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NMR STUDY OF BAFPO3: 31P AND 19F CHEMICAL-SHIFT ANISOTROPIES AND THE ABSOLUTE SIGN OF THE F-P COUPLING CONSTANT.
ILLINOIS UNIV URBANA NOYES CHEMICAL LAB
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The FPO3 ion in polycrystalline BaFPO3 was investigated from the point of view that it is a very slightly distorted, axially symmetric two-spin system. NMR line shape analysis for the 31P spectrum as a function of magnetic field yielded the following information 1 the chemical shift anisotropy is -145 plus or minus 20 ppm for phosphorus 2 the absolute sign of the F-P indirect dipolar coupling constant is negative 3 the internuclear F-P distance is 1.63 plus or minus 0.035A. Investigation of the 19F spectra was carried out through a second moment analysis as a function of magnetic field. It was found that the fluorine chemical-shift anisotropy is plus 182 plus or minus 22 ppm, where the sign is deduced from the sense of the line shape asymmetry. Furthermore, an estimate of the intermolecular dipolar contribution to the second moment was obtained by extrapolating the total second moment to low field and then subtracting the intermolecular dipolar contribution which is known from the 31P spectra. The intermolecular dipolar contribution is such that if BaFPO3 has a structure analogous to BaSO4, K2SO4, and K2FPO3, then there is a high degree of rotational disorder of the FPO3 ions in the crystal. Author
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