© 2017 Elsevier Inc. To understand the corrosion of bulk oxide materials at the molecular scale, oxygen–isotope exchanges were examined in two classes of nanometer-sized ions, one cation and one anion, and subsets that differ by targeted single-atom substitutions. In niobate anions, the different oxygen sites within each molecule differ by ∼ 103–104 in overall rates of isotopic exchange, yet all structural oxygens exhibit similar pH dependencies that relate to the dissociation pathways. In aluminate cations of the ɛ-Keggin structure, single-atom substitutions cause a 107–1010 variation of rates of oxygen–isotopic exchange into two sets of μ2-OH. Molecular-dynamic simulations indicate that metastable forms of these structures exist as loose, long-lived intermediates. A series of common steps is observed to access the intermediate structures, and these are best resolved in the symmetric ɛ-Keggin aluminate ions. In the first step, solvation forces, or a nucleophile, cause a near-surface metal to partly detach from a deeper overbonded oxygen via concerted motions of many atoms. Isotopically distinct oxygens then add to the newly undercoordinated metal in the partly detached metastable state. Protons transfer to more basic oxygens and oxygens shuffle. Finally, the metastable structure collapses and dehydrates. The number of such metastable states depends on the symmetry and composition of the starting structure and access to the metastable state controls the overall rates. Surprisingly, polyoxometalate ions with only 40–100 atoms already seem to capture much of the macroscopic chemistry observed for dissolving minerals and glasses.