Oxovanadium(IV) complexes of citric and tartaric acids in aqueous solution.

The complex-formation processes taking place in the systems containing VO(IV) and d-, l-, dl- or meso-tartaric acid or citric acid in aqueous solution were re-examined by combined use of pH potentiometry and spectroscopic (EPR and electronic absorption) methods. The results allowed a full characterization of the dinuclear species existing in the VO(IV)--d-, l- and dl-tartrate systems and indicated a different complexation behaviour in the corresponding meso-tartrate system. As its conformation is unfavourable for dimer formation, the meso ligand yields predominantly cyclic trinuclear species, one of them exhibiting distinctive EPR features. In the VO(IV)-citrate system, dinuclear species with structures different from those of the VO(IV) tartrates are suggested.