Synthesis and characterization of some Mn(II) and Mn(III) complexes of N,N′-o-phenylenebis(salicylideneimine)(LH₂) and N,N′-o-phenylenebis(5-bromosalicylideneimine)(L′H₂). Crystal structures of [Mn(L)(H₂O)(ClO₄)], [Mn(L)(NCS)] and an infinite linear chain of [Mn(L)(OAc)]

A series of manganese(II) [Mn(L)] and manganese(III) [Mn(L)(X)] (X = ClO₄, OAc, NCS, N₃, Cl, Br and I) complexes have been synthesized from Schiff base ligands N,N′-o- phenylenebis(salicylideneimine)(LH₂) and N,N′-o-phenylenebis(5- bromosalicylideneimine)(L′H₂) obtained by condensation of salicylaldehyde or 5-Br salicylaldehyde with o-phenylene-diamine. The complexes have been characterized by the combination of IR, UV-Vis spectroscopy, magnetic measurements and electrochemical studies. Three manganese(III) complexes 3 [Mn(L)(ClO₄)(H₂O)], 5 [Mn(L)(OAc)] and 13 [Mn(L)(NCS)] have been characterized by X-ray crystallography. The X-ray structures show that the manganese(III) is hexa-coordinated in 3, it is penta-coordinated in 13, while in 5 there is an infinite chain where the MnL moieties are connected by acetate ions acting as bridging bidentate ligand. The cyclic voltammograms of all the manganese(III) complexes exhibit two reversible/quasi-reversible/ irreversible responses assignable to Mn(III)/Mn(II) and Mn(IV)/Mn(III) couples. It was observed that the ligand L′H₂ containing the 5-bromosal moiety always stabilizes the lower oxidation states compared to the corresponding unsubstituted LH₂. Cyclic voltammograms of the manganese(II) complexes (1 and 2) exhibit a quasi-reversible Mn(III)/Mn(II) couple at E_1/2 -0.08 V for 1 and 0.054 V for 2. © 2005 Elsevier B.V. All rights reserved.