Electron spin resonance study of the species formed by reduction of manganese(II) chelates of tetrasodium 3,10,17,24-tetrasulphonato-phthalocyanine in aqueous solution

Abstract

E.s.r. spectroscopy has been used to identify the products formed by reduction of the low-spin manganese(II) chelates of tetrasodium 3,10,17,24-tetrasulphonatophthalocyanine Na₄(tspc) on addition of various reducing agents. Addition of hydrazine to an aqueous solution containing [Mn^II(tspc)]^4– leads to the formation of low-spin [Mn⁰(tspc)]^6– which is also formed on addition of sodium sulphide or dithionite to an aqueous solution of the manganese(II) chelate containing 10% v/v of pyridine. The addition of sodium tetrahydroborate to an aqueous solution of [Mn^II(tspc)]^4– is thought to lead to diamagnetic [Mn^I(tspc)]^5–. When pyridine or imidazole are present in an aqueous solution of [Mn^II(tspc)]^4–, the addition of Na[BH₄] leads to a free-radical species, which is thought to involve the phthalocyanine ring system. The magnetic parameters associated with the e.s.r. spectrum due to [Mn⁰(tspc)]^6– have been determined by computer simulation of the experimental spectrum. The values of these magnetic parameters, together with the absence of extra hyperfine interactions due to certain axial ligands, lead to the proposal of a 3d_xy ground-state configuration for the low-spin manganese(0) chelate.