Synthese,structure cristalline et analyse vibrationnelle de l'hexathiohypodiphosphate de lithium Li4P2S6 |
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Authors: | R Mercier JP Malugani B Fahys J Douglande G Robert |
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Institution: | 1. Laboratoire d''Electrochimie des Solides, ERA 810, Université de Franche-Comté, 25030 Besancon Cedex, France;2. Laboratoire de Chimie Physique, Université de Franche-Comté, 25030 Besancon Cedex, France |
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Abstract: | The crystalline compound Li4P2S6 is obtained either by devitrification of Li4P2S7 glass at 450°C with sulfur formation or by crystallisation at 450°C of a Li2S, P and S melt. The structure determination has been solved by X-ray diffraction on a monocrystal. The unit cell is hexagonal with a = 6.070(4), c = 6.577(4) Å, V = 209 Å3, Z = 1. Intensities were collected at 293°K with Kα (λ = 0.71069 Å) Mo radiation on an automatic Nonius CAD-4 diffractometer. The structure was solved under the assumption of random disorder of P atoms over two sites (occupancy factor of 0.5). Anisotropic least-squares refinement with W = 1 gave R = 0.047 for 90 independent reflections and 9 variables. The structure is built according to an ABAB sequence sulfur packing. Per unit cell, four out of six octahedral sites are occupied by Li ions, and the other two are statistically filled (0.5) by PP pairs. The PP central bond (2.256(13) Å) links two staggered PS3 groups (PS = 2.032(5) Å) to form the D3d symmetry P2S4?6 anion. Infrared and Raman spectra show features very similar to those of Na4P2S6, 6H2O and MIIPS3 compounds. A new assignment in terms of symmetry species is proposed for the P2S6 internal modes, which is confirmed by a normal coordinate calculation using a valence force field; the stretching force constants fPP and fPS are equal to 1.6 and 2.7 mdyne Å?1, respectively. |
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