Endohedral Ten‐Vertex Clusters [Ga@Tl₁₀]⁸⁻ in the Mixed Trielides A₈GaTl₁₀ (A=K, Rb, Cs)

Abstract

The mixed Ga/Tl trielides A8GaTl10 (A=K, Rb, Cs), which were yielded from stoichiometric melts of the elements, crystallize in the tetragonal K8ZnIn10‐type structure (SG P4/nnc, a=1018.58(3)/1047.14(6)/1077.74(10), c=1363.71(5)/1400.07(8)/1435.4(2) pm, Z=2, R1=0.0187/0.0209/0.0218 for A=K/Rb/Cs). The structures contain isolated ten‐vertex endohedral Ga‐centered clusters [Ga@Tl10]8−, in which the Tl atoms adopt a bicapped square antiprismatic shape. Although the crystallographic point group is 422 only, the cluster shape deviates only slightly from the ideal 8‾ ${\bar 8}$ m2 (D4d) symmetry. The Ga−Tl distances of the two axial Tl(1) atoms are with 305 to 312 pm significantly longer than the eight Ga−Tl(2) bonds (approx. 290 pm). The clusters are enclosed by a shell of 24 (4 : 8 : 8 : 4) alkali cations. For K8GaTl10 and the Zn‐analog K8ZnTl10 the band structures were calculated within the framework of the APW+lo DFT method. Whereas the electron precise 10d+40 valence electron zinc compound exhibits the expected small band gap, the 41 v.e. cluster in K8GaTl10 is a radical with a half‐occupied band crossing the Fermi level. As shown from energy‐selected electron density plots, the large DOS at the Fermi level results from a half‐occupied a1 state dominated by apical Tl(1) pz contributions, which is consistent with molecular DFT studies for related ten‐vertex clusters. The bonding features in the Ga‐centered 41 v.e. clusters of the title compounds are thus intermediate between the 10d+40 Zn‐trielide [Zn@Tl10]8− and the 10d+42 v.e. systems like [Ni@Pb10]2−.

[Tl7]7– Clusters in Mixed Alkali Metal Thallides Cs7.29K5.71Tl13 and Cs3.45K3.55Tl7

“…Alkali metal thallides can be described as materials at the frontier between ionic and intermetallic nature. , While a low amount of alkali metal of less than 50% results in the formation of rather metallic compounds, − increasing proportions lead to the formation of salt-like materials. The observed thallium subunits can then be well described by using the Zintl–Klemm formalism. − The first structurally characterized Zintl phase goes back to E. Zintl himself, who reported on the synthesis and characterization of textbook-known NaTl in the early 1930s .…”