| Abstract
| - The new compounds CsTaQ3 (Q = S, Se, and Te) havebeen synthesized through stoichiometric reactionsof the elements with Cs2Qn reactivefluxes at 923 K. Their crystal structures have been determined bysingle-crystalX-ray methods. CsTaQ3 crystallize in the hexagonalspace group−P63/mmcwith two formula units per cell.Crystal data: CsTaS3, a = 7.266(2)Å, c = 5.961(2) Å, V = 272.55(10)Å3 (T = 115 K),Rw(F2) = 0.072 (NO=114, NV = 11), R1 = 0.034;CsTaSe3, a = 7.500(1) Å, c= 6.182(1) Å, V = 301.15(7) Å3(T = 115 K),Rw(F2)=0.106 (NO = 112, NV = 11), R1 = 0.036;CsTaTe3, a = 7.992(4) Å, c= 6.496(4) Å, V = 359.3(4) Å3(T = 115K), Rw(F2) = 0.131(NO = 111, NV = 10), R1 = 0.038. Thecompounds adopt the BaVS3 structure type andfeaturechains of face-sharing octahedra. The Ta5+ centersare displaced from the centers of the Q6octahedra along the direction of the chains in a centrosymmetricfashion. Geometrical considerations and bandstructure calculations at the extended Hückel and densityfunctional (DFT) levels of theory suggest that the mostlikely distortion pattern is the one with all Ta5+centers displaced in the same direction within a given chain.Asecond-order Jahn−Teller effect is responsible for this distortion.Very weak interchain communication would resultin a centrosymmetric structure. The chains are separated by12-coordinate Cs+ cations. CsTaSe3 is aninsulator.CsTaTe3 shows semiconducting behavior and isdiamagnetic or weakly paramagnetic. Differential scanningcalorimetry(DSC) and high-temperature powder diffraction data indicate thatCsTaTe3 undergoes a phase transition at ≈493K.
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