CS4GE9 center dot en: a novel compound with [GE-9](4-) clusters - synthesis, crystal structure and vibrational spectra

Abstract

Red-orange prismatic crystals of CS4Ge9.en (en = ethyl-enediamine) were obtained via metathesis reaction of an en solution of K4Ge9 with a large excess of CsI. The compound is very sensitive to air and moisture. CS4Ge9.en is not isotypic to Rb4Ge9.en and crystallizes in a new structure type (monoclinic, space group P2(1)/c (No. 14); a = 16.757(3), h = 16.462(3), c = 15.657(2) angstrom, beta = 90.37(1)degrees; Z = 8; Pearson code mP200). 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 tilled 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 2.551-2.848 angstrom (type A cluster) or in the range 2.538-2.975 angstrom (less regular type B cluster). According to the DTA and TG measurements, CS4Ge9.en decomposes at 378 K under liberation of gaseous ethylenediamine yielding CS4Ge9. The Raman spectra of the title compound were interpreted based on the idealized C-4v symmetry of an isolated [Geg](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 CS4Ge9, K4Ge9 and Rb4Ge9.en.