Ionic Liquid-Driven Formation of and Cation Exchange in Layered Sulfido Stannates - a CH2 Group Makes the Difference

Structural Expansion and Enhanced Photocurrent Conversion of Selenido Stannates with Cu+ Ions

As a means of tuning the electronic properties of tin-chalcogenide-based compounds, we present a strategy for the compositional and structural expansion of selenido stannate frameworks under mild conditions by introducing Cu+ ions into binary anionic Sn/Se aggregates in ionothermal reactions. The variable coordination modes of Cu+-contrasting with tetrahedral {SnSe4} or trigonal bipyramidal {SnSe5} units-and corresponding expansion toward ternary Cu/Sn/Se substructures helped to add another degree of freedom to the nanoarchitectures. As desired, the variation of the structural features was accompanied by concomitant changes of the physical properties. Upon treatment of alkali metal salts of the [SnSe4]4- anion at slightly elevated temperatures (120 or 150 °C) in ionic liquids, we isolated a series of compounds comprising ternary or quaternary cluster molecules or networks of cluster units, (C2C2Im)9Li[Cu10Sn6Se22] (1), (C2C2Im)4[Cu8Sn6Se18] (2), (C2C1Im)3[Cu5Sn3Se10] (3), and (C2C2Im)5[Cu8Sn6Se18F]·(C2C2Im)[BF4] (4; C2C2Im = 1,3-diethyl-imidazolium, C2C1Im = 1-ethyl-3-methyl-imidazolium), which were investigated in terms of their optical gaps and photocurrent conversion properties. As illustrated by the synthesis and characterization of an additional salt that does not include Cu+, {(C2C2Im)2[Sn3Se7]}4·{(C2C2Im)[BF4]}2 (5), the significant role of Cu+ in this system was shown to be 3-fold: (a) structural expansion, (b) narrowing of the optical gap, and (c) photocurrent enhancement. By this three-in-one effect, the work offers an in-depth understanding of chalcogenido metalate chemistry with atomic precision.

Layered Thiostannates with Distinct Arrangements of Mixed Cations for the Selective Capture of Cs+, Sr2+, and Eu3+ Ions

The selective capture of radioactive cesium, strontium, and lanthanides from liquid nuclear waste is of great significance to environmental remediation and human health. Herein, the rapid and selective removal of Cs⁺, Sr²⁺, and Eu³⁺ ions is achieved by two metal sulfides (FJSM-SnS-2 and FJSM-SnS-3). Both structures feature [Sn₃S₇]_n^2n- layers with the mixed cations of [CH₃NH₃]⁺ and [Bmmim]⁺ (1-butyl-2,3-dimethylimidazolium) as templates. However, the ratios and arrangements of mixed cations in the interlayered spaces are distinct. It is unprecedented that [CH₃NH₃]⁺ and [Bmmim]⁺ in FJSM-SnS-2 are alternatingly arranged in different interlayered spaces, whereas they in FJSM-SnS-3 are located in the same interlayered spaces. It is the first time that the ionic liquid cation and protonated organic amine have been simultaneously incorporated into metal sulfides. Both compounds show high capacities, rapid kinetics, and a wide pH active range for Cs⁺, Sr²⁺, and Eu³⁺. Even under excess Na⁺ ions, both show excellent selectivity in capturing trace Sr²⁺ and Eu³⁺ ions. FJSM-SnS-3 presents the highest K_d^Eu to date. They still retain high removal efficiency even after intense β and γ radiation. Moreover, it is first confirmed by the in situ tracking method of mass spectrometry that the large-sized [Bmmim]⁺ ions are exchangeable. It is found that the arrangement of cations between interlayered spaces is a crucial factor affecting ion exchange performance. This work will likely change the consensus that large-sized organic cations are difficult to be exchanged and thus further highlight the great potential of metal sulfide ion exchangers for radionuclide remediation.