A UNIQUE COORDINATION MODE FOR CITRATE AND A TRANSITION-METAL - K-2[V(O)(2)(C6H6O7)](2)CENTER-DOT-4H(2)O

Investigation of the aqueous coordination chemistry for citrate and va nadium(V) resulted in the isolation and characterization of K-2[V(O)2( C6H6O7)](2) . 4H(2)O (1) Complex 1 represents the first model of the t ricarboxylic acid coordinated to the heteroatom found in the cofactor of nitrogenase and may be relevant to other physiological forms of met abolized vanadium(V). 1 was characterized by elemental analysis, IR, U V-vis, and V-51 NMR spectroscopy, and X-ray crystallography. Complex 1 crystallizes in the space group P2(1)/n (No. 14) with a 9.3205(8) Ang strom, b = 11.739(1) Angstrom, c = 11.913(1) Angstrom, beta = 111.65(1 )degrees, V = 1211.4(4) Angstrom(3), and Z = 4. Full-matrix least-squa res refinement resulted in residuals of R = 0.041 and R(w) = 0.049. Th e citrate ligand displays a unique bidentate coordination to the vanad ium via the bridging hydroxyl group and a unidentate carboxylate group . The structure is best described as a dimer of two five-coordinate va nadium centers doubly bridged by hydroxyl oxygen atoms.