The New Mixed Cluster Trielide K3Ga11–xInx (x = 1.16–1.36): Synthesis, Crystal Chemistry, and Chemical Bonding

Abstract

The new cluster compound K3Ga11–xInx, which exhibits a very small In/Ga phase width of x = 1.16 to 1.36 only, was obtained in the course of a systematic synthetic, crystallographic and bond theoretical investigation of mixed potassium trielides of the ternary system K‐In‐Ga. The compound, which was synthesized from nearly stoichiometric amounts of the elements at a maximum temperature of 500 °C, crystallizes in a new orthorhombic crystal structure type [space group Cmmm, a = 1577.9(5), b = 3355.1(8), c = 655.2(2) pm, Z = 10, R1 = 0.0471]. In the complex polyanion, the triels form two crystallographically different [Ga12] icosahedra, which are present in a 1:2 ratio, and a previously unknown [M13] “double‐cluster” consisting of two vertex‐sharing [M7] pentagonal bipyramids. All clusters are connected among each other and via a four‐bonded pure In and Ga atom [In(1), Ga(1)]. The polyanion of the compound with the overall formula K15M55 can thus be split up according to [Ga(1X)12][Ga(2X)12]2[M(3X)13]In(1)4Ga(1)2. Herein, the all‐exo bonded closo icosahedra carry a charge of –2, the six four‐bonded In/Ga contribute with a charge of –6 and the new [M13] “double‐cluster” thus carries a charge of –3. Under the reasonable assumption of an “intermediate” interaction between the two cluster fragements, this charge, i.e. the presence of 15 skeleton electron pairs, is in accordance with the mno electron counting rules. FP‐LAPW DFT band structure calculations of two ordered model compounds support this interpretation: The tDOS exhibits a small bandgap and the electron density map suggests a limited additional interaction between the Ga5 bases of the two bipyramidal cluster fragments.