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

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.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1391672
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Thermodynamics; Journal Volume: 80; Journal Issue: C
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Yang, Yanqiu, Zhang, Zhicheng, Liu, Guokui, Luo, Shunzhong, and Rao, Linfeng. Effect of temperature on the complexation of NpO 2 + with benzoic acid: Spectrophotometric and calorimetric studies. United States: N. p., 2015. Web. doi:10.1016/j.jct.2014.08.022.
Yang, Yanqiu, Zhang, Zhicheng, Liu, Guokui, Luo, Shunzhong, & Rao, Linfeng. Effect of temperature on the complexation of NpO 2 + with benzoic acid: Spectrophotometric and calorimetric studies. United States. doi:10.1016/j.jct.2014.08.022.
Yang, Yanqiu, Zhang, Zhicheng, Liu, Guokui, Luo, Shunzhong, and Rao, Linfeng. Thu . "Effect of temperature on the complexation of NpO 2 + with benzoic acid: Spectrophotometric and calorimetric studies". United States. doi:10.1016/j.jct.2014.08.022.
@article{osti_1391672,
title = {Effect of temperature on the complexation of NpO 2 + with benzoic acid: Spectrophotometric and calorimetric studies},
author = {Yang, Yanqiu and Zhang, Zhicheng and Liu, Guokui and Luo, Shunzhong and Rao, Linfeng},
abstractNote = {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.},
doi = {10.1016/j.jct.2014.08.022},
journal = {Journal of Chemical Thermodynamics},
number = C,
volume = 80,
place = {United States},
year = {Thu Jan 01 00:00:00 EST 2015},
month = {Thu Jan 01 00:00:00 EST 2015}
}