Binuclear manganese(III) complexes with carboxylate bridges: Synthesis, structure, electrochemistry and magnetic properties

A series of μ-oxo, μ-carboxylato binuclear manganese(III) complexes derived from bipy, phen and different carboxylate ligands have been prepared and characterized by IR and UV–vis spectroscopies, cyclic voltammetry, magnetic susceptibility and the X-ray crystallography. The electronic spectra of all the complexes show very similar features consisting of two absorptions in the visible region, one high intensity LMCT band and two intra-ligand transitions in the UV region. The cyclic voltammograms of the complexes exhibit four steps in most cases, each consisting of a one-electron transfer reaction. These probably correspond to Mn 2 III ↔ Mn IV Mn III ↔ Mn 2 IV oxidation and Mn 2 III ↔ Mn III Mn II ↔ Mn 2 II reduction processes. The structure of complex 2 has been determined by the X-ray crystallography and consists of a binuclear [Mn 2 (bipy) 2 (μ- O )(μ-OOCR) 2 (NO 3 )(H 2 O)] + cation (R = CH 2 Cl) with a ClO 4 - anion. Low temperature magnetic susceptibility measurements show that there is a weak ferromagnetic interaction in 1 (R = Ph) ( J  = +0.43 cm −1 ) and a weak antiferromagnetic interaction between the metal centers in 2 (R = CH 2 Cl) ( J  = −0.15 cm −1 ).