Thermodynamic, spectroscopic and DFT description of oxidovanadium(IV) complexes with malate and tartrate in aqueous solution

This investigation deals with coordination compounds of oxidovanadium(IV) with l-malic and l-tartaric acids in aqueous solution. The different binary systems are studied by potentiometric, spectroscopic techniques and DFT calculation in a wide concentration range and with different metal/ligand ratios. Electronic paramagnetic resonance spectroscopy (EPR) and molecular absorption spectrophotometry are employed. A speciation model is proposed for the metal/ligand systems elaborating the potentiometric data and the actuality of the model proposed was confirmed by the comparison of the speciation distribution with the nature and the intensity of EPR and UV–Vis spectra. This approach lead us to revise the speciation models previously proposed identifying the dinuclear species M2L2H−n as predominant, for both vanadyl–ligand systems, also in case of high ligand excess. For each system investigated the individual spectrum of the relevant species is estimated and a careful exam of electronic spectra of vanadyl complexes provided some information about the structure-spectra relation.