An electron spin resonance study of dimer formation of copper(II) protoporphyrin IX

Abstract

From a study of the e.s.r. spectra of copper(II) protoporphyrin IX at suitable concentrations (1·0 × 10^–2M) in frozen solutions of dimethylformamide and trimethyl phosphate, a direct observation of the signal due to dimeric species formed in frozen solution has been made. Application of methods which involve computer simulation of the observed line shapes has enabled a determination of the Cu^II–Cu^II separation to be made. This distance has been found to be a little greater than that of closest approach found by X-ray methods in a related system. The increased distance is interpreted in terms of a solvation of the side groups attached to the macrocyclic system. The e.s.r. data have not provided evidence for dimerisation in copper(II) phthalocyanine-3,3,4″,4‴-tetrasulphonic acid in frozen aqueous solution.