The effect of various FFs on the ligand exchange mechanism in Mg[(H 2 O) 6 ] 2+ complex was extensively studied by Schwierz et al., using transition path sampling. They demonstrated that while the commonly used non-polarizable FFs correctly predict the dissociative characteristics of the mechanism of the water exchange (I d ), they tend to overestimate the free energy barrier, leading to a significantly slower reaction rate. In comparison, the polarizable FF Amoeba and specialized non-polarizable FF microMg lead to a preference for an associative mechanism (I a ) with a reaction barrier too low, leading to significantly faster reaction rates, further illustrating the complexity of the ligand exchange process. The interactions of Pd 2+ with water molecules have also been studied computationally with classical FF approaches. Sanchez Marcos et al. investigated the [Pd(H 2 O) 4 ] 2+ complex in water using MD simulations. They developed two intermolecular potentials to describe the interactions between Pd 2+ and the water molecules, one for the first solvation shell, fitted to interaction energies computed at the MP2 level on the gas-phase complex, and another for the hydrated ion-bulk water interactions by incorporating a continuum polarizable model to account for solvation effects. They suggested the presence of solvent molecules in the axial position located between 2.5 and 3.0 Å, referred to as a 'mesoshell'. The concept of the mesoshell has sparked debate within the scientific community, with recent studies suggesting that the structure of Pd 2+ aqua complexes in water should be interpreted under the 'extended first shell' paradigm. For example, utilising QM/MM methods, Adnan Ali Shah et al. identified a weakly bound axial ligand (Pd-O distance of 2.8 Å), resulting in a broad peak in the RDF between the first and second solvation shells. Contrasting findings were reported by Chen et al. using subsystem DFT AIMD simulations of the same complex. Their results indicated that water molecules rarely occupied the axial region. Instead, solvent molecules formed a protective "dome" on both sides of the square planar complex via strong hydrogen bonds, preventing the penetration of single water molecules from the axial directions. These studies provide alternative interpretations of the experimental data, underscoring the complex nature of axial interactions in Pd 2+ aqua complexes.