Synthesis and Characterization of Three New Lithium‐Scandium Hexathiohypodiphosphates: Li4–3xScxP2S6 (x = 0.358), m‐LiScP2S6, and t‐LiScP2S6

We report the first examples of lithium rare earth metal hexathiohypodiphosphates(IV). Three new lithium‐scandium hexathiohypodiphosphates(IV) were synthesized and characterized. The compounds crystallize in three different structure types, featuring isolated ethane‐like [P 2 S 6 ] 4– hexathiohypodiphosphate(IV) units. Li 2.926 Sc 0.358 P 2 S 6 or Li 4–3 x Sc x P 2 S 6 ( x = 0.358) crystallizes in the space group P 3 1 m (no. 162) with a = b = 6.0966(5) Å, c = 6.5866(6) Å, V = 212.02(4) Å 3 , and Z = 1. The compound is isostructural to Li 2 FeP 2 S 6 as well as the Li ion conductor Li 4–2 x Mg x P 2 S 6 ( x = 1/3, 2/3). Monoclinic LiScP 2 S 6 was found to be a layered compound with van der Waals gaps. The layers consist of edge sharing octahedra that are occupied by Li, Sc, and P 2 in an alternating fashion. It is isostructural to LiAlP 2 S 6 and crystallizes in the space group C 2/ c (no. 15) with a = 6.933(1) Å, b = 10.754(2) Å, c = 11.694(2) Å, β = 94.41(3)°, V = 869.3(3) Å 3 , and Z = 4. Trigonal LiScP 2 S 6 crystallizes in the space group P 3 1 c (no. 163) with a = b = 6.363(1) Å, c = 12.386(3) Å, V = 434.3(2) Å 3 , and Z = 2, and is isostructural to AgInP 2 S 6 and AgScP 2 S 6 . Its structure is closely related to the monoclinic version, except that trigonal LiScP 2 S 6 features disordered [P 2/2 P 6/6 S 6 ] 4– units. The new phases were investigated by Raman spectroscopy, thermal analysis, and DFT calculations. We further demonstrate that Li 4–3 x Sc x P 2 S 6 shows significantly enhanced Li ion conductivity compared to the parent compound Li 4 P 2 S 6 .