On the detection by EXAFS spectroscopy of multimeric species and of complex anions in diethylether and diethylcarbonate

EXAFS spectroscopy has been shown to be a reliable tool for detecting the formation in solutions of molecular associations (LiBr)_n where n is solvent dependent. The signal Br^*...Br observed at 3.8₇ Å confirms the formation of tetrameric species (n=4) in diethylether (Et₂O) but only of dimers (n=2) in diethylcarbonate. Another signal observed at 2.4₅ Å has·been attributed to the pair Br^*...Li. The study of Li₂MBr₄–Et₂O solutions (M=Co, Cu, Zn) also affords new evidence for the formation of complex anions MBr₄^2– but the spectra obtained at the bromine or metalK-edges for LiZnBr₃–Et₂O solutions seems to indicate the formation of more complex aggregates (LiMBr₃)_q. While the signal of the shell Br^*...Br is found quite intense for the reference CBr₄–Et₂O system, it does not appear for the MBr₄^2– complex except for CuBr₄^2– where the Jahn-Teller effect might rigidify a distorted tetrahedral structure.Presented, in part, at the VIIth International Conference on Non-Aqueous Solutions, Regensburg, West Germany, Ausgust 1980.