Oxo-bridged trinuclear and tetranuclear manganese complexes supported with nitrogen donor ligands: syntheses, structures and properties

Abstract

In this work, we present the syntheses of two μ₃-oxo bridged mixed-valent trinuclear Mn^IIMn^III complexes (1 and 2) and a μ₄-oxo bridged tetranuclear Mn^II₄ complex (3). All the three manganese complexes have been characterized crystallographically and by using different analytical techniques. Both mixed-valent trinuclear complexes 1 and 2 exhibited Jahn–Teller distortion for the Mn(III) ion. Variable temperature magnetic susceptibility studies of all three complexes revealed antiferromagnetic coupling between the closely placed paramagnetic manganese ions mediated via a μ-oxo bridge. Cyclic voltammetry studies displayed both Mn(III)/Mn(II) and Mn(IV)/Mn(III) redox couples in 1 whereas only the Mn(III)/Mn(II) couple was observed for complexes 2 and 3. Importantly, complexes 2 and 3 were found to disproportionate H₂O₂, and the catalase activity has been related to their structural features and redox properties.