Electron spin resonance study of the copper(II) and cobalt(II) chelates of 2,3; 7,8; 12,13; 17,18-tetrakis-(9,10-dihydroanthracene-9,10-diyl)porphyrazine

Abstract

The X-band e.s.r. spectra due to the benzene soluble copper(II)(1a) chelate of 2,3; 7,8; 12,13; 17,18-tetrakis-(9,10-dihydroanthracene-9,10-diyl)porphyrazine and the corresponding cobalt(II) chelate (1b) in the absence and presence of axially coordinating heterocyclic bases have been recorded. Spin Hamiltonian parameters have been determined by computer simulation of the various e.s.r. spectra and, in the case of the copper(II) chelate, compared with those obtained from the copper(II) chelates of certain phthalocyanines. The e.s.r. spectral properties of the cobalt(II) chelate (1b) porphyrazine in benzene solution were found to be remarkably dependent on the water hydration which accompanies the chelate in its isolation, requiring drying of the solution by molecular sieves. Axial coordination of the cobalt(II) centre of the chelate by pyridine, tetrahydrofuran or thiophene results in a large shift in the g_⊥ region of the spectrum, observed in the absence of axial coordination, to higher fields while causing a dramatic fall in the numerical values of ^CoA_∥ and ^CoA_⊥. The e.s.r. spectra due to frozen benzene solutions of the cobalt chelate (1b) containing various amounts of N-methylimidazole show that axial coordination of the cobalt(II) chelate centre by one heterocyclic base occurs at low concentrations of N-methylimidazole. At higher concentrations, two modes of binding of the N-methylimidazole may be clearly discerned, one characterized by an e.s.r. spectral component typical of low spin cobalt(II)(g_∥ < g_⊥) and a very unusual spectrum where the g-values are ca. 1.98.