Two new terpyridine dimanganese complexes:: A manganese(III,III) complex with a single unsupported oxo bridge and a manganese(III,IV) complex with a dioxo bridge.: Synthesis, structure, and redox properties

Two new terpyridine dimanganese oxo complexes [Mn-2(III,IV)(mu-O)(2)(terpy)(2)(CF3CO2)(2)](+) (3) and [Mn-2(III,III)(mu-O)(terpy)(2)(CF3CO2)(4)] (4) (terpy = 2,2':6,2"-terpyridine) have been synthesized and their X-ray structures determined. In contrast to the corresponding mixed-valent aqua complex [Mn-2(III,IV)(mu-O)(2)(terpy)(2)(H2O)(2)](3+) (1), the two Mn atoms in 3 are not crystallographically equivalent. The neutral binuclear monooxo manganese(III,III) complex 4 exhibits two crystallographic forms having cis and trans configurations. In the cis complex, the two CF3CO2- ligands on each manganese adopt a cis geometry to each other; one CF3CO2- is trans to the oxygen of the oxo bridge while the second is cis. In the trans complex, the two coordinated CF3CO2- have a trans geometry to each other and are cis to the oxo bridge. The electrochemical behavior of 3 in organic medium (CH3CN) shows that this complex could be oxidized into its corresponding stable manganese(IV,IV) species while its reduced form manganese(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 CH3CN solution into the mixed-valent complex 3 and the mononuclear complex [Mn-II(terpy)(2)](2+) (2), thereby preventing the observation of its electrochemical behavior.