Cotemplating Assembly and Structural Variation of Three-Dimensional Open-Framework Sulfides

Abstract

Open-framework sulfides (H 3 O)-KCu 6 Ge 2 S 8 (1) and (H 3 O)RbCu 6 Ge 2 S 8 (2) were prepared by a cotemplating strategy. This shows that alkali-metal and protonated water cations act as cotemplates to direct the three-dimensional open-framework sulfides. These templates direct two types of onedimensional channels that arrange parallelly, and different types of templates reside in different types of channels. By introduction of the Cs cation into the synthetic systems of 1 and 2, (H 3 O)K 0.6 Cs 0.4 Cu 6 Ge 2 S 8 (3) and (H 3 O)-Rb 0.75 Cs 0.25 Cu 6 Ge 2 S 8 (4) were obtained. Compound 3 has a different anionic framework from those of 1 and 2, while 4 is isostructural with 1 and 2.

Open-Framework Chalcogenide (H3O)KCu6Ge2S8·nH2O Exhibiting High Mixed Proton–Electron Conduction

“…As mentioned above, in this study, we made a modification in the preparation process of 1 and used excess amount of sulfur powder in the reactants, while other reaction conditions, such as reaction time, temperature, solvent, and the molar ratios of Cu/GeO 2 /K 2 CO 3 , remained the same as those in the literature . The molar ratio of S/GeO 2 in the reactants was varied from 14.17 to 20.17 in a sequential manner, and the results showed that the amount of unknown impurity in the final product decreased with the increasing molar ratio of S/GeO 2 .…”

“…Although the crystal structure of 1 was previously reported in the literature, herein, it is briefly described for better understanding the conduction. Crystals of 1 belong to a tetragonal system with the space group P 4/ m .…”

“…As shown in Figure b, the GeS 4 /CuS 4 coordination tetrahedra and CuS 3 coordination triangles are connected via vertex sharing to form a 3D anionic open framework of (Cu 3 GeS 4 ) n 2 n – with two types of 1D channels along the c -axis. These two types of channels show cross-sectional areas of d 1 × d 1 = 7.59 × 7.59 Å 2 and d 2 × d 2 = 5.54 × 5.54 Å 2 , which are occupied by H 3 O + and K + ions, respectively . In a channel, a K + ion is surrounded by eight S2 ions with a distance of K–S = 3.324 Å, less than the summation of S 2– and K + ion radii (3.35 Å), since the effective ionic radii are 1.51 Å for K + with a coordination number of 8 and 1.84 Å for S 2– (as displayed in Table S1), indicating the presence of weak coordination bonds between S 2– and K + ions.…”

“…A solvothermal reaction in a Teflon-lined autoclave at 200 °C was used for preparation of 1 in the literature; however, the final product contains unknown impurities, which are almost not dissolved in H 2 O and common organic solvents. Noticeably, in a Li–S battery, sulfur powder is, in general, used to react with S 2– ions to produce S x 2– polysulfide anions in the presence of alkaline amines as illustrated in eq ; moreover, the polysulfide anions as a soft base can easily coordinate with Cu + ions (soft acid) to form soluble complex species, and this will effectively prevent the generation of insoluble copper sulfide, etc., …”

“…The preparation process was previously reported in the literature and modified in this study, i.e ., excess sulfur powder was used in the mixture of reactants although all other reaction conditions were the same as those reported in the literature . The representative procedure can be described as follows.…”