New Layered Quaternary Tantalum Thiophosphates Containing Binuclear [Ta2S10] Units: Synthesis and Crystal Structures of the Two New Compounds K0.42TaPS5 and Rb0.42TaPS5

The reactions of Ta with an in situ formed polythiophosphate melt of A2S3 (A = K, Rb), P2S5, and S at 500 °C yield the two new quaternary tantalum thiophosphates A0.42(2)TaPS5 (A = K (I) and Rb (II)). The compounds are isostructural and crystallize in the orthorhombic space group Fddd with Z = 16. Compound I has lattice parameters a = 9.6983(6) Å, b = 14.373(2) Å, c = 21.642(2) Å, and compound II a = 9.878(2) Å, b = 14.288(2) Å, c = 21.687(2) Å. Each Ta atom is surrounded by six S atoms in an octahedral environment. Two [TaS6] octahedra share a common edge to form the dimeric [Ta2S10] unit. These units are linked by sharing common edges with four tetradentate [PS4] groups yielding a two‐dimensional layered structure. The connection scheme leads to the formation of one type of cavities within the layers which are occupied by the alkali metal cations. The layers are stacked onto each other in a ···ABAB··· fashion and channels run along [011], [0‐11], [01‐1], and [0‐1‐1] with approximate dimensions of 4.1 · 7.9Å. The electron transfer from the alkali metals to the host material yields a short Ta‐Ta distance within the [Ta2S10] units. The compounds were characterized by energy dispersive X‐ray analysis and infrared spectroscopy in the MIR region.