MONONUCLEAR MN(III) COMPLEXES WITH IMINE AMINE AND PHENOLATE COORDINATION

A new tetradentate schiff base ligand has been synthesized by condensation of di-isobutyraldehyde disulphide with 2-aminophenol. The ligand forms mononuclear Mn(III) complexes with imine and phenolate ligation, which are relatively rare. The ligand forms a mononuclear Mn(III) complex with the formula, [Mn(L)](acetate) when treated with Mn(acetate)3.2H2O under basic conditions. The resulting cationic complex can accept an anion like chloride, azide, or thiocyanate which replaces the acetate anion. Conductivity data in DMF solution indicate that the chloride and azide ions are strongly bonded to the metal to give neutral complexes while the thiocyanate and the acetate complexes behave as 1:1 electrolytes. Electronic absorption spectroscopic results are consistent with a five-coordinate square-pyramidal geometry for these complexes. In DMF, all the complexes exhibit quasi-reversible Mn(III)/Mn(II) couple where E1/2 values range between -0.77 and -0.89 V vs Ag/AgCl. The schiff base is reduced by NaBH4 to provide amine and phenolate coordination. The azide complex having the formula, [Mn(L')N3] has been synthesized to probe any possible shift in the Mn(III)/Mn(II) potential upon changing the two donor atoms from imine to amine. The E1/2 value for the square-pyramidal complex is found to be -0.78 V vs Ag/AgCl. Room temperature magnetic moment values for the complexes in the solid state lie in the range 4.90-5.10 B.M. (mu(eff)/mu(beta)) indicating high-spin Mn(III) complexes.