SYNTHESIS AND CHARACTERIZATION OF BIS(MU-OXO)DIMANGANESE(III,III), BIS(MU-OXO)DIMANGANESE(III,IV), AND BIS(MU-OXO)DIMANGANESE(IV,IV) COMPLEXES WITH LIGANDS RELATED TO N,N'-BIS(2-PYRIDYLMETHYL)-1,2-ETHANEDIAMINE (BISPICEN)

The syntheses and characterization of a series of binuclear bis(mu-oxo )dimanganese(III,III), -(III,IV), and -(IV,IV) complexes of the genera l type [(A)4Mn(O)]2(2+/3+/4+), where the symbol A4 represents the four nitrogen atoms from a tetradentate ligand, are described. The ligands (A)4 used are s(2-pyridylmethyl)-N,N'-dimethyl-1,2-ethanediamine (bis picMe2en) and lmethyl)-N,N'-dimethyl-(-)D-1,2-cyclohexanediamine (bisp icMe2-(-)chxn). The syntheses and properties of the (III,III), (III,IV ), and (IV,IV), complexes (where (III,III) represents dimanganese(III, III), etc.) of bispicMe2en are described, as are those of the (III,IV) and (IV,IV) complexes of bispicMe2(-)chxn. The (III,IV) complex [(bis picMe2en)Mn(O)]2(ClO4)3.H2O (1) crystallizes in the monoclinic space g roup P2(1)/c with 4 formula units in a cell of dimensions a = 19.839(4 ) angstrom, b = 12.468(3) angstrom, c = 19.878(3) angstrom, and beta = 120.657(10)-degrees. The structure refined to a final R-factor of 0.0 62 based on 2874 reflections. The isomer crystallized is the cis-alpha -species, in which the pyridine nitrogen atoms are trans. The Mn(1)-O bonds are approximately 0.06 angstrom longer than the Mn(2)-O bonds, a nd the geometry at Mn(1) is significantly axially elongated; hence, th e manganese atoms can be distinguished as Mn(1) being Mn(III) and Mn(2 ) being Mn(IV). The Mn...Mn separation in the dimer is 2.678(2) angstr om. The (III,III) complex [(bispicMe2en)Mn(O)]2(ClO4)2.5H2O (3) crysta llizes in space group Aba2 of the orthorhombic system with four dinucl ear formula units in a cell of dimensions a = 15.561(3) angstrom, b = 16.703(3) angstrom, and c = 16.430(3) angstrom. The structure has been refined to a final R-factor of 0.0564 based on 2548 observed independ ent reflections. The isomer is again the cis-alpha-species. There is a crystallographic 2-fold axis passing through the center of the dimer and relating one manganese(III) center to the other. As is expected fo r a d4 Mn(III) ion, the geometry at manganese is axially elongated, th e average Mn-N(axial) bond being approximately 0.12 angstrom longer th an the average of the equatorial Mn-N bonds. The Mn...Mn separation in the dimers of 2.699(2) angstrom is comparable to that in related syst ems. The (III,IV) complex (bispicMe2(-)chxn)MnO2Mn(bispicMe2(-)chxn)]( ClO4)3 (4) crystallizes in the orthorhombic space group P2(1)2(1)2(1) with four dinuclear formula units in a cell of dimensions a = 13.098(3 ) angstrom, b = 16.297(3) angstrom, and c = 23.273(4) angstrom. The st ructure has been refined to a final R-factor of 0.0620 based on 3057 o bserved independent reflections. The isomer is cis-alpha, with roughly isotropic geometry at Mn(2) and axial elongation at Mn(1). Thus atom Mn(1) is the localized d4 Mn(III) site and Mn(2) is the localized d3 M n(IV) center. The Mn...Mn separation in the dimer is 2.693(2) angstrom . The complexes exhibit antiferromagnetic interactions, the (III,III) complex 3 having 2J = -201 cm-1, the (IV,IV) complexes 2 and 5 2J valu es of -205 and -211 cm-1, respectively, and the (III,IV) complexes 1 a nd 4 2J values of -320 and -293 cm-1, respectively.