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; [Nb14 O40 (O2 )2 H3 ]14- , [((UO2 )(H2 O))3 Nb46 (UO2 )2 O136 H8 (H2 O)4 ]24- , and [(Nb7 O22 H2 )4 (UO2 )7 (H2 O)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 UO2 2+ moieties) are stabilized by replacing labile H2 O/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.