Tungsten–malate interaction. Synthesis, spectroscopic and structural studies of homochiral S-malato tungstate(VI), Λ-Na3[WO2H(S-mal)2]

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 Λ-Na3[WO2H(S-mal)2] (1) (malic acid=H3mal). The complex has been characterized by elemental analysis, UV and IR spectroscopy. 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-octahedrally coordinated by two cis-oxo groups and two bidentate malate ligands via its alkoxy and α-carboxyl groups, while the β-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 obtained in the biosynthesis of NifV–FeMo-cofactor.