Alkali Chalcogenido Dialuminates A ₆ [Al ₂ Q ₆ ] (

The alkali chalcogenido dialuminates A ₆ [Al ₂ Q ₆ ] ( A  = K, Rb, Cs; Q  = S, Se, Te), which form transparent clear crystals, were synthesized from melts of the pure elements. The crystal structures of all compounds were determined by means of X‐ray single crystal data. Invariably, they contain isolated dimers [Al ₂ Q ₆ ] ⁶⁻ of edge‐sharing [Al Q ₄ ] tetrahedra in different monoclinic crystal arrangements: K ₆ [Al ₂ S ₆ ] forms the K ₆ [Fe ₂ O ₆ ]‐type structure ( C 2/ m , a  = 838.64(2), b  = 1282.31(4), c  = 746.06(2) pm, β  = 102.1014(5)°, Z  = 2, R 1 = 0.0083). The rubidium sulfido as well as all selenido and tellurido aluminates crystallize in the Cs ₆ [Ga ₂ Se ₆ ]‐type ( P 2 ₁ / c , a  = 791.33(5), b  = 1282.27(8), c  = 1029.85(6) pm, β  = 127.1938(13)°, Z  = 2, R 1 = 0.0326 for Rb ₆ [Al ₂ S ₆ ]). Finally, the cesium sulfido aluminate Cs ₆ [Al ₂ S ₆ ] forms in a new structure type ( C 2/ c , a  = 1935.69(13), b  = 724.10(5), c  = 1339.49(9) pm, β  = 90.134(2)°, Z  = 4, R 1 = 0.0193), which is actually a t2 subgroup of the orthorhombic Ba ₆ [Al ₂ Sb ₆ ]‐aristotype. The bonding features within the dialuminate anion are explored using APW+lo DFT band structure as well as molecular DFT calculations. The calculated bandgaps of the three Rb salts are experimentally verified by means of UV/vis spectroscopy (DRS). The crystal chemistry of the overall nine (12, including the oxides) dialuminates is discussed—and compared with the corresponding gallates, indates and ferrates(III)—by means of a structure map and a group‐subgroup tree connecting all occurring structure types.