Abstract
Abstract Stability constants (log b101) of Th4+, UO2 2+, NpO2 + and Am3+ with [NaP5W30O110]14- were determined by solvent extraction (m = 0.1M NaCl) and found to be 6.18±0.07, 3.80±0.06, 2.98±0.04, and 5.85±0.05, respectively. The order of stability constants: Th4+>Am3+>UO2 2+>NpO2 + is due to electrostatic repulsion between the actinyl oxygens and oxygens on the polyoxometalate surface. The order of stability constants for metal complexes with [P2W18O62]6- is Th4+>UO2 2+>Eu3+>NpO2 + because the steric repulsion between actinyl oxygens and oxygens on polyoxometalate are less important. Enthalpies of complexation were measured by calorimetric titration of Th4+, UO2 2+, Nd3+ with [NaP5W30O110]14- and [P2W18O62]6-. The results indicate that the conformation and charge distribution of the microscopic surface structures are important factors in the formation of pseudocolloids.
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