measurements of 1 show a weak antiferromagnetic interaction. The magnetic behavior is satisfactorily modeled by inclusion of zero-field splitting and an intermolecular interaction component.