To better visualize the similarities among the extracted metal-chelating groups, a hierarchical tree based on substructure relationships of the extracted metal-chelating groups was constructed. First, all generated metal-chelating groups were used as input for substructure searches in all groups and the matches were recorded, except of matches between identical groups or if the matched groups had the same number of heavy atoms and same standard InChI string. In the next step, metal-chelating groups which were not contained in any other metal-chelating group as substructure were assigned as roots of the tree. Subsequently, out of all substructures represented in one root, the node was identified as the substructure that was not contained in any other metal-chelating group except the node above it. This process was repeated until the leaf node was reached.