Is it possible to confirm that there are 2 or 3 cations (singly charged) as counter ions to doubly or triply charged anion single anions in an ionic liquid?
Ouh... Be careful, the analysis of self-diffusion coefficient by the Stokes-Einstein law is supposed to be done in a dilute solution. In ionic liquids, the diffusing species are also the solvent. Harris et al. have underlined that this approach is not correct (Harris KR. J Phys Chem B 2010;114:9572.). It was demonstrated for Nernst-Einstein law (relation conductivity -diffusion) but the assumptation that you will do in your case is the same... and so the consequence. I woudn't have confidence on the coordination number extracted from DOSY except if it is support to simulation...