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- Title
Thermodynamic and Structural Trends in Hexavalent Actinyl Cations: Complexation of Dipicolinic Acid with NpO<sub>2</sub><sup>2+</sup> and PuO<sub>2</sub><sup>2+</sup> in Comparison with UO<sub>2</sub><sup>2+</sup>.
- Authors
Xu, Chao; Tian, Guoxin; Teat, Simon J.; Liu, Guokui; Rao, Linfeng
- Abstract
The complexation of NpO22+ and PuO22+ with dipicolinic acid (DPA) has been investigated in 0.1 M NaClO4 by spectrophotometry, microcalorimetry, and single crystal diffractometry. Formation of 1:1 and 1:2 (metal/ligand molar ratio) complexes of DPA with NpO22+ and PuO22+ were identified and the thermodynamic parameters were determined and compared with those of UO22+. All three hexavalent actinyl cations form strong 1:1 DPA complexes with slightly decreasing but comparable stability constants from UO22+ to PuO22+, whereas the stability constants of the 1:2 complexes (log β2) decrease substantially along the series (16.3 for UO2L22−, 15.17 for NpO2L22−, and 14.17 for PuO2L22− at 25 °C). The enthalpies of complexation for the 1:2 complexes become less exothermic from UO2L22− (−28.9 kJ mol−1), through NpO2L22− (−27.2 kJ mol−1), and to PuO2L22− (−22.7 kJ mol−1). The trends in the thermodynamic parameters are discussed in terms of the effective charge of the cations and the steric constraints in the structures of the complexes. In addition, the features of the absorption spectra, including the wavelength and intensity of the absorption bands, are related to the perturbation of the ligand field and the symmetry of the actinyl complexes.
- Subjects
CATION analysis; SPECTROPHOTOMETRY; MICROCALORIMETRY; THERMODYNAMIC potentials; PERTURBATION theory; MATHEMATICAL symmetry
- Publication
Chemistry - A European Journal, 2013, Vol 19, Issue 49, p16690
- ISSN
0947-6539
- Publication type
Article
- DOI
10.1002/chem.201302119