Oxygen out, sulfur in. The alkali metal sulfidotungstates K${}_2$[WS${}_4$] and novel Na${}_2$[WS${}_4$] ⋅ 4 H${}_2$O

An attempt to synthesize a holmium sulfidotungstate using potassium polysulfides as reactive flux resulted in orange single crystals of K${}_2$[WS${}_4$], isotypic to K${}_2$[MoS${}_4$] (orthorhombic; Pnma; a=935.10(3), b=694.22(2), c=1221.85(4) pm; Z=4). A similar attempt to obtain a neodymium sulfidotungstate with sodium polysulfide yielded a violet substance, which underwent hydrolysis yielding orange-yellow single crystals of Na${}_2$[WS${}_4$] ⋅ 4 H${}_2$O (monoclinic, C2/c, a=1098.08(4), b=904.46(3), c=1144.27(4) pm, β=101.577(3)°, Z=4). Further attempts to synthesize these products deliberately as single phase materials only proved to be successful for K${}_2$[WS${}_4$] but not for Na${}_2$[WS${}_4$] ⋅ 4 H${}_2$O. Both compounds contain non-condensed [WS${}_4$]${}^{2-}$ tetrahedra, which surround the alkali metal cations with coordination numbers of nine and eight in K${}_2$[WS${}_4$]. In Na${}_2$[WS${}_4$] ⋅ 4 H${}_2$O, the sodium cations are coordinated by two sulfide anions plus four water molecules, resulting in a coordination number of six. Besides crystal structure determination, infrared and single crystal Raman spectra were collected and the optical band gap of K${}_2$[WS${}_4$] was determined. (© 2022 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH)