High-field31P N.M.R. investigations of the chemical shielding and indirect dipolar coupling of polycrystalline fluorophosphates

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Abstract
31P chemical shielding and indirect dipolar coupling data of the polycrystalline fluorophosphates K2PO3F, Na2PO3F, BaPO3F and K2P2O5F2 were obtained from broad-line and magic angle sample spinning 31P N.M.R. measurements at 109·3 MHz. The N.M.R. spectra are interpreted in terms of the model established by Vander Hart and Gutowsky. For interpreting the spectrum of K2P2O5F2 the theory was extended to the case of nonaxial 31P chemical shielding tensors. The values of the 31P shielding anisotropy Δσ and the asymmetry parameter η of the fluorophosphates are explained on the basis of the assumption that in phosphates the character of the chemical bond between phosphorus and bridging oxygen atoms (P-OB bond) is very similar to that between phosphorus and fluorine atoms (P-F bond). In addition, the directions of the principal axes of the shielding tensors with respect to the coordinate system of the fluorophosphate ions are discussed. As a result, further support was obtained for the assumption of the similarity of P-OB and P-F bonds in phosphates.