The compounds Cs6Ti6S27 and Cs4BaTi6Se27 have been synthesized by means of the reactive flux method. Cs6Ti6S27 and Cs4BaTi6Se27 crystallize in a new structure type in the trigonal space group C34-R3 with three formula units in cells with hexagonal axes at T = 153(2) K of a = 13.5203(8) Å, c = 19.784(1) Å and a = 13.804(2) Å, c = 20.850(2) Å, respectively. The compounds Rb5AgTi6Se27 and Cs5AgTi6Se27 have also been synthesized by the reactive flux method. Rb5AgTi6Se27 and Cs5AgTi6Se27 crystallize in the trigonal space group C3v4-P31c with two formula units in cells with hexagonal axes at T = 153(2) K of a= 13.266(1) Å, c = 13.908(2) Å and a = 13.5713(4) Å, c = 13.9367(6) Å, respectively. The polar structures are closely related and consist of similar infinite one-dimensional ∞1[Ti2(Q2)4(Q) 2-] (Q = S, Se) chains that run along  and are separated by cations. If these chains are considered to be cylinders, then these structures adopt hexagonal closest-packing along , a general feature of the packing for known A/group IV/Q compounds (A = alkali metal). These chains are built from seven-coordinate TiQ7 pentagonal bipyramids that are bonded together by edge- and face-sharing in turn. Four Q22- groups are in the translational unit of the chain. An unusual feature of the Ag chalcogenides is octahedral coordination about Ag.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry