Tungsten-malate interaacation. Synthesis, spectroscopic and structural studies of homochiral S-malato tungstate (VI), A-Na_3[WO_2H(S-mal)_2]

摘要

Reaction of the sodium tungstate and malic acid at 1 to 2 ratio in weak acidic solution (pH 3.0-6.0) resulted in the first isolation and structural characterization of a tungsten(VI) malato complex A-Na3[WO2H(S-mal)2J (I) (malic acid = H3mal). The complex has been characterized by elemental analysis, UV and IR spcctroscopy. The IR spectra are consistent with an oxo-coordinated mononuclear structure as revealed by single crystal X-ray diffraction study. The tungsten atoms are quasi-octa- hedrally coordinated by two cis-oxo groups and two bidentate malate ligands via its alkoxy and (X-carboxyl groups, while the f3-carboxylic and carboxylate groups remain uncomplexed. The latter are bonded each other through strong hydrogen bonding, forming a catenarian chain, and the anions are connected in homochiral form. It is proposed that the chiral configuration of metal center in wild-type FeMo-co biosynthesis might be induced by the coordination of the chiral R-homocitric acid, while a mixture of raceme might be btained in the biosynthesis of Ni.fV-FeMv-cofactor.