Relativistic effects in the gas-phase molecular hydration of heavy atomic transition metal cations (Groups 10–12): Group variations in energetics and kinetics

We assess relativistic effects in the molecular hydration of late atomic transition metal cations (Groups 10–12) as revealed by a review of previously published experimental and theoretical hydration energies and by kinetic measurements at room temperature. To fill gaps in theoretical hydration energies, we report here newly computed hydration energies, with and without relativistic effects, for all 9 atomic transition metal ions in the three Groups using DFT and RI-MP2 theory. Rate coefficients are taken from previous work in our laboratory and we provide here, for the first time, the raw experimental data for the kinetics of all 9 hydration reactions. Trends in hydration energies and hydration kinetics are inspected and compared going down the Periodic Table. We find a strong 3rd-row enhancements in the hydration energy and the rate of hydration and these are attributed to relativistic contributions to the bonding of H₂O to the 3rd-row transition metal cations. This behaviour is very much in line with that reported earlier with other molecular ligands.