FT‐IR Investigation of Rare‐Earth and Metal‐Ion Solvation. Part 14. Interaction between uranyl perchlorate and dimethyl sulfoxide in anhydrous acetonitrile

Abstract

AbstractThe interaction between the uranyl ion and perchlorate in anhydrous acetonitrile has been investigated by FT‐IR and Raman spectroscopy. Vibrations assigned to uncoordinated (u), monodentate (m), and bidentate (b) perchlorate anions were identified in 0.075M solutions. Quantitative data indicate that perchlorate is distributed as follows: 37 ± 2% are uncoordinated, 36 ± 7% are monodentate, and 27 ± 7% are bidentate. This is in agreement with the conductivity of the solutions which is at the lower end of the range accepted for 1:1 electrolytes. The splittings v4–v1(m) and v8–v1(b) of 147 and 246 cm−1, respectively, point to a large inner‐sphere interaction. An equilibrium occurs between two differently coordinated species. Various amounts of DMSO were added to 0.05M perchlorate solutions (R′ = [DMSO]t/[UO]t = 1–10). The v7 (SO) and v22 (CS) vibrations of DMSO were used to determine the average number of coordinated DMSO molecules per uranyl ion, which is close to 4. Some bidentate perchlorate ions are still present in these solutions, but all the MeCN molecules (2.6 on average) are expelled out of the inner coordination sphere. The data can again be interpreted in terms of an equilibrium between differently coordinated species. The average coordination number of the uranyl ion is 4.4, as the perchlorate salt in MeCN solution, and may be somewhat smaller in the presence of DMSO. The possible presence of dimeric species is also discussed.