An Inorganic Double Helix Sheathing Alkali Metal Cations: ANb2P2S12 (A=K, Rb, 
Cs), A Series of Thiophosphates Close to the Metal-Nonmetal Boundary - 
Chalcogenide Analogues of Transition-Metal Phosphate Bronzes?

Gieck, Christine; Derstroff, Volkmar; Block, Thomas; Felser, Claudia; Regelsky, Guido; Jepsen, Ove; Ksenofontov, Vadim; Gütlich, Philipp; Eckert, Hellmut; Tremel, Wolfgang

doi:10.1002/chem.200103504

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An Inorganic Double Helix Sheathing Alkali Metal Cations: ANb₂P₂S₁₂ (A=K, Rb, Cs), A Series of Thiophosphates Close to the Metal-Nonmetal Boundary - Chalcogenide Analogues of Transition-Metal Phosphate Bronzes?

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Gieck, C., Derstroff, V., Block, T., Felser, C., Regelsky, G., Jepsen, O., et al. (2004). An Inorganic Double Helix Sheathing Alkali Metal Cations: ANb₂P₂S₁₂ (A=K, Rb, Cs), A Series of Thiophosphates Close to the Metal-Nonmetal Boundary - Chalcogenide Analogues of Transition-Metal Phosphate Bronzes? Chemistry - A European Journal, 10(2), 382-391. doi:10.1002/chem.200103504.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0018-60E4-A

Abstract

The new quaternary niobium thiophosphates ANb(2)P(2)S(12) (A = K, Rb, Cs) have been prepared and characterized. The title compounds were synthesized by reacting Nb metal, A(2)S, P2S5, and S at 600-700degreesC in evacuated silica tubes. They crystallize as "stuffed" variants of the tetragonal TaPS6 structure type in the tetragonal space group I (4) over bar 2d with eight formula units per unit cell and lattice constants a = 15.923(2) and c = 13.238(3) Angstrom for CsNb2P2S12, a = 15.887(3) and c = 13.132(3) Angstrom for RbNb2P2S12, and a = 15.850(2) and c = 13.119(3) Angstrom for KNb2P2S12. Their structures are based on double helices formed from interpenetrating, noninteracting spiral chains of binuclear [Nb2S12] cluster units and [PS4] thiophosphate groups. The cavities and tunnels, which are formed by the helical chains, are filled with A(+) ions. Temperature-dependent conductivity studies reveal thermally activated electrical transport behavior. This result is consistent with the observation of a temperature-dependent contribution to the P-31 MAS-NMR shift, suggesting that the delocalized s-electron spin density increases with increasing temperature. These findings are supported by the results of tight-binding band structure calculations which reveal that the unusual electrical transport behavior of ANb(2)P(2)S(12) is a consequence of the structure symmetry. Therefore, CsNb2P2S12 may be considered a chalcogenide analogue of metal phosphate bronzes.