Electron-spin resonance studies of manganese(II) 4,4′,4,″4‴-tetrasulphophthalocyanine

Abstract

E.s.r. measurements on manganese 4,4′,4″,4‴-tetrasulphophthalocyanine, [Mn^II(tspc)], confirm earlier reports that in the solid state this complex is obtained as a manganese(II) chelate. Measurements on aqueous solutions containing [Mn^II(tspc)] show that disaggregation of the chelate occurs as a result of small additions (5–10% v/v) of polar organic solvents such as NN-dimethylformamide. In these circumstances the e.s.r. spectrum has been assigned to a mixture of low-spin forms of the manganese(II) chelate. The solute–solute interactions which occur as a result of the addition of [Ni^II(tspc)] or [Zn^II(tspc)] to aqueous solutions of [Mn^II(tspc)] are characterized by the appearance of e.s.r. signals at 77 K attributable to a high-spin form of the manganese(II) chelate. The presence of ligands such as cyanide, pyridine, or imidazole, which are capable of axial interactions with [Mn^II(tspc)] promotes autoxidation of the manganese chelate in aqueous solution. Measurements at room temperature and 133 K provide evidence for a change in the spin state of the metal ion in the chelates as a result of changes in the pH of the solutions.