Effect of temperature on the complexation of NpO2+ with benzoic acid: Spectrophotometric and calorimetric studies. (January 2015)

• Record Type: Journal Article
• Authors: Yang, Yanqiu; Zhang, Zhicheng; Liu, Guokui; Luo, Shunzhong; Rao, Linfeng
• Is Part Of: Journal of chemical thermodynamics. Volume 80(2015:Jan.)
• Page Start: 73
• Page End: 78
• Publication Date: 2015-01
• Subjects: Complexation -- Temperature effect -- Enthalpy -- Entropy -- Neptunium -- Benzoic acid; Thermodynamics -- Periodicals; Thermochemistry -- Periodicals; Thermodynamique -- Périodiques; Thermochimie -- Périodiques; Thermochemistry; Thermodynamics; Periodicals; 541.369
• DOI: 10.1016/j.jct.2014.08.022
• Languages: English
• ISSNs: 0021-9614

Abstract

Graphical abstract: 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.