Uranium(VI) complexes with a calix[4]arene-based 8-hydroxyquinoline ligand: Thermodynamic and structural characterization based on calorimetry, spectroscopy, and liquid-liquid extraction

Uranium(VI) complexes with a calix[4]arene-based 8-hydroxyquinoline ligand: Thermodynamic and structural characterization based on calorimetry, spectroscopy, and liquid-liquid extraction

Bauer, A.; Jäschke, A.; Schöne, S.; Barthen, R.; März, J.; Schmeide, K.; Patzschke, M.; Kersting, B.; Fahmy, K.; Oertel, J.; Brendler, V.; Stumpf, T.

The environmental aspects of ore processing and waste treatment call for an optimization of applied technologies. There, understanding of the structure and complexation mechanism on a molecular scale is indispensable. Here, the complexation of U(VI) with a calix4]arene-based 8-hydroxyquinoline ligand was investigated by applying a wide range of complementary methods. In solution, the formation of two complex species was proven with stability constants of log ß1:1 = 5.94±0.02 and log ß2:1 = 6.33±0.01, respectively. The formation of the 1:1 complex was found to be enthalpy driven (∆H1:1 = (– 71.5±10.0) kJ mol–1; T∆S1:1 = (–37.57±10.0) kJ mol–1), whereas the second complexation step was found to be endothermic and entropy driven (∆H2:1 = (32.8±4.0) kJ mol–1; T∆S2:1 = (68.97±4.0) kJ mol–1). Moreover, the molecular structure of [UO2(H6L)(NO3)-containing solution by the calix[4]arene-based ligand in solvent extractions.

Keywords: calixarene; liquid-liquid extraction; density functional theory; calorimetry; spectroscopic properties; chelate; uranium; X-ray crystal

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