Syntheses and spectroscopic and structural characterization of molybdenum(VI) citrato monomeric raceme and dimer, K-4[MoO3(cit)]center dot 2H(2)O and K-4[(MoO2)(2)O(Hcit)(2)]center dot 4H(2)O

摘要

Investigation of the aqueous coordination chemistry for citrate and molybdenum(VI) resulted in the isolation of molybdenum(VI) citrate monomeric raceme and dimer K-4[MoO3(cit)] . 2H(2)O (1) and K-4[(MoO2)(2)O(HCit)(2)] . 4H(2)O (2) (H(4)cit = citric acid). Complex 1 can serve as the first structurally characterized monomeric citrate molybdate and may represent an early mobilized precursor in the biosynthesis of FeMo-co (FeMo-cofactor). The two complexes have been characterized by elemental analyses and IR and NMR spectroscopies. The IR and NMR spectra are consistent with a monomeric species or a monooxo-bridged dinuclear structure, as revealed by a single crystal X-ray diffraction study. Compound 1 is monoclinic space group P2(1)/c with a = 7.225(1) Angstrom, b = 9.151(2) Angstrom, c = 22.727(2) Angstrom, beta = 94.93(1)degrees,V = 1497.1(7) Angstrom(3), and Z = 4. Full-matrix least,squares refinement resulted in residuals of R = 0.027 and R-w = 0.032. The molybdenum atom forms an octahedral coordination with three oxo groups and one tridentate citrate, in which the latter is coordinated through the alkoxy and vicinal carboxyl and much more weakly by one of the two terminal groups [2.411(3) Angstrom]. Compound 2 is triclinic space group P1 with 8.2728(8) Angstrom. b = 8.9514(8) Angstrom, c = 10.0605(9) Angstrom, alpha = 101.673(8)degrees, beta = 100.672(7)degrees, gamma = 112.938(7)degrees, V = 642.5(3) Angstrom(3), and Z = 1. Full-matrix least-squares refinement resulted in residuals of R = 0.033 and R-w = 0.039. The complex anion contains a linear (O2Mo)O(MoO2) core with the bridging oxo group lying at the center of inversion symmetry (Mo-O-b-Mo, 180 degrees). Each citrate ligand is three-coordinated to one molybdenum atom through the deprotonated hydroxy, alpha-carboxyl, and one beta-carboxyl group, making each metal atom six-coordinate. [References: 49]