THERMODYNAMICS OF COMPLEXATION OF THE URANYL(VI) ION WITH PHENYLACETATE - THE CRYSTAL-STRUCTURE OF NAUO2L3 (L = PHCH2CO2-)

The stability constant and the enthalpy and entropy changes of formation of the 1:1 complex of uranyl(VI) with phenylacetate were determined by potentiometric and calorimetric titrations in 1.0 mol dm-3 aqueous solution of NaClO4 at 25-degrees-C. The values obtained for the 1:1 complex agree with the general relationship holding for aliphatic monocarboxylato uranyl(VI) complexes. The structure of NaUO2L3 (L = PhCH2CO2-) was determined by X-ray crystallography and refined to R = 0.063 based on 3662 observed reflections. The compound is monoclinic, space group P2(1)/n, with a = 25.056(5), b = 19.210(5), c = 16.136(6) angstrom, and beta = 101.69(3)-degrees. There are three independent NaUO2L3 complex molecules in the asymmetric unit of the cell. The UO2L3- anions, where three bidentate ligands are equatorially bonded to the uranyl ion, are structurally similar and are held together by a network of close contacts with the neighbouring Na+ ions.