Cation adsorption and exchange has been an important topic in both basic and applied chemistry relevant to materials synthesis and chemical conversion, as well as purification and separation. Selective Cs(+) uptake from aqueous solutions is especially important because Cs(+) is expensive and is contained in radioactive wastes. However, the reported adsorbents incorporate Rb(+) as well as Cs(+) , and an adsorbent with high selectivity toward Cs(+) has not yet been reported. Highly selective uptake of Cs(+) by an ionic crystal (etpyH)2 [Cr3O(OOCH)6 (etpy)3]2 [α-SiMo12 O40 ]⋅3 H2O (etpy =4-ethylpyridine) is described. The compound incorporated up to 3.8 mol(Cs(+) ) mol(s)(-1) (where s=solid) by cation-exchange with etpyH(+) and reduction of silicododecamolybdate with ascorbic acid. The amount of Cs(+) uptake was comparable to that of Prussian blue, which is widely recognized as a good Cs(+) adsorbent. Moreover, other alkali-metal and alkaline-earth-metal cations were almost completely excluded (<0.2 mol mol(s)(-1)).

Cation adsorption and exchange has been an important topic in both basic and applied chemistry relevant to materials synthesis and chemical conversion, as well as purification and separation. Selective Cs+ uptake from aqueous solutions is especially important because Cs+ is expensive and is contained in radioactive wastes. However, the reported adsorbents incorporate Rb+ as well as Cs+, and an adsorbent with high selectivity toward Cs+ has not yet been reported. Highly selective uptake of Cs+ by an ionic crystal (etpyH)2[Cr3O(OOCH)6(etpy)3]2[α‐SiMo12O40]⋅3 H2O (etpy =4‐ethylpyridine) is described. The compound incorporated up to 3.8 mol(Cs+) mol(s)−1 (where s=solid) by cation‐exchange with etpyH+ and reduction of silicododecamolybdate with ascorbic acid. The amount of Cs+ uptake was comparable to that of Prussian blue, which is widely recognized as a good Cs+ adsorbent. Moreover, other alkali‐metal and alkaline‐earth‐metal cations were almost completely excluded (<0.2 mol mol(s)−1).

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