Mesostructured metal germanium sulfide and selenide materials based on the tetrahedral [Ge₄s₁₀]^4- and [Ge₄Se₁₀]^4- units: Surfactant templated three-dimensional disordered frameworks perforated with worm holes

The polymerization of [Ge₄S₁₀]^4- and [Ge₄Se₁₀]^4- unit clusters with the divalent metal ions Zn²⁺, Cd²⁺, Hg²⁺, Ni²⁺, and Co²⁺ in the presence of various surfactant cations leads to novel mesostructured phases. The surfactants are the quaternary ammonium salts C₁₂H₂₅NMe₃Br, C₁₄H₂₉NMe₃Br, C₁₆H₃₃NMe₃Br, and C₁₈H₃₇NMe₃Br, which play the role of templates, helping to assemble a three-dimensional mesostructured metal-germanium chalcogenide framework. These materials are stoichiometric in nature and have the formula of (R-NMe₃)₂[MGe₄Q₁₀] (Q = S, Se). The local atomic structure was probed by X-ray diffuse scattering and pair distribution function analysis methods and indicates that the adamantane clusters stay intact while the linking metal atoms possess a tetrahedral coordination environment. A model can be derived, from the comparison of measured and simulated X-ray powder diffraction patterns, describing the structure as an amorphous three-dimensional framework consisting of adamantane [Ge₄Q₁₀]^4- units that are bridged by tetrahedral coordinated M²⁺ cations. The network structures used in the simulations were derived from corresponding disordered structures developed for amorphous silicon. The frameworks in (R-NMe₃)₂[MGe₄Q₁₀] are perforated with worm hole-like tunnels, occupied by the surfactant cations, which show no long-range order. This motif is supported by transmission electron microscopy images of these materials. The pore sizes of these channels were estimated to lie in the range of 20-30 Å, depending on the appointed surfactant cation length. The framework wall thickness of ca. 10 Å is thereby independent from the surfactant molecules used. Up to 80% of the surfactant molecules can he removed by thermal degradation under vacuum without loss of mesostructural integrity. Physical, chemical, and spectroscopic properties of these materials are discussed. (C) 2000 Academic Press.