Effect of temperature on the complexation of NpO 2 + with benzoic acid: Spectrophotometric and calorimetric studies

Journal Article · Thu Jan 01 04:00:00 EST 2015 · Journal of Chemical Thermodynamics

DOI:https://doi.org/10.1016/j.jct.2014.08.022· OSTI ID:1391672

Yang, Yanqiu; Zhang, Zhicheng; Liu, Guokui; Luo, Shunzhong; Rao, Linfeng

The equilibrium constants of the 1:1 NpO2+/benzoate complex were determined by spectrophotometric titrations at variable temperatures (T = 283 to 343 K) and the ionic strength of 1.05 mol · kg-1. The enthalpy of complexation at T = 298 K was determined by microcalorimetric titrations. Similar to other monocarboxylates, benzoate forms a weak complex with NpO2+ and the complexation is strengthened as the temperature is increased. The complexation is endothermic and is entropy-driven. The enhancement of the complexation at elevated temperatures is primarily attributed to the increasingly larger entropy gain when the water molecules are released from the highly-ordered solvation spheres of NpO2+ and benzoate to the bulk solvent where the degree of disorder is higher at higher temperatures. The spectroscopic features of the Np(V)/benzoate system, including the effect of temperature on the absorption bands, are discussed in terms of ligand field splitting and a thermal expansion mechanism.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1391672
• Journal Information: Journal of Chemical Thermodynamics, Journal Name: Journal of Chemical Thermodynamics Journal Issue: C Vol. 80; ISSN 0021-9614
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY