Calculation of Water-Exchange Rates on Aqueous Polynuclear Clusters and at Oxide−Water Interfaces

The rates of a wide variety of reactions in aqueous coordination compounds can be correlated with lifetimes of water molecules in the inner-coordination shell of the metal. For simple octahedral metal ions, these lifetimes span ∼1020 but are unknown, and experimentally inaccessible, for reactive sites in interfacial environments. Using recent data on nanometer-sized aqueous aluminum clusters, we show that lifetimes can be calculated from reactive-flux molecular dynamics simulations. Rates scale with the calculated metal−water bond lengths. Surprisingly, on all aluminum(III) mineral surface sites investigated, waters have lifetimes in the range of 10-8−10-10 s, making the surface sites as fast as the most reactive ions in the solution.