The PDB files were processed using Python scripts. First, a search for ligands containing heteroatoms ≤ 2.6 Å away from the metal ion (Mg 2+ , Mn 2+ or Zn 2+ ) was performed. Ligands that were metal ions or were classified as "unknown" by the PDB were disregarded (65 in total, see Supporting Information S2). For the remaining ligands, the coordinates for the chelating atoms were recorded and the ligand was extracted from the PDB file and save as a SD file using PyMOL. Next, out of the ligands retrieved, metal-chelating groups were extracted in the following way making use of the RDKit package (Scheme 1): A Monodentate ligands (1 chelating atom within 2.6 Å from the metal ion)