Physico-chemical study of copper(II) and cobalt(II) chelates of tetra-2,3-pyridinoporphyrazine

Abstract

The electronic and e.s.r. spectral data of the copper(II) and cobalt(II) chelates of tetra-2,3-pyridinoporphyrazine show that the electronic environment provided by the ligand is similar to that of the phthalocyanines. Potentiometric pH, spectrophotometric, and e.s.r. spectral measurements show that the water soluble NN′N″N‴-tetramethyl quaternized tetracationic forms of the copper(II) and cobalt(II) tetra-2,3-pyridinoporphyrazinates are free of solute-solute interactions, stable in a wide range of acidic solutions, but give rise to some decomposition in slightly alkaline solution. The cobalt(II) chelate forms five- and six-co-ordinate complexes with certain heterocyclic nitrogen ligands. The e.s.r. spectrum due to the imidazole complex of cobalt(II)NN′N″N‴-tetramethyltetra-2,3-pyridinoporphyrazinate indicates an unusual ground state of cobalt(II) in these circumstances. Spectrophotometric and e.s.r. spectral data indicate that the cobalt(II) chelate in aqueous solution undergoes a one-electron reduction of the metal centre as a result of reaction with ascorbic acid. The d.c. polarographic behaviour of the cobalt(II), nickel(II), and copper(II) chelates consists of waves with E_½ in the region of –0.55 and –1.20 V versus the saturated calomel electrode. The waves are polarographically irreversible but it has been shown that the first wave is due to a one-electron reduction of the chelates at the dropping mercury electrode.