Ta5+ Displacements in CsTaQ3 (Q = S, Se, and Te): New One-Dimensional Materials with the BaVS3 Structure

The new compounds CsTaQ 3 (Q = S, Se, and Te) have been synthesized through stoichiometric reactions of the elements with Cs 2 Q n reactive fluxes at 923 K. Their crystal structures have been determined by single-crystal X-ray methods. CsTaQ 3 crystallize in the hexagonal space group − P 6 3 / mmc with two formula units per cell. Crystal data: CsTaS 3, a = 7.266(2) Å, c = 5.961(2) Å, V = 272.55(10) Å 3 ( T = 115 K), R w ( F 2 ) = 0.072 (NO = 114, NV = 11), R 1 = 0.034; CsTaSe 3, a = 7.500(1) Å, c = 6.182(1) Å, V = 301.15(7) Å 3 ( T = 115 K), R w ( F 2 ) = 0.106 (NO = 112, NV = 11), R 1 = 0.036; CsTaTe 3, a = 7.992(4) Å, c = 6.496(4) Å, V = 359.3(4) Å 3 ( T = 115 K), R w ( F 2 ) = 0.131 (NO = 111, NV = 10), R 1 = 0.038. The compounds adopt the BaVS 3 structure type and feature chains of face-sharing octahedra. The Ta 5+ centers are displaced from the centers of the Q 6 octahedra along the direction of the chains in a centrosymmetric fashion. Geometrical considerations and band structure calculations at the extended Hückel and density functional (DFT) levels of theory suggest that the most likely distortion pattern is the one with all Ta 5+ centers displaced in the same direction within a given chain. A second-order Jahn−Teller effect is responsible for this distortion. Very weak interchain communication would result in a centrosymmetric structure. The chains are separated by 12-coordinate Cs + cations. CsTaSe 3 is an insulator. CsTaTe 3 shows semiconducting behavior and is diamagnetic or weakly paramagnetic. Differential scanning calorimetry (DSC) and high-temperature powder diffraction data indicate that CsTaTe 3 undergoes a phase transition at ≈493 K.