Cs 4 Ge 9 · en : A Novel Compound with [Ge 9 ] 4− Clusters – Synthesis, Crystal Structure and Vibrational Spectra

Red‐orange prismatic crystals of Cs 4 Ge 9 · en ( en = ethylenediamine) were obtained via metathesis reaction of an en solution of K 4 Ge 9 with a large excess of CsI. The compound is very sensitive to air and moisture. Cs 4 Ge 9 · en is not isotypic to Rb 4 Ge 9 · en and crystallizes in a new structure type (monoclinic, space group P 2 1 / c (No. 14); a = 16.757(3), b = 16.462(3), c = 15.657(2) Å, β = 90.37(1)°; Z = 8; Pearson code mP 200). The crystal structure comprises two types ( A and B ) of discrete [Ge 9 ] 4− units arranged in the motif of a distorted hexagonal close‐packing (h.c.p.). In this h.c.p. framework, each tetrahedral hole is filled by one Cs atom and each larger octahedral hole is filled by a group of one en and two Cs atoms. The topology of the two crystallographically distinct [Ge 9 ] 4− clusters corresponds to distorted, monocapped tetragonal antiprisms with bond lengths varying in the range 2.551–2.848Å (type A cluster) or in the range 2.538–2.975Å (less regular type B cluster). According to the DTA and TG measurements, Cs 4 Ge 9 · en decomposes at 378 K under liberation of gaseous ethylenediamine yielding Cs 4 Ge 9 . The Raman spectra of the title compound were interpreted based on the idealized C 4ν symmetry of an isolated [Ge 9 ] 4− cluster. The characteristic breathing mode was localized at 222 cm −1 . The results are analyzed and discussed in context with those of the previously reported compounds Cs 4 Ge 9 , K 4 Ge 9 and Rb 4 Ge 9 · en .