Potassium Double Salts with the Mixed Trisulfidometalate Ions [MoOS3]2− and [WOS3]2−

In the course of the synthesis of mixed oxidosulfido molybdates and tungstates by passing H₂S gas through solutions of the oxido metalates, several new salts containing the metalates [MOS₃]²⁻ besides further anions (halides X⁻, hydrosulfide SH^– or thiosulfate S₂O₃^2–) were obtained as well-formed crystals. Their crystal structures have been determined using single crystal X-ray data. The salts containing SH^– as the additional anion crystallize with a new structure type (orthorhombic, space group Pmn2₁, M = Mo/W, T_M = 20/−125 °C: a = 957.7(2)/954.15(2), b = 636.2(2)/636.19(1), c = 812.4(2)/809.88(2) pm, Z = 2, R1 = 0.0319/0.0185). The mixed sulfidomolybdate/chloride K₃[MoO_1.25S_2.75]Cl (orthorhombic, space group Pca2₁, a = 1246.3(1), b = 623.20(4), c = 1230.44(8) pm, Z = 4, R1 = 0.0472) is isotypic with the sulfidotungstate K₃[WOS₃]Cl, but contains 25 % of the disulfido molybdate. The structures of the SH⁻ and the Cl⁻ salts are closely related: In both cases, the trisulfido metalates are overall coordinated by cuboctahedra of 12 K⁺ ions, and the small additional anions are centered in K⁺ octahedra. In this regard, the structures are both derivatives of the cubic perovskite (and thus the Cu₃Au) type. This crystallographic group-subgroup relation is discussed in detail. Yellow hexagonal columns of the double salt K₆[WOS₃]₂(S₂O₃) were obtained by the methanothermal decomposition of the disulfidotungstate K₂[WO₂S₂]. It crystallizes with a new structure type (hexagonal, space group P6₃mc, a = 983.78(8), c = 1227.3(1) pm, Z = 2, R1 = 0.0175). Like in the other mixed salts, the two crystallographically different [WOS₃]^2– anions exhibit an overall cuboctahedral coordination by 12 potassium cations. The smaller S₂O₃^2– anions are surrounded by nine K⁺ ions arranged in the form of two flat face-sharing octahedra. Again similar to the mixed halides and hydrosulfides, the two K polyhedra around the anions, here present in a 2:1 ratio, are arranged in a space-filling packing, in this case related to the ht-BaMnO₃ (and thus the Ni₃Ti) structure type. According to their 'double salt' character, the Mo/W−O and Mo/W−S distances and the intramolecular vibrational frequencies of the tetrahedral moieties of the title compounds are similar between them and those in the pure potassium trisulfido metalates. This further becomes apparent from the additive nature of their molar volumes, which correspond to the sum of the volumes of the simple salts KCl, KSH or K₂(S₂O₃) and K₂[MoOS₃].