Département de chimie moléculaire

Two new terpyridine dimanganese oxo complexes [Mn2III,IV($μ$-O)2(terpy)2(CF3CO2)2]+ (3) and [Mn2III,III($μ$-O)(terpy)2(CF3CO2)4] (4) (terpy = 2,2':6,2''-terpyridine) were synthesized and their x-ray structures detd. In contrast to the corresponding mixed-valent aqua complex [MnIII2,IV($μ$-O)2(terpy)2(H2O)2]3+ (1), the two Mn atoms in 3 are not crystallog. equiv. The neutral binuclear monooxo Mn(III,III) complex 4 exhibits two crystallog. forms having cis and trans configurations. In the cis complex, the two CF3CO2- ligands on each Mn adopt a cis geometry to each other with one CF3CO2- is trans to the O of the oxo bridge. In the trans complex, the two coordinated CF3CO2- ligands have a trans geometry to each other and both are cis to the oxo bridge at each Mn. The electrochem. behavior of 3 in org. medium (MeCN) shows that this complex could be oxidized into its corresponding stable Mn(IV,IV) species while its reduced form Mn(III,III) is very unstable and leads by a disproportionation process to Mn(II) and Mn(IV) complexes. Complex 4 is only stable in the solid state, and it disproportionates spontaneously in MeCN soln. into the mixed-valent complex 3 and mononuclear [MnII(terpy)2]2+ (2), thereby preventing the observation of its electrochem. behavior. [on SciFinder(R)]