Raman Spectroscopic Studies on Intermolecular Interactions Of β-diketones and Their Complexes with CO{sub}2 under Supercritical Conditions

摘要

We have examined the solute-solvent interactions by measuring Raman spectra of CO{sub}2 in neat supercritical CO{sub}2 (sc-CO{sub}2), and sc-CO{sub}2 containing 1,1,1,2,2,6,6,7,7,7-decafluoroheptane-3,5-dione (Hdfh) and uranyl dfh complex [UO{sub}2(dfh){sub}2dmso] (dfh = 1,1,1,2,2,6,6,7,7,7-decafluoro-heptane-3,5-dionate; dmso = dimethyl sulfoxide), which has high solubility in sc-CO{sub}2 (3.1×10{sup}(-1) mol dm{sup}(-3)) at 9 MPa and 40°C. Two Raman peaks of CO{sub}2 molecules at around 1388 cm{sup}(-1) (v{sub}u) and 1286 cm{sup}(-1) (v{sub}l) were measured in the pressure range of 9 to 25 MPa at 40°C (density; 0.47 < ρ(g·cm{sup}(-3)) < 0.88). It was found that the Raman bands (v{sub}l and v{sub}u) of sc-CO{sub}2 containing Hdfh are shifted to lower wavenumber compared with those of neat sc-CO{sub}2 and that such a red-shift is not observed in sc-CO{sub}2 containing UO{sub}2(dfh){sub}2dmso. These phenomena are consistent with those observed in sc-CO{sub}2 containing hexafluoroacetylacetone (Hhfacac) and UO{sub}2(hfacac){sub}2dmso (hfacac = hexafluoroacetylacetonate). From these results, it was suggested that the Lewis acid-Lewis base (LA-LB) interactions between carbonyl oxygens of β-diketones and CO{sub}2 carbon, and the hydrogen bonding between enolic OH protons of β-diketones and CO{sub}2 oxygens are formed in sc-CO{sub}2 containing free β-diketones.