Carbonate complexes of vanadate

The interaction of vanadate with bicarbonate has been investigated using a combination of 51V NMR and potentiometric titrations. While such an interaction has long been suspected, little evidence and no information on the stability of the resulting complexes has previously been available. A global analysis of the results enabled the identification of two species, a mono-carbonato and a di-carbonato complex. The equilibrium constants of both species were determined between 1 and 56 °C, facilitating the calculation of the corresponding thermodynamic parameters.

51 V NMR spectra from the titration of vanadate with bicarbonate. Two key features to note are:(1) The broad, V1/HVO3CO22- peak at the down-field end of the spectrum. This peak becomes sharper and shifts upfield as more bicarbonate is added (towards the top of the figure).(2) The peak at approximately 585 ppm (indicated with an arrow) corresponding to a di-carbonatovandate complex. First visible in the 3rd spectrum, it increases in intensity as more bicarbonate is added.Figure optionsDownload as PowerPoint slide