In order to use the bidentate ligands, we must start with a bare metal center.
Place an iron atom in the drawing area Select the Structures → Ligands → Bidentates → Ethylenediamine structure Double-click on the metal atom
You can see that, in this case, the metal atom is not replaced by an atom of the structure, contrary to previous experience, but that the bidentate ligand is simply attached to the central metal atom. This works because the 'replacing' atom in all bidentate structures is a dummy atom, which has the property that it won't replace an existing atom. The metal atom will simply take over the bonds that existed on the dummy atom in the structure. You can easily verify this when you would place the structure in empty space. Other multidentate ligands are defined in a similar fashion.
Press spacebar and double-click again on the metal atom
Notice that the second ligand appears opposite the existing one.
