Synthesis and characterization of novel oxo-bridged dinuclear and hydroxo-bridged trinuclear chromium(III) assemblies

The structural and spectroscopic properties of a novel dinuclear chromium-oxo and a trinuclear chromium-hydroxo complex are reported. The dinuclear assembly, [Cr-2(mu-O)(2)(mu-O2CMe)(bpy)(2)(H2O)(2)]ClO4.bpy.[bpyH]-ClO4 (1), crystallizes in the monoclinic space group Cc with a=16.8259(8) Angstrom, b=21.9622(11) Angstrom, c=14.6056(8) Angstrom, beta=122.1830(10)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(mu-O)(2)(mu-O2CMe)](+) core is structurally akin to those of recently reported isoelectronic [Mn-2(mu-O)(2)(mu-O2CMe)](3+) complexes. The trinuclear assembly, [Cr-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 with 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 observed reflections having F>2.33 sigma(F), giving final R factors of 0.0602 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 spectrometry, and variable-temperature magnetic susceptibility studies of these materials and the use of Cr-oxo assemblies as isoelectronic models of the photosynthetic manganese assembly in high-S states are discussed.