Species distribution and coordination of uranyl chloro complexes in acetonitrile

The complex formation of the uranyl ion, UO22+, with chloride ions in acetonitrile has been investigated by principal component analysis of UV-vis absorption and U L3–edge EXAFS spectra. As a function of increasing [Cl]/[UO22+] ratio the species [UO2(H2O)5]2+, [UO2Cl(H2O)2(MeCN)2]+, [UO2Cl2(H2O)(MeCN)2], [UO2Cl3(MeCN)2] and [UO2Cl4]2 have been observed. The determined distances in the first coordination sphere are: U-Oax = 1.77 Å, UOH2O = 2.43 Å, UNMeCN = 2.53 Å and UCl = 2.68 Å. From the intermediate solution with the [Cl]/[UO22+] ratio of 2 a crystalline precipitate has been obtained. The crystal structure of this compound, [(UO2)4(2-Cl)4(3-O)2(H2O)2(CH3CN)4]•(CH3CN), has been determined.