In Search of Aluminum Hexathiohypodiphosphate: Synthesis and Structures of ht‐AlPS 4 , lt‐AlPS 4 , and Al 4 (P 2 S 6 ) 3

We report the high‐pressure synthesis and the structure of aluminum hexathiohypodiphosphate, Al 4 (P 2 S 6 ) 3 , along with the redetermination of the structures of two modifications of AlPS 4 . Al 4 (P 2 S 6 ) 3 crystallizes in the monoclinic space group C 2 with a = 17.584(3), b = 10.156(2), c = 6.698(1) Å, β = 106.93(1)° in a superstructure of the layered FePS 3 structure type with tripled a axis. Hereby, Al 3+ occupies 2/3 of the Fe 2+ 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 AlPS 4 with platelet‐like morphology shows tetragonal symmetry [space group P $\bar{4}$ 2 c , a = b = 5.6572(9), c = 9.220(2) Å]. The orthorhombic high‐temperature modification with fibrous needle‐like morphology of AlPS 4 is isotpyic with BPS 4 [space group I 222, a = 5.660(2), b = 5.759(2), c = 9.189(2) Å].