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Efficient Cs + -Sr 2+ separation, highly desirable for radionuclide recovery in medical and industrial applications, was achieved by the ion exchange technique over a novel microporous silver selenidostannate, [NH 3 CH 3 ] 0.5 [NH 2 (CH 3 ) 2 ] 0.25 Ag 1.25 SnSe 3 ( AgSnSe-1 ). This material was synthesized in deep eutectic solvent (DES), where the alkylammonium cations play significant structure-directing roles in the construction of micropores that allow for selective ion exchange toward Cs + against Sr 2+ . The much greater K d Cs (1.06 × 10 4 mL g -1 ) over K d Sr (87.7 mL g -1 ) contributes to an outstanding separation factor SF Cs/Sr of ∼121.4 that is top-ranked among inorganic materials. An ion exchange column filled with AgSnSe-1 exhibits a remarkable separation effect for 10 000 bed volumes of continuous flow, with removal rates of ∼99.9% and ∼0 ± 5.5% for Cs + and Sr 2+ , respectively. AgSnSe-1 exhibits excellent β and γ radiation resistances and a chemical stability over a broad pH range of 1-12. The Se leaching level below the safe guideline value for drinking water highlights the environmental-friendly nature of AgSnSe-1 . The high Cs + exchange performance is almost unaffected by Na + , Mg 2+ , and Ca 2+ cations. The Cs + -laden product AgSnSe-1Cs can be facilely eluted for recycling use, highlighting the great potential of open framework metal selenides in nuclear waste treatment and renewable energy utilization.

Rational synthesis of inorganic matter remains a great challenge encountered with modern synthetic chemistry. Here we reported the stepwise solvothermal conversion from GeO 2 to [MGe 4 S 10 ] n 3 n - (M = Cu, Ag) polymer via isolatable [Ge 2 S 6 ] 4- and [Ge 4 S 10 ] 4- anions by virtue of templating technique. The facile sulfuration of GeO 2 resulted in the methylammonium-templated dimeric thiogermanate [CH 3 NH 3 ] 4 Ge 2 S 6 ( 1 ). This was used subsequently as a precursor for the formation of adamantane-like [Ge 4 S 10 ] 4- cluster, which was isolated as a mixed methylammonium/ethylammonium salt [CH 3 CH 2 NH 3 ] 3 [CH 3 NH 3 ]Ge 4 S 10 ( 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 [(CH 3 CH 2 ) 4 N] 3 MGe 4 S 10 (M = Cu ( 3 ), Ag ( 4 )), whose anionic moieties feature a novel zigzag chainlike structure constructed by [Ge 4 S 10 ] 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.