REDOX CHEMISTRY OF MONONUCLEAR MANGANESE(II), BINUCLEAR MANGANESE(III) AND BINUCLEAR MIXED MANGANESE(II)-MANGANESE(III) COMPLEXES WITH 3-AMINOPYRAZINE-2-CARBOXYLATE IN DIMETHYLSULFOXIDE

Mn-II forms a yellow mononuclear species with the title ligand having a 1:2 stoichiometry and whose conditional stability constant is 8.9 x 10(10) M(-2). The c.v. of this complex shows an oxidation at +0.78 V versus s.c.e. Controlled-potential electrolysis at +0.80 V versus s.c.e. yields a binuclear species of Mn-III with a 1:2 metal:ligand stoichiometry. The addition of Mn-III(urea)(6)(ClO4)(3) to a solution of the ligand produces a mononuclear complex of Mn-III if the concentration of the metal ion is less than 1 mM. At higher concentrations a binuclear species is obtained. The tatter is reduced in two steps, at +0.24 and -0.58 V versus s.c.e. Controlled-potential electrolysis at 0.0 V produces a dark green complex after the transfer of 0.5 equivalents of charge per mole of Mn. This binuclear L(2)Mn(II)-Mn(III)L(2) mixed-valence complex can be obtained only by electrolysis of the binuclear L(2)Mn(III)-Mn(III)L(2) species. Attempts to prepare the complex chemically were unsuccessful - the binuclear Mn-III species was obtained in every case.