Reported here is the deep eutectic solvothermal synthesis of an open framework copper selenidogermanate [NH3CH3]0.75Cu1.25GeSe3 (CuGeSe-1), which shows a pH-resistant Cs+ ion exchange performance (qm = 225.3 mg g−1).

Deep eutectic solvents (DESs) have been adopted as reaction media for solvothermal synthesis of crystal materials. In the present work, we extended the scope of DESs in chalcogenidometalate preparation by including dimethylamine, ethylamine, and trimethylamine hydrochlorides and synthesized a series of novel Sn-Se and Ag-Sn-Se compounds: i.e., [NH2(CH3)2]2Sn3Se7·0.5NH­(CH3)2 (1), [NH4]2Sn4Se9 (2), [NH3C2H5]2Sn3Se7 (3), and [NH4]3AgSn3Se8 (4). Compounds 1 and 3 possess honeycomb lamellar [Sn3Se7] n 2n– structures featuring large hexagonal windows, while compound 2 features a rare [Sn4Se9] n 2n– anionic layer consisting of tetrameric {Sn4Se10} clusters as secondary building units (SBUs). Compound 4 comprises infinite [AgSn3Se8] n 3n– chains built by {Sn3Se8} units with Ag+ linkers, and it represents the first heterometallic chalcogenide synthesized in DESs. The organic ammonium cations of halide salts or in situ formed ammonium cations from the decomposition of urea act as templating agents for the formation of the inorganic frameworks. Compound 4 exhibits a marked thermochromic performance in the visible light range owing to the negative temperature dependence of its band gap (E g = 2.305–2.119 eV in the range of 100–450 K). The gold−dark red−gold color change is highly reversible in five rounds of heating and cooling, without any phase transition of the material, shedding light on the consequent device innovations.

Rational synthesis of inorganic matter remains a great challenge encountered with modern synthetic chemistry. Here we reported the stepwise solvothermal conversion from GeO2 to [MGe4S10] n 3n– (M = Cu, Ag) polymer via isolatable [Ge2S6]4– and [Ge4S10]4– anions by virtue of templating technique. The facile sulfuration of GeO2 resulted in the methylammonium-templated dimeric thiogermanate [CH3NH3]4­Ge2S6 (1). This was used subsequently as a precursor for the formation of adamantane-like [Ge4S10]4– cluster, which was isolated as a mixed methylammonium/ethylammonium salt [CH3CH2NH3]3­[CH3NH3]­Ge4S10 (2). Compound 2 was then successfully used as a precursor to react with Cu+ and Ag+ cations in the presence of tetraethylammonium, resulting in alternating copolymeric products [(CH3CH2)4N]3­MGe4S10 (M = Cu (3), Ag (4)), whose anionic moieties feature a novel zigzag chainlike structure constructed by [Ge4S10]4– clusters via two-coordinate Cu+/Ag+ linkers. Mixed amine/ethanol or deep eutectic solvents were applied as media for the syntheses of 1–4, and all the products were characterized in the solid state and solution. Crystal structural analysis of the title compounds revealed significant templating roles of the alkylammonium cations as both space-filling agents and hydrogen-bonding donors, suggesting the structure-directing mechanism for the species formation and crystal growth. The design and optimization of multistep structural conversion upon templating effects would be beneficial for drawing rational, predictable pathways for inorganic synthesis.