The synthesis, structure, and nonhumidified proton conductivity of the hydrated alkali thiohydroxogermanates, denoted as MxGeSx(OH)4-x·yH2O (1 ≤ x ≤ 4, 0 < y < 8) for M = Na, K, Rb, and Cs, are reported. These materials are generally X-ray amorphous when produced by a low-temperature (75 °C) aqueous solution evaporation−precipitation route. Raman and IR spectroscopies indicate mixed chalcogenide germanium central anions with distinct asymmetric Ge−O and symmetric Ge−S stretching modes observable around 820−754 and 500−325 cm-1, respectively. These thio-oxoanions possess a combination of thermally stable hydroxyl groups and hydrophilic alkali associated with the nonbridging sulfurs. Alternating current impendence measurements performed under anhydrous conditions on low-pressure sealed pellets reveal fast ionic conductivity, 10-3−10-2 S/cm, for typical temperatures between 100 and 275 °C. The observed falloff in conductivity at higher temperatures is consistent with the appearance of endothermic transitions in differential scanning calorimetry measurements of hermetically sealed samples, presumably from the "boiling" or sublimation of a crystalline water sublattice. Corresponding onset temperatures were observed between 150 and 275 °C and dependent on the alkali and composition. The synthesis, structure, and nonhumidified proton conductivity of the hydrated alkali thiohydroxogermanates, denoted as M x GeS x (OH) 4-x ‚yH 2 O (1 e x e 4, 0 < y < 8) for M ) Na, K, Rb, and Cs, are reported. These materials are generally X-ray amorphous when produced by a low-temperature (∼75°C) aqueous solution evaporation-precipitation route. Raman and IR spectroscopies indicate mixed chalcogenide germanium central anions with distinct asymmetric Ge-O and symmetric Ge-S stretching modes observable around 820-754 and 500-325 cm -1 , respectively. These thio-oxoanions possess a combination of thermally stable hydroxyl groups and hydrophilic alkali associated with the nonbridging sulfurs. Alternating current impendence measurements performed under anhydrous conditions on lowpressure sealed pellets reveal fast ionic conductivity, 10 -3 -10 -2 S/cm, for typical temperatures between 100 and 275°C. The observed falloff in conductivity at higher temperatures is consistent with the appearance of endothermic transitions in differential scanning calorimetry measurements of hermetically sealed samples, presumably from the "boiling" or sublimation of a crystalline water sublattice. Corresponding onset temperatures were observed between 150 and 275°C and dependent on the alkali and composition. Under dry atmosphere conditions, thermogravimetric analysis mass loss measurements indicate continuous mass loss above the preparation temperature of ∼75°C.

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The synthesis and structure of the thiogermanic acids H4Ge4S10 and H2Ge4S9 are reported. A novel preparation method consisting of reacting germanium oxide with liquid hydrogen sulfide containing a trace amount of water is used to form Ge4S104-ions. Evaporating the hydrogen sulfide solution at room temperature leaves an unstable H4Ge4S10·xH2O product. The stoichiometry and structure of the thermally stable anhydrous phase are dependent on reaction time. An H4Ge4S10 product with an adamantane-like cage structure is obtained at shorter reaction times. Longer reaction times produce an H2Ge4S9 product with a more complex cage unit, a higher symmetry unit cell, and increased thermal stability. Raman, infrared, powder X-ray diffraction, and thermogravimetric data are reported for both structures.

Using a combination of neutron diffraction, infrared spectroscopy, and first-principles calculations, we have investigated the structure of hydrated and dehydrated proton conducting alkali thio-hydroxogermanates of general formula M2GeS2(OH)2·yH2O (M = K, Rb, and Cs). The results show that the structure of hydrated and dry materials are basically the same, which confirms previous indications that the main effect of heating these materials is just a loss of water. We suggest that in the hydrated state the structure of these materials is built of dimers of thio-hydroxogermanate anions, with the water molecules acting as bridges between such dimers. In the dehydrated structure, the thio-hydroxogermanate anions instead form an extended network through the formation of interdimer hydrogen bonds through the −OH groups in the structure. The alkali ions are suggested to act as "space-fillers" in voids formed by the thio-hydroxogermanate anion dimers, in both the hydrated and the dehydrated state. Disciplines Inorganic Chemistry | Materials Chemistry | Materials Science and Engineering CommentsReprinted with permission from Chemistry of Materials 20 (2008) Using a combination of neutron diffraction, infrared spectroscopy, and first-principles calculations, we have investigated the structure of hydrated and dehydrated proton conducting alkali thio-hydroxogermanates of general formula M 2 GeS 2 (OH) 2 · yH 2 O (M ) K, Rb, and Cs). The results show that the structure of hydrated and dry materials are basically the same, which confirms previous indications that the main effect of heating these materials is just a loss of water. We suggest that in the hydrated state the structure of these materials is built of dimers of thio-hydroxogermanate anions, with the water molecules acting as bridges between such dimers. In the dehydrated structure, the thio-hydroxogermanate anions instead form an extended network through the formation of interdimer hydrogen bonds through the -OH groups in the structure. The alkali ions are suggested to act as "space-fillers" in voids formed by the thiohydroxogermanate anion dimers, in both the hydrated and the dehydrated state.