Facile Amine-Surfactant Thermal Syntheses, Structures, and Properties of Novel Crystalline Silver Thioantimonates

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2017-05-04

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Abstract

Complex silver thioantimonates previously synthesized in supercritical ammonia leads to quaternary silver thioantimonates(V), while silver thioantimonates(III) are prepared via solvothermal processes. This collection of compounds exhibits diverse structural chemistry with architectures from linear chains to three-dimensional frameworks. This research is motivated by the discovery of new silver thioantimonates(III) using a different media. Our exploratory research led to the discovery of new silver thioantimonates(III) utilizing the amine-PEG400 thermal synthetic route. In this dissertation, we report the syntheses, structures, and properties of I-NH4AgSb2S4, II-(NH4)0.88Rb0.12AgSb2S4, III-(NH4)0.86Rb0.137AgSb2S4, IV-NH4AgSb4S7•H2O, V-(NH4)0.67Rb0.33AgSb4S7•H2O, VI-CsAgSb4S7, VII-(C4N2H12)0.5Ag2SbS3, and VIII-(C4N2H12)Sb8S14. Compound I features parallel anionic [AgSb2S4]- sheets separated by NH4+ cations. Meanwhile, compound IV features a three-dimensional framework with large channels occupied by H2O and NH4+. These compounds are new examples of low Ag/Sb ratio silver thioantimonate(III) compounds. The charged-balancing NH4+ are formed in-situ from the disproportionation of hydrazine in aerobic, basic aqueous conditions. These compounds can be synthesized at stoichiometry and can be obtained in high yields through careful control of the hydrazine concentration. The Rb-derivatives II, III, and V were synthesized in the presence of Rb2SO4 in the reaction mixture. Partial substitution of NH4+ by Rb+ cations did not offer any significant structural changes. Based on the solvent’s chemistry, it is our belief that pure alkali-metal analogs can be synthesized using anhydrous hydrazine. Furthermore, the successful synthesis of VI under amine-PEG400 thermal conditions indicate that the current process is a more efficient, convenient, inexpensive, and scalable alternative to the reactive flux method in synthesizing new transition metal chalcogenidometallates. Compounds VII and VIII are new inorganic-organic hybrid compounds obtained from reactions in piperazine-PEG400 mixed-solvent. Their anionic substructures are charge-balanced by diprotonated piperazine cations. The layered structure found in VII is similar to other compounds based on the [Ag2SbS3]- anion. The structural similarity among silver thioantimonates(III) synthesized in organic amines indicate that these compounds can potentially be tuned in the same way that organic amines tune the structure and properties of metal halides. The compounds presented herein are new silver thioantimonate(III) semiconductors with direct band gaps of 1.94, 1.93, 1.92, 1.95, 1.91, 2.07, and 2.13 eV for I-VII, respectively.

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Silver thioantimonates, Chalcogenides

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