ION-PAIRING AND MICROSCOPIC STRUCTURE OF R4NPF6 IN THE BINARY-SYSTEM CD3CN-CCL4 STUDIED BY NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

H-1 chemical shifts and spin-lattice relaxation times of R4NPF6 in CCl4-CD3CN have been measured in order to investigate the microscopic behaviour of the solute. Throughout the NMR measurements, the concentration of the solute was kept constant while the composition of the solvent was varied. The conductivity of the solution was also measured to establish whether the Fuoss association theory of ion pairing holds for this system. The relaxation time depends anomalously on the composition of the solvent, probably owing to preferential solvation. This point is discussed on the basis of a theory proposed by Covington and others together with a quasi-hydrodynamic theory for solution dynamics.