Département de chimie moléculaire

The electrochem. behavior of [MnIII(terpy)(N3)3] (1) (terpy = 2,2':6',2''-terpyridine), a structural model of the azide complex of the manganese superoxide dismutase (MnSOD), was studied in CH3CN soln. In CH3CN contg. either 0.1M Bu4NClO4 or tetraethylammonium trifluoroacetate (Et4NCF3CO2) as supporting electrolytes, the cyclic voltammogram of 1 exhibits one quasi-reversible redn. wave at E1/2 = -0.170 V vs. Ag|10 mM Ag+ and one quasi-reversible oxidn. wave at E1/2 = +0.675 V. These are both 1-electron waves, corresponding to the Mn(III)/Mn(II) and Mn(III)/Mn(IV) redox couples, resp. To evaluate the stability of the oxidized and reduced species of 1, exhaustive electrolyzes were carried out. Controlled-potential redns. at -0.35 V of solns. of 1 in CH3CN contg. 0.1M Bu4NClO4 or 0.1M Et4NCF3CO2 lead to the quant. conversion of 1 into the bridging N3- dimanganese(II) complex, [(N3)(terpy)MnII($μ$-N3)2MnII(terpy)(N3)]. This transformation is chem. reversible by an oxidn. process. Controlled-potential oxidn. at 0.8 V of a soln. of 1 in CH3CN+0.1M Bu4NClO4 produces a new mononuclear Mn(IV) complex characterized by ESR spectroscopy, which is stable only at or {\textless}-15°. If this oxidn. is conducted in CH3CN+0.1M Et4NCF3CO2, the stable dimanganese(IV) di-$μ$-oxo complex [(CF3CO2)(terpy)MnIV($μ$-O)2MnIV(terpy)(CF3CO2)]2+ is formed quant. owing to the presence of an excess of the coordinating CF3CO2- anions and residual H2O in the CH3CN soln. [on SciFinder(R)]