A redox-active inorganic crown ether based on a polyoxometalate capsule.

Cation-uptake has been long researched as an important topic in materials science. Herein we focus on a molecular crystal composed of a charge-neutral polyoxometalate (POM) capsule [Mo ^VI ₇₂ Fe ^III ₃₀ O ₂₅₂ (H ₂ O) ₁₀₂ (CH ₃ CO ₂ ) ₁₅ ] ³⁺ encapsulating a Keggin-type phosphododecamolybdate anion [α-PMo ^VI ₁₂ O ₄₀ ] ^3- . Cation-coupled electron-transfer reaction occurs by treating the molecular crystal in an aqueous solution containing CsCl and ascorbic acid as a reducing reagent. Specifically, multiple Cs ⁺ ions and electrons are captured in crown-ether-like pores {Mo ^VI ₃ Fe ^III ₃ O ₆ }, which exist on the surface of the POM capsule, and Mo atoms, respectively. The locations of Cs ⁺ ions and electrons are revealed by single-crystal X-ray diffraction and density functional theory studies. Highly selective Cs ⁺ ion uptake is observed from an aqueous solution containing various alkali metal ions. Cs ⁺ ions can be released from the crown-ether-like pores by the addition of aqueous chlorine as an oxidizing reagent. These results show that the POM capsule functions as an unprecedented "redox-active inorganic crown ether", clearly distinguished from the non-redox-active organic counterpart.
Competing Interests: There are no conflicts to declare.
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