K 6 In 2 Q 6 ( Q = S, Se, Te): Missing Links in the Series of Alkali Chalcogenido Ditrielates(III)

The chalcogenido indates K 6 In 2 Q 6 ( Q = S, Se, Te) were synthesized from melts of the pure elements at a maximum temperature of 700 °C. All three potassium salts contain dinuclear units [In 2 Q 6 ] 6– of two edge‐sharing [In Q 4 ] tetrahedra. The sulfido and the selenido indate are isotypic and crystallize in the K 6 Mn 2 O 6 ‐type structure [monoclinic, space group P 2 1 / c, a = 784.32(9)/809.32(3), b = 1274.58(14)/1322.37(4), c = 836.48(9)/870.53(3) pm, β = 97.900(2)/97.5877(8)°, Z = 2, R 1 = 0.0123/0.0109; for Q = S/Se]. The tellurido indate K 6 In 2 Te 6 crystallizes in a new orthorhombic structure type [space group Pnma, a = 1793.70(12), b = 1491.55(11), c = 837.40(6) pm, Z = 4, R 1 = 0.0157]. In this structure, the telluride anions form a hexagonal close packing, in which K + cations occupy all octahedral voids; the In 3+ ions take 1/6 (but always adjacent) tetrahedral voids. This structure‐chemical relation to the h.c.p. packing, which is similarly found for most of the sodium dimetallates (e.g. Na 6 Fe 2 S 6 ), is substantiated by a full crystallographic group‐subgroup tree. The crystal chemistry of the new indates is discussed and compared with that of alkali chalcogenido metallates(III) of Fe, Al and Ga containing [ M 2 Q 6 ] 6– dimers, which overall form as many as ten different structure types. DFT band structure calculations of the three title compounds exhibit bandgaps, which continuously decrease from the S to the Te compound and which are also in accordance with the pale yellow (S), bright yellow (Se) and red‐brown (Te) color of the compounds. The chemical bonding in the salts and within the metallate anion is discussed on the basis of the partial DOS and a Bader analysis of the calculated electron density.