The Ga/In phase width (y) and the distribution of the two triels within the polyanions of known binary (x = 1, 2) and new ternary ‘intermediate’ (x = 1–2) alkali trielides Ax(Ga1−yIny)3 (A = K, Rb, Cs) was investigated in a synthetic (slow cooling of the melts of the three elements), crystallographic (X-ray single crystal) and bond theoretical (FP-LAPW DFT bandstructure calculation) study. The Cs2In3-type structure (x = 2, series A, tetragonal, I 4/mmm) exhibits layers of four-connected closo octahedra [M6]4−. Ternary K compounds of this type were yielded within a large range (y = 0–0.87), whereas isotypic Rb/Cs trielides exist only at higher In contents (>52/69%). Geometric criteria determine not only the Ga/In stability ranges but also the occurrence of a commensurate superstructure at approx. 33% In (K2Ga2.17In0.83: P 42/ncm, a = 879.83(4), c = 1557.66(10) pm, R 1 = 0.0887), in which the octahedra are slightly tilted against the layers. Cesium compounds of the RbGa3-type structure (x = 1, C, tetragonal, I 4̅m2), which exhibits a 3D network of all-exo bonded closo dodecahedra [M8]2− and four-bonded M− anions, are stable throughout the whole substitutional range CsGa3–CsIn3. The maximum possible In content increases with increasing size of A+ (Cs: 100%, Rb: 30%, K: 8% In). The similarities between these two tetragonal structures are consistent with the occurrence of two new structure types of ‘intermediate’ compounds A7M15 (x = 1.4, 1B/2B), which differ in the stacking sequences of double layers of novel six-fold exo-bonded pentagonal bipyramidal closo clusters [M7]3− connected via four-bonded M− (e.g. 1B: Cs7Ga8.4In6.6, P 4̅m2, a = 656.23(3), c = 1616.0(1) pm, R 1 = 0.0742; 2B: Rb7Ga8.1In6.9, P 42/nmc, a = 665.64(2), c = 3140.9(2) pm, R 1 = 0.0720). The Rb/Cs compounds of these types are only stable in a limited Ga/In region and with a distinct Ga/In distribution within the [M7] clusters. According to the close relation between the structures A, B and C, the structure family is characterised by the occurrence of stacking faults and diffuse scattering, indicating the existence of further members of this series. The new compound Cs5Ga3.1In5.9 (x = 1.667, P 4̅m2, a = 654.62(2), c = 3281.5(2) pm, R 1 = 0.1005) is a reasonably periodically ordered stacking variant containing layers A and double layers B in parallel.

Abstract. The new cluster compound K 3 Ga 11-x In x , 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, R 1 = 0.0471]. In the complex polyanion, the triels form two crystallographically different [Ga 12 ] icosahedra, which are present in a 1:2 ratio, and a previously unknown [M 13 ] "double-cluster" consisting of two vertex-sharing [M 7 ] pentagonal bipyramids. All clusters are connected among each other and via a four-bonded pure In and Ga

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The Ga-rich gallides of the alkali metals present an interesting, yet still scarcely investigated case of polyanionic cluster compounds with subtle variations in the character of their chemical bonding. In the present work, the Ga richest phases K3Ga13, RbGa7, and CsGa7, which are formally electron-precise Zintl/Wade cluster compounds, are systematically studied with respect to a partial substitution of Ga by In and Hg. The pure hepta-gallides AGa7 (A = Rb/Cs; R3¯m), which were formerly obtained from Ga-rich melts in powder form only, were crystallized from Hg-rich melts. Herein, up to 9.9/13.6% (Rb/Cs) of Ga could be substituted by In, which partly takes the four-bonded [M2] dumbbells connecting layers of Ga-icosahedra. Even though the structures are electron precise, the pseudo band gap does not coincide with the Fermi level. In the most Ga-rich potassium compound K3Ga13 (Cmcm) only 1.2% of In and 2.7% of Hg could be incorporated. Although Rb3Ga13 remains unknown, ternary variants containing 5.2 to 8.2% In could be obtained; this structure is also stabilized by a small Hg-proportion. The likewise closed-shell 3D polyanion consists of all-exo-bonded Ga-icosahedra and closo [Ga11] clusters, which are connected by two tetrahedrally four-bonded Ga− and a trigonal-planar three-bonded Ga0. The aspects of the electronic structures and the site-specific Ga↦Hg/In substitution in the polyanion (“coloring”) are discussed for the title compounds and other mixed Ga/In trielides.

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