Novel bidentate oxovanadium(IV) glycolate, α-hydroxybutyrate and citrate with terpyridine and their conversions to nitrosyl products.

A series of monomeric α-hydroxycarboxylato oxovanadium(IV) complexes [VO(Hcit)(tpy)]·HO (1) (Hcit = citric acid, tpy = 2,2':6',2-terpyridine), [VO(glyc)(tpy)]·5.5HO (2) (Hglyc = glycolic acid) and [VO(α-hbut)(tpy)]·3HO (3) (α-Hhbut = α-hydroxybutyratic acid) have been obtained from the reactions of vanadyl sulfate with α-hydroxycarboxylates and terpyridine in acidic solutions. These complexes feature bidentate citrate, glycolate or α-hydroxybutyrate respectively. The ligand chelates to vanadium atom through α-hydroxy (in 1) or α-alkoxy (in 2 and 3) and α-carboxy groups, while β-carboxy groups of citrate in 1 are free to participate strong hydrogen bonds with neighboring citrate. With comparable chelation, 1 shares a similar V-O distance [2.168(1) Å] with that observed in FeV-cofactor [2.17 Å] [1]. Moreover, nitrosyl vanadium complexes [V(NO)(glyc)(tpy)]·3HO (4) and [V(NO)(α-hbut)(tpy)]·4HO (5) were obtained via reductions of synthetic solutions of 2 and 3 with hydroxylamine respectively. The terminal oxygen atoms were substituted by linear nitrosyl groups in 4 and 5. They were fully characterized by UV-vis, IR, EPR spectra, X-ray structural analyses and theoretical bond valence calculations.