On a Study of Spin-Lattice Relaxation Times of 19F, 31P, 1H, and 2H in Solutions of PF6− and PO3F2− in D2O and H2O

Abstract

The spin-lattice relaxation times of fluorine, phosphorus, protons, and deuterons in solutions of sodium hexafluorophosphate and sodium monofluorophosphate in water and deuterium oxide have been measured at 25 MHz by pulsed techniques over the temperature range 250–363°K. The fluorine and phosphorus spin-lattice relaxation times in both salt solutions have been found to be the sum of interactions due to spin-rotation and dipole-dipole contributions. The spin-rotation constants for fluorine and phosphorus in PF6− are 3.56 and 3.86 kHz, respectively. The spin-rotation constants for fluorine and phosphorus in PO3F2− are 23.6 and 21.4 kHz. Spin-rotation constants were also calculated from chemical shielding data. The results for the nearly spherical PF6− anion are in accord with rotation diffusion theory. The 31P relaxation data seem to indicate that the PF6− anion follows the J-diffusion model of McClung whereas the 19F relaxation data indicate that the M-diffusion model is followed. The reorientation correlation times of water and deuterium oxide molecules have also been determined for solutions containing PF6− and PO3F2− ions. These ions seem to affect the correlation times of the H2O and D2O molecules differently.