SYNTHESIS AND ELECTROCHEMICAL PROPERTIES OF OXO-BRIDGED MANGANESE DIMERS INCORPORATING ALKALI AND ALKALINE-EARTH CATIONS

The dimer [(1)Mn-III](2)(mu-O) (3) was synthesized by oxygenation of t he mononuclear Mn(II) complex in CH3CN. The ligand used was 3,3'-17-cr own-6-SAL-3-CH3-OPHEN (1). Dimer 3 reacted with KPF6 and Ba(SO3CF3)(2) in DMF forming 3 2KPF(6) and 3 2Ba(SO3CF3)(2) and these were isolated and characterized by spectroscopic and electrochemical means. All of the dimers participated in a reversible two-electron transfer process that produced the corresponding Mn-II,Mn-II (mu-oxo) dimer. Inclusion of cations into the crown ether portions of the dimer caused that form al reduction potential of 3 to shift to more positive values: E degree s (3) = - 120 mV, CH2Cl2; E degrees (3 2KPF(6)) = 0 mV, CH3CN; E degre es (3 2Ba(SO3CF3)(2)) = 180 mV, CH3CN all versus SSCE. Results of UV-V is experiments suggested that the shift in formal reduction potential was caused primarily by an electrostatic effect and not a perturbation of the d orbitals on the Mn(III) centers.