title: Complexation of U(VI) with benzoic acid at variable temperatures (298-353 K): thermodynamics and crystal structures of U(VI)/benzoate complexes.
abstract: Thermodynamics of the U(VI) complexation with benzoic acid (HL) was studied by spectrophotometry at varied temperatures (298-353 K) with constant ionic strength (1.05 mol kg(-1) NaClO4). Two U(VI) benzoate complexes, UO2L(+) and UO2(OH)L(aq), were identified and their formation constants determined. The formation of both complexes is endothermic and driven exclusively by entropy. Two types of U(VI)/benzoate complex crystals were synthesized from aqueous solutions at different pH and ligand/metal ratios. Their structures were determined by single-crystal X-ray diffractometry. One structure is a 1 : 3 U(VI) benzoate complex (Na[UO2(C7H5O2)3]·2H2O), each benzoate holding a bidentate coordination mode to U(VI) in the equatorial plane of UO2(2+). The other is a U(VI) hydroxobenzoate complex with unique μ3-OH bridging ([(UO2)2(C7H5O2)2(μ3-OH)2]·4H2O). In the structure, each UO2(2+) ion holds five coordination oxygens in its equatorial plane, two carboxylate oxygens from two benzoate ligands and three oxygens from three μ3-OH groups.
authors.affiliation: Institute of Nuclear Physics and Chemistry, Chinese Academy of Engineering Physics, Mianyang, Sichuan 621900, China and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Yanqiu
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Teat
authors.affiliation: Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Zhicheng
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Institute of Nuclear Physics and Chemistry, Chinese Academy of Engineering Physics, Mianyang, Sichuan 621900, China.
authors.forename: Shunzhong
authors.initials: S
authors.lastname: Luo
authors.affiliation: Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Linfeng
authors.initials: L
authors.lastname: Rao