Oxygen−17 Nuclear Magnetic Resonance Study of the Hydration Shell of Nickelous Ion

Abstract

The solvation shell of nickelous ion in aqueous solution at room temperature was observed using 17O nuclear magnetic resonance. The hyperfine interaction A between the unpaired electrons of the nickelous ion and the 17O nucleus was found to be 3.0×107 cps. The relaxation time of the electron, assuming T1e=T2e, was found to be 4.3×10−12 sec. Calculations show that the relaxation of the 17O nucleus occurs through the scalar coupling with the unpaired electrons, whereas the relaxation of the protons occurs through the dipolar coupling. Consequently, in the latter case the calculated electron relaxation time is very sensitive to the Ni–H distance, whereas in the former it is independent of the Ni–O distance, but governed by the independently determined hyperfine coupling constant. It is also pointed out that in the expression for the dipoledipole interaction between the nuclei and the unpaired electrons it is necessary to distinguish between the longitudinal and transverse relaxation times of the electrons. The rate constant at 298°K for the exchange of water between the hydration shell and the bulk was found to be (3.0±0.3)×104 sec−1, and the enthalpy of activation 10.8±0.5 kcal/mole.