Strategic capture of the {Nb7} polyoxometalate

Group V Nb‐polyoxometalate (Nb‐POM) chemistry generally lacks the elegant pH‐controlled speciation exhibited by Group VI (Mo,W) POM chemistry. Here we isolate and structurally characterize three Nb‐POM clusters; [Nb14O40(O2)2]14‐, [((UO2)(H2O))3Nb46(UO2)2O136H8(H2O)4]24‐, and [(Nb7O22H2)4(UO2)7(H2O)6]22‐, that effectively capture the aqueous Nb‐POM species from pH‐7 to pH‐10. These Nb‐POMs illustrate a reaction pathway for control over speciation that is driven by countercations (Li+) rather than pH. The two reported heterometallic POMs (with UO22+ moieties) are stabilized by replacing labile H2O/HO‐Nb=O with very stable O=U=O. The third isolated Nb‐POM features cis‐yl‐oxos, prior observed only in group VI POM chemistry. Moreover, with these actinide‐heterometal contributions to the burgeuoning Nb‐POM family, it now transects all major metal groups of the periodic table.