Preparation and Spectroscopic Characterization of Two Manganese (II) semiquinone Complexes

摘要

The complexes [CTA][Mn(II)(SQ)_3] were isolated in the solid state and purified.SQ is the o-semiquinone of L-dopa or dopamine and CTA is the cetyltrimethylammonium cation.These complexes were characterized by Raman,infrared,EPR and themrogravimetry (TG) techniques.The EPR spectra of the solids presented an intense signal characteristic of the o-semiquinone radical anion with g=2.0062 and g=2.0063 for L-dopa and dopamine,respectively.Six characteristic lines around the organic radical signal confirm the presence of the Mn~(2+) ion.The most intense Raman bands were observed at v=1360 for dopamine and at 1356 cm~(-1) for L-dopa and assigned to a C-O stretching with major C_1-C_2 character.The absence of an intense Raman banda t ca.v=1480 cm~(-1),characterizes the ligands as an o-semiquinone radical anion.Broad bands in the v=400-750 cm~(-1) region can be assigned to deformations associated with the five-member ring chelate including the manganese ion,the oxygens,and the C_1-C_2 bonds.The more intense IR bands for the dopamine and the L-dopa-derived ligands at v=1233 and 1229 cm~(-1) are assigned to vCO.Mass loss mechanisms for the two complexes,based on the TG results,were proposed and confirm the formula proposed.