Studies on Coordination of Sterically Hindered Nitrogenous Bases to Nitrosyl(protoporphyrin IX dimethyl esterato) iron(II) by Electronic Absorption Spectroscopy

Abstract

Electronic absorption spectra for nitrosyl(protoporphyrin IX dimethyl esterato)iron(J1) (Fe(ppixdme) (NO)) complexes with stericaly hindered nitrogenous bases (2-methylimidazole and 2, 4, 6-trimethylpyridine) have been measured both at room temperature and at liquid nitrogen temperature and compared with those for Fe(ppixdme) (NO) complexes with unhindered nitrogenous bases (imidazole and pyridine). The system containing Fe(ppixdme)(NO)and hindered nitrogenous base in acetone exhibited the electronic spectra identical with those of fivecoordinate Fe(ppixdme)(NO) complex at room temperature and with those of six-coordinate Fe(ppixdme)(NO) complex with an unhindered nitrogenous base at liquid nitrogen temperature. This indicates that the hindered nitrogenous bases can coordinate to the axial vacant position of Fe(ppixdme)(NO) not at room temperature but at liquid nitrogen temperature.