Unusual Flexibility of Microporous Sulfides during Ion Exchange

Abstract

Open-framework chalcogenides with ion-exchange capacity are promising materials for removing hazardous heavymetal ions and for capturing radioactive Cs + . However, research on the exchange mechanism is limited, especially for the framework chalcogenides that have multiple bridging anions. Generally, openframework chalcogenides that have multiple bridging anions at the window or wall of the channels are rigid during the ion-exchange process. We show here that microporous sulfides with μ 3 -S 2− (where μ 3 = triple bridging mode) at the windows exhibit framework flexibility upon ion exchange. Three new microporous sulfides Na 4 Cu 8 Ge 3 S 12 •2H 2 O (1), Na 3 (Hen)Cu 8 Sn 3 S 12 (where en = ethylenediamine) (2) and (dap) 2 (Hdap) 4 Cu 8 Ge 3 S 18 (where dap = 1,2-diaminopropane) (3) were synthesized under solvothermal conditions. Compounds 1 and 2 contain a copper-rich framework composed of icosahedral [Cu 8 S 12 ] 16− units linked via monomeric GeS 4 4− or SnS 4 4− tetrahedral units, whereas compound 3 features an expanded framework composed of icosahedral [Cu 8 S 12 ] 16units interconnected with dimeric Ge 2 S 6 4− units. These compounds exhibit unusual ion-exchange properties. Specifically, the frameworks of 1 and 2 (with μ 3 -S at the small windows) show "breathing action" upon ion exchange of K + or Rb + , which have relative large sizes, and compound 3 exhibits framework flexibility upon Cs + ion exchange with both space group and channels changed.

Two-Step Reaction Mechanism of Roasting Spodumene with Potassium Sulfate

“…The concurrent deviation from the linear thermal expansion of α-spodumene between 780 and 850 °C demonstrates that the presence of potassium sulfate results in a transient increase in the spodumene unit cell volume (Figure d). This distortion of the spodumene structure and the associated increase in peak intensity (Figure ) is consistent with a topotactic exchange of larger potassium ions (1.33 Å) with a higher X-ray scattering factor for lithium ions (0.78 Å) in the intact spodumene crystal structure. − K occupancy of the spodumene M2 site reaches a maximum of 11 ± 1% at 850 °C, providing further evidence for ion exchange as the first step of the reaction between spodumene and potassium sulfate. The significantly larger average M2–O bond length in α-(Li, K)-spodumene compared to α-spodumene demonstrates that the incorporation of K leads to expansion of the M2 cation site, consistent with previous studies of K incorporation into pyroxenes. − The potassium uptake into Mg-Ca pyroxene diopside (MgCaSi 2 O 6 ) is commonly coupled to the incorporation of a trivalent cation into the M1 site and to splitting of the M2 site, both of which counterbalance the effects of expansion in the M2 site. ,, No such counterbalancing is present in the spodumene structure in which the M1 site expands as well, consistent with the abnormal thermal expansion observed in the ion exchange region between 780 and 850 °C.…”

Size-Driven Stability of Lanthanide Thiophosphates Grown from an Iodide Flux

“…The pervasive interest in main group, transition, and rare earth metal sulfide chemistry is driven by their structural diversity and unique properties. − Replacing hard Lewis base oxide ligands with soft sulfides leads to a change in the bonding between the metal center and the ligand resulting in changes in the optical, magnetic, and structural properties of the materials. − Recently, particular interest has been directed toward thiophosphate materials that exhibit conducting and catalytic properties. , For example, a family of layered thiophosphate materials with a general formula MPS x , such as MnPS 3 , NiPS 3 , and ZnPS 3 , can be readily exfoliated and exhibits antiferromagnetic transitions at temperatures below 120 K. − Layered thiophosphites have shown potential for application in hydrogen evolution reactions and other energy applications. , Lithium and sodium thiophosphates, in particular, possess outstanding diffusion properties making them a potential class of materials for ion conduction applications and, as a result, have generated significant interest to comprehensively investigate these materials. ,− …”

Sodium-Stuffed Open-Framework Quaternary Chalcogenide Built with (Cu2Ga6S18)16– Ribbons Cross-Linked by Unusual Linear Cu(I) Pillars

“…The most prevalent coordination of Cu + in complex chalcogenides and in open-framework materials is planar trigonal and tetrahedral. The planar trigonal coordination often leads to an icosahedral cluster of Cu–S in many open-framework materials. ,,,, Whereas a tetrahedral coordination of Cu + can be an integral part of the supertetrahedral building unit, ,, there are only a handful of examples in open-framework materials in which Cu + is in linear coordination as seen in organically templated CuGe 2 S 5 ·(C 2 H 5 ) 4 N, where Ge 4 S 10 -T2 supertetrahedral units are exclusively connected by linear S–Cu–S linkages. In another example, Cu + is both part of supertetrahedra and the linear coordination connecting the supertetrahedra .…”

“…All of these attributes make a perfect playground for solid-state chemists to investigate chalcometallates in combination with transition metals. Among the transition metals, Cu and Ag possess unique characteristics in chalcogenide solid-state chemistry ascribed to their ability to adopt different coordination environments. , A large number of open-framework chalcogenides with copper have been synthesized hydro- and solvothermally, where the role of copper has been pivotal in forming certain building units, e.g., icosahedra or supertetrahedra, in linking the building units and/or clusters, etc. ,− More importantly, Cu also modulates the band structure of the compound, where Cu d states contribute close to the Fermi level and tune the band gap of chalcometallates. However, under purely solid-state synthetic conditions at moderately high temperatures, the role of copper in building a specific structural component has not been explored extensively, especially in combination with Ga-chalcogenide networks.…”