Synthesis and Characterization of the New Ternary Titanium Thiophosphate TiP₂S₇ and Comparison to Ti₄P₈S₂₉

The synthesis of the new thiophosphate TiP₂S₇ succeeded from TiS₂, P₄S₁₀, and elemental S in presence of Li₂S or elemental Cu and additional S. The crystal structure [orthorhombic, Pbcn, a = 23.9895(13), b = 6.8308(4), c = 19.6295(6) Å, V = 1905.0(2) ų, Z = 8, R₁ = 2.78 %, wR₂ = 6.35 % (all reflections)] consists of edge-connected TiS₆ octahedra and PS₄ tetrahedra, which form corrugated layers. Each of these layers interpenetrates a second one to form double layers parallel to the bc plane. The highly anisotropic characteristics are macroscopically observed by the easy cleavage property. One S atom coordinating the Ti atom is partially replaced by a S₂ dumbbell leading to a TiS₅(S₂) coordination. Including the dumbbell atoms the exact composition of the new compound is refined to TiP₂S_7.05. According to the crystal structure TiP₂S₇ shows two signals in ³¹P NMR spectra. Another known ternary thiophosphate with a very similar composition, Ti₄P₈S₂₉, was reinvestigated with special consideration of the S/S₂ occupational disorder, the composition was determined exactly to Ti₄P₈S_28.68 and found to be different from the previously reported.