A Structural and Electrochemical Investigation of 1-Alkyl-3-methylimidazolium Salts of the Nitratodioxouranate(VI)Anions[{UO_2(NO_3)_2}_2(mu-4-C_2O_4)]~2-,[UO_2(NO_3)_3]~-,and[UO_2(NO_3)_4]~2-

摘要

The properties of the 1-butyl-3-methylimidazolium salt of the dinuclear mu_4-(O,O,O',O'-ethane-1,2-dioato)bis[bis-(nitrato-O,O)dioxouranate(VI)]anion have been investigated using electrochemistry,single-crystal X-ray crystallography,and extended X-ray absorbance fine structure spectroscopy:the anion structures from these last two techniques are in excellent agreement with each other.Electrochemical reduction of the complex leads to the a two-electron metal-centered reduction of U(VI)to U(IV),and the production of UO_2,or a complex containing UO_2.Under normal conditions,this leads to the coating of the electrode with a passivating film.The presence of volatile organic compounds in the ionic liquids 1-alkyl-3-methylimidazolium nitrate(where the 1-alkyl chain was methyl,ethyl,propyl,butyl,pentyl,hexyl,dodecyl,hexadecyl,or octadecyl)during the oxidative dissolution of uranium(IV)oxide led to the formation of a yellow precipitate.To understand the effect of the cation upon the composition and structure of the precipitates,1-alkyl-3-methylimidazolium salts of a number of nitratodioxouranate(VI)complexes were synthesized and then analyzed using X-ray crystallography.It was demonstrated that the length of the 1-alkyl chain played an important rote,not only in the composition of the complex salt,but also in the synthesis of dinuclear anions containing the bridging mu_4-(O,O,O'O'-ethane-1,2-dioato),or oxalato,ligand,by protecting it from further oxidation.