Thermally stable self-assembling open-frameworks: Isostructural Cs+ and (CH3)4N(+) iron germanium sulfides

Here we report on investigations that have revealed for the first time that the Cs+ ion templates the same metal germanium sulfide open-framework as (CH3N+ (TMA(+)), and that metal complexing agents enhance crystal size by at least two orders of magnitude. The synthesis, structures and thermal properties of Cs2FeGe4S10 . x H2O and TMA(2)FeGe(4)S(10) are also described. Both have 3D zinc blende-type open-framework structures. These materials have the same connectivity as TMA(2)MnGe(4)S(10). The tetrahedral sites in the lattice are alternately substituted by pseudo-tetrahedral Fe-2+ and adamantanoid Ge4S104- building blocks, covalently linked together by Fe(mu-S)Ge bridge bonds, to give a tetragonal unit cell. The charge-balance of the anionic framework [FeGe4S10](2-) is maintained by either Cs+ or TMA(+) ions in the cavity spaces. Synthesis of these materials demonstrates an interesting example of a self-assembly process in which a 3D framework is built from molecular precursors. Water adsorption-desorption cycling from room temperature to 200 degrees C reveals framework flexibility between larger and smaller tetra- gonal unit cell I (4) over bar isotypes. The compound TMA(2)FeGe(4)S(10) is stable in nitrogen at 350 degrees C and under vacuum at 450 degrees C. The corresponding temperatures for Cs2FeGe4S10 are 530 degrees C and 630 degrees C; it is stable on cooling to room temperature under vacuum, and after subsequent exposure to air. Six hundred thirty degrees celsius is the highest recorded temperature at which the integrity of a non-oxide framework has been maintained. The framework stability and flexibility of ''all-inorganic'' Cs2FeGe4S10 provides an encouraging example for researchers interested in developing sulfide-based framework materials with practical applications.