Synthesis and Characterization of Manganese Complexes Containing a Synthetic Macrocyclic Ligand

A number of manganese(II) and -(III) complexes with the uncharged 14-membered macrocyclic ligand, meso-5,5,7,- 12,12,14-hexamethyl-1,4,8,11 -tetraazacyclotetradecane ([14]aneN₄) have been synthesized and fully characterized. The Mn(II) compounds are oxygen sensitive and are easily destroyed by exposure to pH extremes. The manganese(III) complexes appear to be air stable and less sensitive to pH effects than the Mn(II) derivatives. The solid-state esr spectra of the divalent complexes indicate that the metal ion is experiencing a relatively small tetragonal distortion. The observed tetragonal spitting parameter, D, is 0.1-0.2 cm^-1. Chemical and electrochemical investigations show that the Mn^III-[14]aneN₄ complexes are easier to reduce than a number of manganese(III)-porphyrin complexes. These complexes also display magnetic moments and electronic absorption bands consistent with high-spin, tetragonally distorted d⁴ systems.