New Mononuclear Manganese(III) Complexes with Hexadentate (N4O2) Schiff Base Ligands: Synthesis, Crystal Structures, Electrochemistry, and Electron-Transfer Reactivity towards Hydroxylamine

Four new manganese(III) complexes of hexadentate Schiff base ligand obtained from N,N′-bis(3-aminopropyl)ethylenediamine and salicylaldehyde, or salicylaldehyde derivatives having N4O2 donor sets − [Mn(sal-N-1,5,8,12)]ClO4 (1), [Mn(5-Cl-sal-N-1,5,8,12)]ClO4 (2), [Mn(5-Br-sal-N-1,5,8,12)]ClO4 (3), and [Mn(3-methoxy-sal-N-1,5,8,12)]ClO4·H2O (4) − have been synthesized and characterized. The crystal structures of 1 and 4 have been determined, and the kinetics of the electron-transfer reactions between these complexes and hydroxylamine hydrochloride have been followed spectrophotometrically in the 5.5−8.0 pH range. Similar kinetic reactivities of all the complexes towards a particular species of the reductant were noted. Hydrogen-bonded adduct formation between the reactants prior to electron transfer seems to be a possible reaction pathway, according to analysis of the experimental data. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)