Synthesis and crystal structure of Ae2LiInGe2 (Ae = Ca, Sr):: New zintl phases with a layered silicate-like network

Two new Zintl phases Ae(2)LiInGe(2) (Ae = Ca 1; Sr 2) were obtained from stoichiometric reactions of the pure elements in sealed Nb tubing at 1000 -1050 degreesC. The isomorphous polar intermetallic phases crystallize in the orthorhombic space group Pnma, with cell constants of a = 7.2512(7), b = 4.4380(5), and c = 16.902(1) Angstrom for compound 1, and a = 7.5033(8), b = 4.6194(5), and c = 17.473(2) Angstrom for compound 2. The crystal structure can be derived from the vertex-sharing of InGe4/2 tetrahedral units that form "corrugated" sheets normal to the crystallographic c-axis. Calcium and lithium atoms act as "spacers" that effectively separate the anionic [InGe2](5-)-layers. The layered anionic substructure is similar to those exhibited by layered metal oxides, sulfides, and silicates. The connectivity of the tetrahedral building unit, [InGe4/2](5-), is analogous and isoelectronic to the silicate [SiO4/2] unit.