Electron spin resonance study of the species formed by reduction of iron(III) chelates of tetrasodium 3,10,17,24-tetrasulphonatophthalocyanine in aqueous solution

Abstract

Electron spin resonance measurements show that the deep blue iron(III) chelate of 3,10,17,24-tetrasulphonatophthalocyanine (tspc) exists as a low-spin iron(III) species in aqueous solutions of low pH and containing 20% v/v of dimethylformamide (dmf). Reduction of iron(III) tspc with sodium tetrahydroborate in aqueous solution leads to the formation of the e.s.r.-detectable violet coloured iron(I) tspc whose chemical stability at room temperature is increased in aqueous solutions containing 20% v/v dmf. Reduction of iron tspc with Na[BH₄] in aqueous solutions containing pyridine leads to the formation of a violet coloured species which does not exhibit an e.s.r. spectrum and is thought to be an iron(I) radical anion tspc chelate. This species is oxidised cleanly to iron(III) tspc by molecular oxygen. Reaction of iron(III) tspc with hydroxylamine under carefully controlled conditions of pH leads to the formation of a nitrosyl complex of the iron tspc chelate.