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

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 ${\mathrm{PF}}_6^{-}$ 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 ${\mathrm{PF}}_6^{-}$ anion are in accord with rotation diffusion theory. The ³¹P relaxation data seem to indicate that the ${\mathrm{PF}}_6^{-}$ 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 ${\mathrm{PF}}_6^{-}$ and PO₃F²⁻ ions. These ions seem to affect the correlation times of the H₂O and D₂O molecules differently.