Li18Na2Ge17--a compound demonstrating cation effects on cluster shapes and crystal packing in ternary Zintl phases.
The novel ternary Zintl phase Li18Na2Ge17 was synthesized from a stoichiometric melt and characterized crystallographically. It crystallizes in the trigonal space group P31m (No. 157) with a = 17.0905(4) Å, c = 8.0783(2) Å, and V = 2043.43(8) Å(3) (final R indices R1 = 0.0212 and wR2 = 0.0420 for all data). The structure contains three different Zintl anions in a 1:1:1 ratio: isolated anions Ge(4-), tetrahedra [Ge4](4-), and truncated, Li-centered tetrahedra [Li@Ge12](11-), whose hexagonal faces are capped by four Li cations, resulting in the Friauf polyhedra [Li@Li4Ge12](7-). According to the Zintl-Klemm concept, Li18Na2Ge17 is an electronically balanced Zintl phase, as experimentally verified by its diamagnetism. The compound is structurally related to Li7RbGe8, which also contains [Ge4](4-) and [Li@Li4Ge12](7-) in its anionic substructure. However, exchanging the heavier alkali metal cation Rb for Na in the mixed-cation germanides leads to drastic changes in stoichiometry and crystal packing, demonstrating the great effects that cations exert on such Zintl phases through optimized cluster sheathing and space filling.
Department Chemie, Technische Universität München , Lichtenbergstraße 4, 85747 Garching b. München, Germany.
Lavinia M
LM
Scherf
Michael
M
Zeilinger
Thomas F
TF
Fässler