Effects of ring substituents on electrocatalytic activity of manganese phthalocyanines towards the reduction of molecular oxygen

Reduction of oxygen electrocatalyzed by adsorbed films of manganese phthalocyanine complexes is reported. The complexes studied were: manganese phthalocyanine (MnPc, 1); manganese tetraamino phthalocyanine (MnTAPc, 2); manganese tetrapentoxy pyrrole phthalocyanine (MnTPePyrPc, 3); manganese tetra phenoxy pyrrole phthalocyanine (MnTPPyrPc, 4); manganese tetra mercaptopyrimidine phthalocyanine (MnTMPyPc, 5) and manganese tetra ethoxy thiophene phthalocyanine (MnTETPc, 6). The reaction was conducted in buffer solutions of pH range 1–12. Rotating disk electrode voltammetry revealed two electron reduction in acidic and slightly alkaline media due to the formation of hydrogen peroxide. In highly basic media, water is the major product formed via four electron transfer. The reaction was found to be first order in the diffusing analyte oxygen

The synthesis and electrochemical behaviour of water soluble manganese phthalocyanines: Anion radical versus Mn(I) species

The following MnPc derivatives were synthesized: 1,(4)-tetra-(2-mercaptopyridine) phthalocyaninato manganese(III)(OH) (5a), quaternized 1,(4)-tetra-(2-mercaptopyridine) phthalocyaninato manganese(III)(OH) (5b), 2,(3)-tetra-(2-mercaptopyridine) phthalocyaninato manganese(III)(OH) (6a) and quaternized 2,(3)-tetra-(2-mercaptopyridine) phthalocyaninato manganese(III)(OH)(6b). Spectro-electrochemistry shows that the reduction of Mn(II)Pc to Mn(I)Pc occurs only when the complexes are in their quaternized form (5b and 6b). The reduction (to Mn(I)Pc(−2)) of the quaternized form occurs at a lower potential than that (to Mn(II)Pc(−3)) of the unquaternized form. This observation suggests that metal reduction (to Mn(I)Pc(−2)) versus ligand reduction (to Mn(II)Pc(−3)) in Mn(II)Pc complexes depends on the nature of the ring substituents

The synthesis and electrochemical behaviour of water soluble manganese phthalocyanines: Anion radical versus Mn(I) species

The following MnPc derivatives were synthesized: 1,(4)-tetra-(2-mercaptopyridine) phthalocyaninato manganese(III)(OH) (5a), quaternized 1,(4)-tetra-(2-mercaptopyridine) phthalocyaninato manganese(III)(OH) (5b), 2,(3)-tetra-(2-mercaptopyridine) phthalocyaninato manganese(III)(OH) (6a) and quaternized 2,(3)-tetra-(2-mercaptopyridine) phthalocyaninato manganese(III)(OH)(6b). Spectro-electrochemistry shows that the reduction of Mn(II)Pc to Mn(I)Pc occurs only when the complexes are in their quaternized form (5b and 6b). The reduction (to Mn(I)Pc(−2)) of the quaternized form occurs at a lower potential than that (to Mn(II)Pc(−3)) of the unquaternized form. This observation suggests that metal reduction (to Mn(I)Pc(−2)) versus ligand reduction (to Mn(II)Pc(−3)) in Mn(II)Pc complexes depends on the nature of the ring substituents