Syntheses, crystal structures, and properties of new ternary chalcogenidesof group 4 metals: Rb4Ti3S14, Cs4Zr3S14, K4Hf3Se14, and K4ZrHf2Se14

The new ternary compounds Rb4Ti3S14, Cs4Zr3S14, K4Hf3Se14, and K4ZrHf2Se14 were prepared by reacting the respective transition metals in alkali metal polychalcogenide melts. Two crystallographically independent transition met al cations are present that are coordinated by eight chalcogen atoms (Q) in an irregular fashion or by seven chalcogen atoms yielding a distorted pent agonal bipyramid. The M(1)Q(8) and M(2)Q(7) polyhedra are connected by shar ing common edges or trigonal faces leading to the formation of infinite lin ear one-dimensional anionic chains running parallel to the [101] direction. The chains are separated by alkali metal cations. The optical band gaps de termined are 1.59 eV for Rb4Ti3S14, 2.35 eV for Cs4Zr3S14, and 2.02 eV for K4Hf3Se14. In-situ X-ray powder diffractometry demonstrates that Rb4Ti3S14 decomposes at 430 degreesC into Rb2S5 and TiS. During the cooling cycle the re-formation of the polysulfide is observed. According to this result the polysulfide could be prepared using TiS instead of metallic Ti as well.