Synthesis and Characterization of Two Mononuclear MnIII Compounds with Mixed Schiff Base Ligands

Two mononuclear Mn compounds of Mn-III(salen)(L-1) and Mn-III(salen)(L-2) (H(2)salen = N,N'-ethylenebis-(salicylideneaminato), L-1 = 4-(2-hydroxybenzylideneamino)benzoic acid and L-2 = 4-(2-hydroxybenzylideneamino)-2-hydroxybenzoic acid) have been prepared and characterized by X-ray crystallography. Both compounds crystallize in the monoclinic system, space group P2(1)/c with a = 14.351(4), b = 14.955(3), c = 11.869(3) angstrom and beta= 91.529(3)degrees for 1; and those for 2: a = 14.439(9), b = 15.217(9), c = 11.660(7) angstrom and beta = 91.648(1)degrees. The compounds have similar structures, in which the Mn-III center adopts a distorted square-pyramidal geometry with the basal plane constructed by two N and two O atoms from the salen ligand and the apical position occupied by the carboxylate O atom from L-1 or L-2 ligand. The voltammetric behavior of the compounds is examined, which shows quasi-reversible one-electron reduction of Mn(III) to Mn(II). The reduction potentials of both compounds fall between -0.33 V [E-0(O-2/O-2 center dot(-))] and 0.65 V [E-0(O-1(2)/O-2 center dot(-))], which suggest that 1 and 2 could be potential mimics of Mn-SOD.