Hydrolysis and dimerization of Th4+ ion.
Hydrolysis of Th(4+) in aqueous solution was studied by density functional theory (DFT) calculations. First, stable coordination numbers (CNs) of Th(4+) hydrolysis products were studied systematically, and it was found that the CN significantly decreases as a stepwise hydrolysis reaction proceeds. The fourth hydrolysis product Th(OH)4(0) has CN6 with an octahedron coordination. Th(OH)4(OH2)2(0) can readily form a dimer complex Th 2(OH)8(0) via a Th-OH-Th bridging through an exergonic reaction with a Gibbs energy change of -24.0 kJ/mol. Consequently, dimerization inhibits Th(OH)4(0) to stay as stable aqueous species. The calculated result is in agreement with the fact that there is no direct evidence to confirm the presence of Th(OH)4(0) while oligomeric species such as Th 4(OH)16(0) are presumably present. Similar calculations on the Th(4+) disulfato complex reveal that the CN and the average Th-O distance of Th(SO4)2(0) remain almost the same as those in the Th(4+) aquo ion, which is also in agreement with experimental data.
Tsushima
Satoru
S
Institut für Radiochemie, Forschungszentrum Dresden-Rossendorf (FZD), Dresden, Germany. S.Tsushima@fzd.de