The main conclusion we can draw from this analysis is that the presence of the explicit solvating molecule is key to obtaining an accurate profile along the reaction path. For instance, the profile calculated with the explicit ethanol molecule shows a local minimum, corresponding to the system in which the H atom from the OH group of the ethanol molecule has been transferred to one of the imidazolates of the ZnIm 3 E cluster, while the profile of the ZnIm 3 cluster, with no explicit ethanol, does not show any local minima. The energy barrier for the latter process is very small at 0.16 eV, compared to the 0.98 eV for the former), -i.e. an MD simulation in which no ethanol molecules (nor artificially added energy barriers to mimic them) were present, would not be able to realistically describe the transition states involved. On the other hand, we see that the presence of an explicit solvent molecule is not needed for achieving a good description of the equilibrium energies, since the energies of the initial and final states are correctly described using only implicit solvation. We have also studied the barrier when the solvating molecule is a NO - 3 counter anion, instead of an ethanol molecule. Due to the repulsive interaction between the Im -and NO - 3 moieties, the energy of the system easily reaches a value close to that of the transition state, ∼ 1.3 eV above the energy of the initial state when an ethanol molecule is included explicitly, and ∼ 1.0 eV when no explicit ethanol is present. However, the equilibrium energies for reactants and products are quite similar.