Synthesis, crystal structure and optical properties of the new layered quaternary tantalum thiophosphate Rb 4Ta 4P 4S 24 based on the interconnection of Ta 2S 11 units by PS 4 tetrahedra
The new quaternary tantalum thiophosphate Rb 4Ta 4P 4S 24 was synthesized by reacting TaS 2 with a molten polythiophosphate flux formed by Rb 2S 3, P 2S 5 and S at 773 K. The compound crystallizes in the monoclinic space group P2 1/ n with a=13.849(3), b=17.647(4), c=15.900(3) Å, β=106.81(3)°, V=3720.1(13) Å 3 and Z=4. The structure is composed of dimeric [Ta 2S 11] units which are linked by [PS 4] tetrahedra to form 2∞[Ta 4P 4S 24] 4- layers. The significant structural difference of Rb 4Ta 4P 4S 24 to the known ternary and quaternary group 5 thiophosphates is the connection mode of the [M 2Q 11] units via [PS 4] tetrahedra. In the title compound the [Ta 2S 11] moieties are bridged by two tetradentate and two tridentate [PS 4] tetrahedra. Two types of cavities are observed in the 2∞[Ta 4P 4S 24] 4- layers with approximate diameters of 3.9·9.7 and 3.7·8.1 Å. The Rb + ions are located between the layers above and below the cavities. The compound was characterized with MIR, Raman spectroscopy and UV-vis diffuse reflectance spectroscopy.