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 three Nb-POM clusters were isolated and structurally characterized; [Nb14O40(O-2)(2)H-3](14-), [((UO2)(H2O))(3)Nb-46(UO2)(2)O136H8(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 counter-cations (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 burgeoning Nb-POM family, it now transects all major metal groups of the periodic table.