Infrared spectroscopic investigation of sorption of nitric oxide by β-metal phthalocyanines of the first transition period

Abstract

I.r. spectroscopic investigation of microcrystalline MPc films evaporated for 10 h in high vacuum on KBr have been used to study the spectra of the α- and β-form and the sorption of NO by β-MPcs. The bands in the 760–770 and 770–780 cm^–1 regions thought hitherto to be characteristic of the α- or β-form are present in the spectra of both forms. Apart from NiPc and CuPc, which do not interact with NO under the conditions used, three different types of interaction of NO with MPcs at temperatures between room temperature and 600 K can be distinguished. In either type of interaction penetration of NO into the MPc lattice occurs, indicated by severe alterations in specific parts of the i.r. spectra. In CoPc, NO is complexed reversibly by the central ion. In FePc, complexing is similar but about one order of magnitude faster and desorption at elevated temperatures is accompanied by oxidative destruction of the Pc system. In MnPc, the reaction is of comparable velocity as in FePc; however, owing to generation of Mn–oxy–Pc, NO is bound in a nitrito or nitrato structure. The complex is protected by this against oxidative destruction during catalytic decomposition of NO by the complex even at 500–650 K.