The Novel Alkali Sulfidoferrates K9[FeIIIS4](S2) S, (K/Rb)6[Fe2IIIS6], Rb8[Fe4IIIS10], and K7[FeII/IIIS2]5

A series of new potassium and rubidium sulfido ferrates were synthesized from iron and sulfur using elemental potassium and Rb2S as alkali element sources. The structures of all title compounds were determined by means of single-crystal X-ray data. Isolated ortho anions [FeIIIS4]5, together with disulfide and sulfide anions, are the structure elements in K9[FeS4](S2)S (monoclinic, space group P21/c, a = 1068.58(2), b = 787.480(10), c = 2372.96(3) pm, = 102.9670(10)degrees, Z = 4, R1 = 0.0325). The diferrates A6[FeIII2S6], among which only the sodium and the cesium salts were known so far, contain dimers of two edge-sharing [FeS4] tetrahedra. The potassium and the monoclinic form of the rubidium compound (monoclinic, space group P21/c, a = 772.50(1)/796.06(5), b = 1251.24(2)/1291.35(8), c = 1002.80(1)/1032.40(6) pm, = 127.5260(10)/127.163(4), Z = 2, R1 = 0.0356/0.0466) crystallize with the Cs3GaSe3 structure type. The second, orthorhombic form of Rb6[FeIII2S6] is isotypic to the cesium ferrate (orthorhombic, space group Cmca, a = 1884.36(3), b = 695.660(10), c = 1296.09(2) pm, Z = 4, R1 = 0.0220) forming the Ba3AlSb3 structure type. The rubidium ferrate Rb8[Fe4S10] crystallizes with a new structure type (triclinic, space group P$\bar{1}$, a = 744.65(3), b = 851.21(3), c = 1042.77(4) pm, = 77.990(2), = 85.244(2) = 81.051(2)degrees, Z = 1, R1 = 0.0537). The structure exhibits novel tetrameres [Fe4S10]8 of edge-sharing tetrahedra, which represent segments of the well-known chain compounds A[FeS2]. K7[FeII/IIIS2]5 (monoclinic, space group C2/c, a = 2790.1(3), b = 1153.74(13), c = 720.17(8) pm, = 102.746(8)degrees, Z = 4, R1 = 0.0407) exhibits SiS2 analogous chains of edge-sharing [FeS4] tetrahedra and contains iron in oxidation states II and III in a 2:3 ratio. This compound is an interesting intermediate inbetween the ferrate(III) K[FeIIIS2] and K3[FeII/IIIS2]2, with a 1:1 ratio of FeII:FeIII.