Abstract
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 calix[4]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 ß(1:1)=5.94±0.02 and log ß(2:1)=6.33±0.01, respectively. The formation of the 1:1 complex was found to be enthalpy driven [ΔH(1:1)=(-71.5±10.0) kJ mol(-1); TΔS(1:1)=(-37.57±10.0) kJ mol(-1)], whereas the second complexation step was found to be endothermic and entropy driven [ΔH(2:1)=(32.8±4.0) kJ mol(-1); TΔS(2:1)=(68.97±4.0) kJ mol(-1)]. Moreover, the molecular structure of [UO(2)(H(6)L)(NO(3))](NO(3)) (1) was determined by single-crystal X-ray diffraction. Concluding, radiotoxic U(VI) was separated from a Eu(III)-containing solution by the calix[4]arene-based ligand in solvent extractions.