Microcalorimetric titrations were performed to study interactions between actinide cations and weakly-binding ligands (e.g., nitrate) in aqueous solutions. The data were interpreted as the formation of weak inner-sphere Th(NO3)3+ complex in aqueous solutions at 25 �C and an ionic strength of 1 mol dm-3 (NaClO4). The nitrate anion probably coordinates with Th4+ in a bidentate mode, similar to that in the corresponding ThAc3+ complex. The complexation reaction is endothermic and entropy driven. As the small and positive enthalpy of complexation for ThNO3+ (5.2 kJ mol-1) suggests, the effect of temperature on the complexation of Th4+ with nitrate is slightly enhanced at higher temperatures.This work was supported by the Director, Office of Science, Office of Basic Energy Sciences of the U.S. DOE under Contract No. DE-AC02-05CH11231 at the Lawrence Berkeley National Laboratory.

Application of microcalorimetry for thermodynamic studies of weak actinide complexes

243rd National Meeting (2012)

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