High-field 31 P N.M.R. investigations of the chemical shielding and indirect dipolar coupling of polycrystalline fluorophosphates

Author: Haubenreisser Uwe   Sternberg Ulrich   Grimmer Arnd-Rüdiger  

Publisher: Taylor & Francis Ltd

ISSN: 1362-3028

Source: Molecular Physics, Vol.60, Iss.1, 1987-01, pp. : 151-163

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Abstract

31 P chemical shielding and indirect dipolar coupling data of the polycrystalline fluorophosphates K 2 PO 3 F, Na 2 PO 3 F, BaPO 3 F and K 2 P 2 O 5 F 2 were obtained from broad-line and magic angle sample spinning 31 P 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 K 2 P 2 O 5 F 2 the theory was extended to the case of nonaxial 31 P chemical shielding tensors. The values of the 31 P shielding anisotropy Δ&sgr; and the asymmetry parameter &eegr; 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-O B 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-O B and P-F bonds in phosphates.