Thermodynamical and Structural Study of Protactinium(V) Oxalate Complexes in Solution

The complexation of protactinium(V) by oxalate was studied by X-ray absorption spectroscopy (XAS), density functional theory (DFT) calculations, capillary electrophoresis coupled with inductively coupled plasma mass spectrometry (C) and solvent extraction. XAS measurements showed unambiguously the presence of a short single oxo-bond, and the deduced structure agrees with theoretical calculations. CE-ICP-MS results indicated the formation of a highly charged anionic complex. The formation constants of PaO(C2O4)(+), PaO(C2O4)(2)(-), and PaO(C2O4)(3)(3-) were determined from solvent extraction data by using protactinium at tracer scale (C-pa < 10(-10) M). Complexation reactions of Pa(V) with oxalate were found to be exothermic with relatively high positive entropic variation.