BINARY ALKALI-METAL COMPOUNDS WITH THE ZINTL ANIONS [GE-9](4-) AND [SN-9](4-)

The binary germanides M12Ge17 and M4Ge9 (M = Na, K, Rb, Cs) and the st annides M12Sn17 and M4Sn9 (M = K, Rb, Cs) were identified by a combina tion of direct synthesis, thermogravimetric analysis, Vibrational spec troscopy, X-ray powder data and single crystal structure analysis. The M12E17 phases contain the cluster anions [E-9](4-) and [E-4](4-) in t he ratio 1:2, forming a hierarchical structure with the cluster anions at the atomic positions of the hexagonal Laves phase MgZn2. Like the M4E4 phases, the M4Ge9 compounds are hierarchical derivatives of the c ubic Cr3Si structure but with [Ge-9](4-) anions. The thermogravimetric analyses give strong evidence for the existence of at least one more phase with [E-9](4-) and [E-4](4-) clusters and of the clathrate phase s M6E25 and MxE136 in addition to the well-known M(8)E(44)square(2) ch lathrates.