A NOVEL TRIPLY BRIDGED DINUCLEAR MANGANESE(III) COMPLEX CONTAINING THE [MN2O(OAC)(2)](2+) CORE - SYNTHESIS, CRYSTAL-STRUCTURE AND PROPERTIES OF [MN-2(MU-O)(MU-OAC)(2)(BPEA)(2)](CLO4)(2)

The reaction of Mn(O2CCH3)(3) . 2H(2)O with the ligand N,N-bis(2-pyridylmethyl)ethylamine (bpea) in a 1:1 ratio in methanol followed by the addition of NaClO4 afforded the title compound [Mn2O(O2CCH3)(2)(bpea)(2)](ClO4)(2) (1) in 75% yield. Compound 1 was characterized by using several physical methods including single-crystal X-ray diffractometry. Compound 1 . 0.5H(2)O crystallizes in the orthorhombic space group Pbca (No. 61) with a = 38.780(2), b = 22.058(4), c = 19.719(5) Angstrom, V = 16 868(8) Angstrom(3) and Z = 16. There are two independent equivalents of compound 1 in the crystallographic asymmetric unit and there is a single unique water molecule in the crystal lattice. Both manganese atoms in each of the independent dinuclear units are in the +3 oxidation state and they are bridged by one oxo ligand (O2-) and two acetate groups. Each manganese atom is also bound to one facially-coordinating tridentate bpea ligand, with the aliphatic nitrogen donor situated trans to an acetate oxygen atom. Deviations from idealized octahedral symmetry at each manganese center are consistent with expectations for a d(4) electronic configuration. Compound 1 has an average Mn...Mn separation of 3.11 Angstrom and an average Mn-(mu L-O)-Mn angle of 122.7 degrees. The electronic absorption spectrum of 1 in CH3CN is very similar to other compounds that contain the {Mn-2(mu-O)(mu-O2CCH3)(2)}(2+) core. A cyclic voltammogram of 1 in CH3CN exhibits an oxidation wave (III,III to III,IV) at +0.65 V and a reduction wave (III,III to III,II) at -0.39 V versus the ferrocene/ferrocenium (Fc/Fc(+)) couple. The IR spectrum of 1 reveals two strong bands at 1566 and 1432 cm(-1) corresponding to the bridging acetate groups present in the compound. The X-band electron paramagnetic resonance (EPR) spectrum of 1 in dry CH3CN at 77 and 4 K is featureless. Compound I disproportionates in an H2O/CH3CN solvent mixture to give the (III,IV) binuclear species [Mn2O2(O2CCH3)(bpea)(2)](2+), which displays a characteristic 16-line g=2 EPR signal.