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The two isotypic rubidium chalcogenido diferrates Rb 12 [Fe 2  Q  6 ]( Q  2 ) 3  ( Q =S/Se), which both form needles with green-metallic lustre, were synthesized from Rb 2 S, elemental iron, rubidium and sulfur ( Q =S) or from the pure elements ( Q =Se) at maximum temperatures of 500–800°C. Their triclinic crystal structures were determined by means of X-ray single crystal data (space group  P 1̅,  a =863.960(10)/903.2(3),  b =942.790(10)/982.1(3),  c =1182.70(2)/1227.4(4) pm,  α =77.4740(10)/77.262(6),  β =71.5250(10)/71.462(6),  γ =63.7560(10)/63.462(5)°,  Z =1,  R 1=0.0308/0.0658 for  Q =S/Se). The structures contain isolated dinuclear anions [Fe III  2  Q  6 ] 6−  composed of two edge-sharing [Fe Q  4 ] tetrahedra ( d Fe   − Q   =223.4–232.3/236.2–244.8 pm), which are also found in the two polymorphs of the pure alkali diferrates Rb 6 [Fe 2  Q  6 ]. The diferrate ions are arranged in layers running in the  a / b  plane around  z =0. Inbetween (aroundz  ≈   1  2$z \approx {1 \over 2}$   ), two crystallographically different disulfide/diselenide ionsQ  2   2  −$Q_2^{2 - }$    ( d Q   − Q   =211.1–213.4/237.9–241.1 pm), which are arranged in slightly puckered 3 6  nets, are intercalated. The intra-anionic distances and angles, the Rb coordination numbers and the molar volumes of these two ‘double-salts’ are in accordance with their corresponding reference compounds, Rb 6 [Fe 2  Q  6 ] and Rb 2  Q  2 . In addition, the two polymorphs of Rb 6 [Fe 2 Se 6 ], which are both isotypic with the sulfido analogous (Cs 6 [Ga 2 Se 6 ]-type, monoclinic, space group  P 2 1  /c ,  a =827.84(5),  b =1329.51(7),  c =1074.10(6) pm,  β =127.130(5)°,  R 1=0.0443 and Ba 6 [Al 2 Sb 6 ]-type, orthorhombic, space group  Cmce ,  a =1963.70(3),  b =718.98(3),  c =1348.40(7) pm,  R 1=0.0264) were prepared and characterized to complete the series of alkali diferrates(III) with oxido, sulfido and selenido ligands. The electronic band structures of the three Rb salts Rb 6 [Fe 2  Q  6 ], which have been calculated within the GGA+ U  approach applying an AFM spin ordering in the dimers and appropriate Hubbard parameters, allow a comparison of the chemical bonding characteristics (e.g. covalency) and the magnetic properties (magnetic moments) within the series of chalcogenido ligands. An analysis of the spin densities enables a comparative consideration of the mechanisms crucial for the magnetic ordering in chalcogenido ferrates. Ultimately, the electronic structure of the new compound Rb 12 [Fe 2 S 6 ](S 2 ) 3  nicely compares with those of the S 2 -free reference compound Rb 6 [Fe 2 S 6 ].

Rubidium chalcogenido diferrates(III) containing dimers [Fe 2 Q 6 ] 6− of edge-sharing tetrahedra ( Q =O, S, Se)