Oxygen out, sulfur in: The alkali metal sulfidotungstates K₂[WS₄] and novel Na₂[WS₄] ⋅ 4 H₂O

Abstract

Abstract 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, C 2/ 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.