In Search of Aluminum Hexathiohypodiphosphate: Synthesis and Structures of ht-AlPS4, lt-AlPS4, and Al4(P2S6)3

We report the high‐pressure synthesis and the structure of aluminum hexathiohypodiphosphate, Al4(P2S6)3, along with the redetermination of the structures of two modifications of AlPS4. Al4(P2S6)3 crystallizes in the monoclinic space group C2 with a = 17.584(3), b = 10.156(2), c = 6.698(1) Å, β = 106.93(1)° in a superstructure of the layered FePS3 structure type with tripled a axis. Hereby, Al3+ occupies 2/3 of the Fe2+ sites in an ordered fashion. The structure model obtained from single‐crystal X‐ray diffraction was corroborated by TEM‐PED. The low‐temperature modification of AlPS4 with platelet‐like morphology shows tetragonal symmetry [space group P$\bar{4}$2c, a = b = 5.6572(9), c = 9.220(2) Å]. The orthorhombic high‐temperature modification with fibrous needle‐like morphology of AlPS4 is isotpyic with BPS4 [space group I222, a = 5.660(2), b = 5.759(2), c = 9.189(2) Å].