[Ln 6 O 8 ] Cluster‐Encapsulating Polyplumbites as New Polyoxometalate Members and Record Inorganic Anion‐Exchange Materials for ReO 4 − Sequestration

Various types of polyoxometalates (POMs) have been synthesized since the 19th century, but their assortment has been mostly limited to Groups 5 and 6 metals. Herein, a new family of POMs composed of a carbon group element as the addenda atoms with two distinct phases, LnPbOClO 4 ‐1 (Ln = Sm to Ho, Y) and LnPbOClO 4 ‐2 (Ln = Er and Tm) is reported. Both structures are built from [Ln 6 O 8 ] rare‐earth metal hexamers being incorporated in [Pb 18 O 32 ]/[Pb 12 O 24 ] polyplumbites, and unbound perchlorates as charge‐balancing anions. Impressively, YPbOClO 4 ‐1 and ErPbOClO 4 ‐2 exhibit exceptional uptake capacities (434.7 and 427.7 mg g −1 ) toward ReO 4 − , a chemical surrogate for the key radioactive fission product in the nuclear fuel cycle 99 TcO 4 − , which are the highest values among all inorganic anion‐exchange materials reported until now. The sorption mechanism is clearly elucidated and visualized by single‐crystal‐to‐single‐crystal structural transformation from ErPbOClO 4 ‐2 to a perrhenate‐containing complex ErPbOReO 4 , revealing a unique ReO 4 − uptake selectivity driven by specific interaction within Pb···O‐ReO 3 − bonds.