Synthesis and revised structure of the Zintl phase Li7Ge12

The structure of the binary Zintl phase Li7Ge12 has been revised. A good-yield synthesis of Li7Ge12 has been elaborated by the reaction of the elements in stoichiometric amounts using an arc melter. Subsequent annealing led to a single-phase product, and single crystals suitable for an X-ray structure determination were obtained using a high-frequency oven. The reinvestigation of the as yet only roughly described crystal structure of Li7Ge12 reveals an isotypic relationship with Na7Sn12. Li7Ge12 can be described as an ordered model by using a monoclinic metric and a twin model pretending an orthorhombic symmetry (space group P2/n (no. 13) with a = 11.527(5), b = 8.301(1), c = 15.354(2) Å, ß = 90.00(1)°, and V = 1421.2(3) Å3; R1 = 0.058, wR2 = 0.117 for all data). The structure consists of two-dimensional slabs of covalently bonded Ge atoms. The slabs are layered with Li atoms, which also fill the larger channels of the Ge slabs. The structure thus determined shows none of the problems observed in a former structure determination, like inconsistent interatomic distances and very large atomic displacement parameters.

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