Synthesis, Crystal Structure and 19F NMR Parameters Modelling of Catif6(H2o)2 Yielding to a Revision of the Bond-Valence Parameters for the Ti4+/F- Ion Pair - CEA - Commissariat à l’énergie atomique et aux énergies alternatives Access content directly
Journal Articles Journal of Solid State Chemistry Year : 2022

Synthesis, Crystal Structure and 19F NMR Parameters Modelling of Catif6(H2o)2 Yielding to a Revision of the Bond-Valence Parameters for the Ti4+/F- Ion Pair

Abstract

CaTiF6(H2O)2 was synthetized by a solvothermal method and was found to be isostructural to SrTiF6(2H2O). The structure, refined from Powder X-Ray Diffraction (PXRD) data, is built from the connectivity of dimers [Ca2F10(H2O)4] of square antiprisms (SAP) [CaF5(H2O)3] and TiF6 octahedra. To assign the six 19F resonances to the six fluorine crystallographic sites of same multiplicity, 19 F magnetic shielding tensors have been calculated using the GIPAW method. Unusually, the plot of the experimental 19F isotropic chemical shift (δiso) values, as a function of the calculated 19F isotropic shielding (ssiso) values, shows a much better alignment for the experimental than for the DFT-optimized structure. Whereas, the dynamics of the structural water molecules under experimental conditions are not captured by the optimized structure, the experimental averaged structure provides a good account of the experimental data and a reliable assignment of the 19F resonances to the F sites. Finally, the previously established bond-valence (BV) parameter Rij for the Ti4+/F- ion pair (1.76 Å) leads to overestimated BV sum values for Ti. This trend has been observed for almost all other fluorotitanates. We then undertook to refine its value, using the Ti-F bond lengths from 70 carefully selected structures containing 134 Ti sites forming TiF6 octahedra, and leading to Rij. = 1.706 Å.
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Dates and versions

cea-03830435 , version 1 (26-10-2022)

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Christophe Legein, Monique Body, Jérôme Lhoste, Wei Li, Thibault Charpentier, et al.. Synthesis, Crystal Structure and 19F NMR Parameters Modelling of Catif6(H2o)2 Yielding to a Revision of the Bond-Valence Parameters for the Ti4+/F- Ion Pair. Journal of Solid State Chemistry, 2022, 319, pp.123793. ⟨10.2139/ssrn.4253528⟩. ⟨cea-03830435⟩
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