Effect of temperature on the complexation of NpO2+ with benzoic acid: Spectrophotometric and calorimetric studies |
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| Institution: | 1. Institute of Nuclear Physics and Chemistry, Chinese Academy of Engineering Physics, Mianyang, Sichuan 621900, China;2. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA;3. Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439, USA;1. Department of Chemistry, College of Science, North University of China, Taiyuan 030051, China;2. State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030051, China;1. Department of Rare Earth, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland;2. RER Consultants, Fuchsbauerweg 50, D-94036 Passau, Germany;1. Vocational School of Health Services, Bart?n University, Bart?n, Turkey;2. Department of Chemistry, Eski?ehir Osmangazi University, Eski?ehir, Turkey;3. Scientific and Technological Research Application Center, Sinop University, Sinop, Turkey |
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| Abstract: | 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. |
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| Keywords: | Complexation Temperature effect Enthalpy Entropy Neptunium Benzoic acid |
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