Speciation and Stability of Dioxovanadium(V) Complexes with Diethylenetriaminepentaacetic Acid at Different Ionic Strengths

UV spectroscopic measurements have been used to determine the binding ability of diethylenetriaminepentaacetic acid (DTPA) ligand towards the VO_2^+ ion at different ionic strengths of sodium chloride (0.11–0.95 mol·dm −3 ) and at T = 298 K. Dissociation constants of DTPA have been gathered from the literature. Calculations allowed us to identify the formation of three species VO 2 H 3 L, VO 2 H 2 L − and VO 2 HL 2− in the pH range of about 1.00–2.50. All of these complexes were characterized in terms of their stability constants on the basis of two different thermodynamic models (extended Debye–Hückel type and specific ion interaction theory) for the investigation of the ionic strength dependence of the stability and dissociation constants. Comparison with literature data is also reported.