SYNTHESIS AND CHARACTERIZATION OF NOVEL OXO-BRIDGED DINUCLEAR AND HYDROXO-BRIDGED TRINUCLEAR CHROMIUM(III) ASSEMBLIES

The structural and spectroscopic properties of a novel dinuclear chrom ium-oxo and a trinuclear chromium-hydroxo complex are reported. The di nuclear assembly, (2)(mu-O2CMe)(bpy)(2)(H2O)(2)]ClO4.bpy.[bpyH]-ClO4 ( 1), crystallizes in the monoclinic space group Cc with a=16.8259(8) An gstrom, b=21.9622(11) Angstrom, c=14.6056(8) Angstrom, beta=122.1830(1 0)degrees, V=4568.0(4) Angstrom(3), and Z=4. The structure was refined with 4378 observed reflections having F>2.0 sigma(F), giving final R factors of 0.0721 and 0.1305 for R and R-w2, respectively. the [Cr-2(m u-O)(2)(mu-O2CMe)](+) core is structurally akin to those of recently r eported isoelectronic [Mn-2(mu-O)(2)(mu-O2CMe)](3+) complexes. The tri nuclear assembly, -3(mu-OH)(2)(mu-O2CMe)(4)(O(2)Cme)(2)(bpy)(2)]ClO4 ( 2).5CHCl(3) crystallizes in the triclinic space group P (1) over bar w ith a=16.104(5) Angstrom, b=17.623(5) Angstrom, c=12.236(3) Angstrom, alpha=93.33(1)degrees, beta=92.81(1)degrees, gamma=64.84(1)degrees, V= 3136.68 Angstrom(3), and Z=2. The structure was refined with 6732 obse rved reflections having F>2.33 sigma(F), giving final R factors of 0.0 602 and 0.0616 for R and R-2, respectively. Results of electronic, H-1 and H-2 NMR, and EPR spectroscopy, fast atom bombardment mass spectro metry, and variable-temperature magnetic susceptibility studies of the se materials and the use of Cr-oxo assemblies as isoelectronic models of the photosynthetic manganese assembly in high-S states are discusse d.