Spectrophotometric study on solubility of UO2(β-diketonato)2dmso complexes (β-diketonate=acetylacetonate, trifluoroacetylacetonate, hexafluoroacetylacetonate; dmso=dimethyl sulfoxide) in supercritical carbon dioxide

Abstract

Abstract We have investigated the molar extinction coefficients ( ɛ ) and solubility of UO 2 (β-diketonato) 2 dmso (β-diketonate = acetylacetonate (acac), trifluoroacetylacetonate (tfacac), and hexafluoroacetylacetonate (hfacac); dmso = dimethyl sulfoxide) in supercritical CO 2 (scCO 2 ) at 40 °C in the pressure range of 10–25 MPa (density; 0.6 ρ (g cm −3 ) ɛ values (M −1 cm −1 , M = mol dm −3 ) for UO 2 (acac) 2 dmso, UO 2 (tfacac) 2 dmso, and UO 2 (hfacac) 2 dmso in scCO 2 were estimated as 1.06 × 10 2 at 355 nm, 9.59 × 10 1 at 440.5 nm, and 7.95 at 486 nm, respectively, and were similar to that in C 6 H 14 . We also found out that the solubility of UO 2 (acac) 2 dmso, UO 2 (tfacac) 2 dmso, and UO 2 (hfacac) 2 dmso increases with increasing pressure and in order of UO 2 (acac) 2 dmso 2 (tfacac) 2 dmso 2 (hfacac) 2 dmso, i.e., 2.67 × 10 −3 −2 −1 M at 40 °C and 25 MPa. This is consistent with the order of an increase in the number of –CF 3 group in the coordinated β-diketonates. Furthermore, the equation proposed by Chrastil was found to hold for the solubility of UO 2 (β-diketonato) 2 dmso, that is, the logarithmic plot of solubility versus densities of scCO 2 showed the linear relationship. These phenomena suggest that the solubility of UO 2 (β-diketonato) 2 dmso is related with CO 2 solvation and the strength of interactions of CO 2 with the coordinated β-diketonates. In order to examine such interactions, we measured the dependence of 13 C chemical shifts of CO 2 in scCO 2 containing β-diketones on the density of scCO 2 . As a result, it was proposed that the solubility of UO 2 (β-diketonato) 2 dmso is mainly controlled by the van der Waals interactions between scCO 2 and particular sites (–CH 3 and –CF 3 groups) of ligands in UO 2 (β-diketonato) 2 dmso.