NMR RELAXATION STUDY OF NA2PFO3 IN SOLUTION - CHEMICAL-SHIFT ANISOTROPIES, BOND DISTANCES, J-COUPLING CONSTANTS, AND CORRELATION TIMES

The F-19 and P-31 NMR longitudinal relaxation times of the coupled two-spin system PFO3(2-) have been studied as a function of temperature. The phosphorus and fluorine isotropic chemical shifts, sigma-P(iso), and sigma-F(iso), change by 0.46 and 1.8 Hz/degrees-C, respectively. The phosphorus-fluorine spin-spin coupling constant, J(PF), changes by -2.0 Hz/degrees-C. The components of the chemical shift tensors are pH dependent, but, within experimental error, independent of temperature. At pH 8.0 and a temperature of 0-degrees-C, the values for the P-F internuclear distance (corrected for vibrational averaging), the phosphorus chemical shift anisotropy (CSA), and the fluorine CSA are 166.0 +/- 0.5 pm, -127.9 +/- 3.0 ppm, and +125.7 +/- 1.0 ppm, respectively. The value for J(PF) at a pH value of 8.0 or higher is -868.5 Hz; the absolute sign of J(PF) is negative. The CSA-dipolar interference effects due to multiple relaxation processes observed in coupled spin systems are suppressed in decoupled experiments. The values for the P-F bond distance obtained from both the coupled and decoupled solution-state NMR experiments (corrected for vibrational averaging), solid-state NMR experiments, and X-ray diffraction experiments are all in good agreement. For multiparameter NMR fitting processes, the accuracy of the results for simultaneously fit parameters is closely related to the absence of statistical correlation between the parameters fit. Data for the random field terms provide information about the motion of the solvent molecules hydrogen-bonded to the PFO3(2-) anions.