DYNAMIC BEHAVIOR OF THE ION-PAIR (CH3)4P+/.ON(SO3)22- IN D2O SOLUTION BY H-1, C-13, AND P-31 NMR RELAXATION

We report an NMR investigation of the relative dynamics of the paramagnetic nitrosodisulfonate anion •ON(SO3)22- with respect to the tetramethylphosponium cation (CH3)4P+ in dilute D2O solutions at 25°C. The intermolecular longitudinal relaxation rates of the proton, carbon, and phosphorus nuclei on (CH3)4P+, due to their magnetic coupling with the •ON(SO3)22- electronic spins, have been measured for several ionic strengths. The theoretical relaxation rates are obtained by assuming that the ion-ion relative motion is described by solutions of the Smoluchowski equation including a force term that depends on the ion-ion potential of mean force calculated for a molecular solvent model. Two relaxation mechanisms of the nuclei due to the electronic spins are considered: the dipolar coupling and an additional effective hyperfine scalar interaction of the form (latin letter H with stroke sign)A(r)I·S. An experimental estimation of this hyperfine interaction is given from the paramagnetic contact shifts. The agreement between the theoretical and experimental relaxation rates is fair for the protons on (CH3)4P+ but only modest for the 13C and 31P nuclei. © 1990 American Chemical Society.