¹⁷O NMR OF CRYSTALLINE SODIUM TRIMETAPHOSPHATE

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¹⁷O-enriched crystalline sodium trimetaphosphate was prepared by crystallisation of ¹⁷O-enriched sodium metaphosphate glass. ³¹P NMR spectra (MAS and Double- Quantum filtered MAS) are in good agreement with the crystal structure resolving two inequivalent phosphorus sites. ¹⁷O NMR static spectra enable to distinguish the bridging and non-bridging oxygens. Chemical shift, quadrupolar constants and asymmetry parameters are obtained by a fitting procedure. These NMR parameters for BO and NBO are in good accordance with those previously reported for sodium metaphosphate glass. The low resolution of the static spectrum does not enable to separate the crystallographic sites of oxygen and leads to an overestimated BO/NBO ratio. The POP bond angle within the P₃O₉^3- anion could be estimated and is in good accordance with the diffraction value.