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 approximately 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.