The Novel Alkali Sulfidoferrates K 9 [Fe III S 4 ](S 2 )S, (K/Rb) 6 [Fe III 2 S 6 ], Rb 8 [Fe III 4 S 10 ], and K 7 [Fe II/III S 2 ] 5

A series of new potassium and rubidium sulfido ferrates were synthesized from iron and sulfur using elemental potassium and Rb 2 S as alkali element sources. The structures of all title compounds were determined by means of single‐crystal X‐ray data. Isolated ortho anions [Fe III S 4 ] 5– , together with disulfide and sulfide anions, are the structure elements in K 9 [FeS 4 ](S 2 )S (monoclinic, space group P 2 1 / c , a = 1068.58(2), b = 787.480(10), c = 2372.96(3) pm, β = 102.9670(10)°, Z = 4, R 1 = 0.0325). The diferrates A 6 [Fe III 2 S 6 ], among which only the sodium and the cesium salts were known so far, contain dimers of two edge‐sharing [FeS 4 ] tetrahedra. The potassium and the monoclinic form of the rubidium compound (monoclinic, space group P 2 1 / c , a = 772.50(1)/796.06(5), b = 1251.24(2)/1291.35(8), c = 1002.80(1)/1032.40(6) pm, β = 127.5260(10)/127.163(4), Z = 2, R 1 = 0.0356/0.0466) crystallize with the Cs 3 GaSe 3 structure type. The second, orthorhombic form of Rb 6 [Fe III 2 S 6 ] 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, R 1 = 0.0220) forming the Ba 3 AlSb 3 structure type. The rubidium ferrate Rb 8 [Fe 4 S 10 ] 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, α = 77.990(2), β = 85.244(2) γ = 81.051(2)°, Z = 1, R 1 = 0.0537). The structure exhibits novel tetrameres [Fe 4 S 10 ] 8– of edge‐sharing tetrahedra, which represent segments of the well‐known chain compounds A [FeS 2 ]. K 7 [Fe II/III S 2 ] 5 (monoclinic, space group C 2/ c , a = 2790.1(3), b = 1153.74(13), c = 720.17(8) pm, β = 102.746(8)°, Z = 4, R 1 = 0.0407) exhibits SiS 2 analogous chains of edge‐sharing [FeS 4 ] 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[Fe III S 2 ] and K 3 [Fe II/III S 2 ] 2 , with a 1:1 ratio of Fe II :Fe III .