AN NMR STUDY OF IONIC SOLVATION OF ALKALINE EARTH CATIONS WITH DIMETHYLSULFOXIDE IN NITROMETHANE SOLUTION

A proton NMR method for the determination of the solvation numbers of alkaline earth cations with dimethylsulfoxide (DMSO) in nitromethane as diluent is described. The method is based on the monitoring of the resonance frequency of DMSO protons as a function of DMSO to metal ion mole ratio while keeping the metal ion concentration constant. The average solvation number of cations at any DMSO/metal ion mole ratio was calculated from the NMR chemical shift mole ratio data and was plotted against the mole ratio values. The solvation numbers of alkaline earth cations were extracted from the limiting values of the corresponding ii-mole ratio plots and were found to be 6 for Ba ,sr an d ca i ons and 5 for Mg ion . Effect of the presence of water on the solvation numbers of alkaline earth cations with DMSO was studied. In this case, the variation in the resonance frequency of H 0, brought about upon titration of the cations by DMSO, was also used to estimate the solvation number of cations with DMSO