Mononuclear manganese(III) complexes with imine/amine and phenolate coordination

Abstract

A new tetradentate Schiff base ligand (H2L) was synthesized by condensation of diisobutyraldehyde disulfide with 2-aminophenol and hydrogenated to form the satd. analog (H2L'). In MnLX (X = Cl, N3, NCS) and the ligands have imine and phenolate ligation, which are relatively rare. MnLOAc can accept an anion like chloride, azide, or thiocyanate which replaces the acetate anion. Cond. data in DMF soln. 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 5-coordinate square-pyramidal geometry for these complexes. In DMF, all the complexes exhibit quasireversible Mn(III)/Mn(II) couple where E½values 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, Mn(L')N3 was synthesized to probe any possible shift in the Mn(III)/Mn(II) potential upon changing the 2 donor atoms from imine to amine. The E½ value for the square-pyramidal complex is −0.78 V vs. Ag/AgCl. Room temp. magnetic moment values for the complexes in the solid state lie at 4.90-5.10 µB (µ eff/µ B) indicating high-spin Mn(III) complexes. on SciFinder(R).