The effect of fast electronic relaxation times on the 1H and 7Li magnetic relaxation dispersion modulated by the translational encounter of cation/cation pairs

1H and 7Li magnetic relaxation dispersion data are presented, showing the field dependence of the spin–lattice relaxation rates of (H3C)4N+ and Li(H2O)n+ in Gd(III) and Mn(II) solutions. The limit of short electronic relaxation time is observed for Gd(III) up to about 7 T, in contrast to Mn(II) solutions wherein the intermolecular contribution to nuclear relaxation is dominated by relative translational diffusion. These results contradict the assumption made by Fries et al. (Chem. Phys. Lett. 286 (1998) 93) that the electron relaxation times may be neglected in the analysis of tetramethylammonium proton relaxation rates in Gd(III) solutions.