Prior to a study of the (relative) stability of larger clusters, we validated the calculation of the free energies using TB methods, based on the DFT values already calculated as benchmarks. Figure represents the formation energies of all the clusters studied in the previous sections (with Im -and mIm -ligands) calculated with the DFT ωB97X method and the semiempirical GFN2-xTB method. We find a good correlation between the two levels of theory, which will allow us to perform GFN2-xTB/ALPB(ethanol) calculations to study larger clusters, with an accuracy that is very similar to that of the much more time consuming ωB97X/6- Figure : Geometries and energies (in eV, in parenthesis) of some relevant large clusters, with a number of Zn 2+ cations ranging from 5 to 144. The number of Zn 2+ cations and Im -ligands are shown using the (z, l) notation. The energy is calculated from the linear regression reported in Figure . Color code as in Figure .