Synthesis and Characterization of RbLi7Ge8 with Isolatedcloso-[Li4Ge12]8− Ions, Lithium-Capped Truncated Tetrahedra of Ge1212−

Abstract

Kappt man die vier Spitzen eines Tetraeders, so gelangt man zur Struktur von Ge1212−, dem größten isolierten Cluster eines Elements der 14. Gruppe (siehe Bild). Dieser Cluster liegt in der salzartigen Zintl‐Phase RbLi7Ge8 vor. Durch Erhitzen der Elemente im stöchiometrischen Verhältnis wurde diese Verbindung erhalten.

Li18Na2Ge17—A Compound Demonstrating Cation Effects on Cluster Shapes and Crystal Packing in Ternary Zintl Phases

“…Such [Ge 12 ] 12− truncated tetrahedra have been reported once before in the related Zintl phase Li 7 RbGe 8 , in which they occur next to tetrahedral [Ge 4 ] 4− . 4 Similar [Sn 12 ] 12− clusters are observed in ENa 10 Sn 12 (E = Ca, Sr). 31 Larger Ge polyanions have only been isolated via soluble [Ge 9 ] 4− , with [Ge 45 ] 12− being the largest example of covalently linked Ge atoms.…”

“…The crystal structure of Li 18 Na 2 Ge 17 is closely related to the structure of Li 7 RbGe 8 . 4 In both compounds, the Li-centered Friauf polyhedra [Li@Li 4 Ge 12 ] 7− arrange in a hexagonally primitive fashion, as demonstrated in Figure 2. The resulting voids are filled by [Ge 4 ] 4− tetrahedra and in the case of Li 18 Na 2 Ge 17 also by isolated Ge anions.…”

“…Due to the lower crystal symmetry, Ge−Ge bond lengths (2.4840(5)−2.6948(5) Å) vary in a greater range than in Friauf polyhedra in Li 7 RbGe 8 (2.505(2)−2.603(2) Å). 4 However, average Ge−Ge bond lengths are identical (2.567(1) Å for Li 18 Na 2 Ge 17 , 2.569(2) Å for Li 7 RbGe 8 ). Similarly, the average interatomic distances of Ge and capping Li atoms (2.91(1) Å for Li 18 Na 2 Ge 17 , 2.96(2) Å for Li 7 RbGe 8 ) as well as the interatomic distances of centering Li1 to all 16 surrounding atoms (2.99(1) Å for Li 18 Na 2 Ge 17 , 3.02(2) Å for Li 7 RbGe 8 ) fall in the same ranges (Table 2).…”

“…A single-crystal X-ray structure determination shows that the novel Zintl phase Li 18 Na 2 Ge 17 contains the largest known anionic cluster unit, [Ge 12 ] 12− , which has been observed in only one other compoundthe structurally related Li 7 RbGe 8 . 4 Moreover, Li ). 20 Rather complex Zintl phases with various anions of different sizes require an equally complex and efficient coordination by cations.…”

“…Ge cluster anions range from Br 2 -like [Ge 2 ] 6− dumbbells in BaMg 2 Ge 2 2 and P 4analogous [Ge 4 ] 4− tetrahedra in A 4 Ge 4 (A = Na, K, Rb, Cs) 3 to truncated tetrahedra [Ge 12 ] 12− in Li 7 RbGe 8 . 4 Some examples of such Ge Zintl anions are depicted in Figure 1. Isolated Ge 4− anions with noble-gas configurations are frequently observed as well: for example, in compounds E 2 Ge (E = Mg, Ca, Sr, Ba).…”