Template Tool#

The template tool makes it easy to build up molecules from pre-defined ligands or functional groups, for example metal complexes or organometallic species.

Template tool window indicating menus for element, formal charge, and coordination geometry

Inserting Atoms with Specific Geometry#

The “Element” menu includes many common transition metals as well as carbon, phosphorous and sulfur, as well as “Other…” which brings up a periodic table to select any element.

Menu of elements, including carbon, phosphorus, sulfur, and transition metals

The “Formal Charge” menu allows you to specify a formal charge on the atom, which is used to calculate the total molecular charge for a calculation or force field optimization.

The “Coordination” menu allows you to specify the number of attachment points and geometry of the atom, including common arrangements from one to eight ligands. This includes linear, trigonal planar, tetrahedral, square planar, trigonal bipyramidal, octahedral, as well as less common geometries such as square pyramidal, trigonal prism, pentagonal bipyramidal, and square antiprism.

Menu of coordination geometries including linear, trigonal planar, tetrahedral, square planar, trigonal bipyramidal, and octahedral

After selecting a coordination type from the menu, the preview will update to reflect the geometry.

Once you have selected the element, formal charge (if desired), and coordination, click in the scene to insert the atom.

Image of octahedral iron atom with six white hydrogen atoms

Attaching Ligands#

The second tab in the template tool window allows you to select from a range of ligand types, including common bidentate, tridentate, tetradentate, and hexadentate ligands as well as conjugated haptic ligands.

Dialog of ligand types in Avogadro

After you change the type of ligand, the list of ligands will change accordingly. Similarly, after chosing a particular ligand, the preview image will update.

For monodentate or haptic ligands, click on a hydrogen atom to attach the new ligand.

Example of ammine ligand attached to an octahedral iron atom

For bidentate, tridentate, tetradentate, and hexadentate ligands, click on multiple hydrogen atoms and the ligand will be attached accordingly. For example for a tridentate ligand, click on three atoms in order. If you click on three sites in a line, but the tridentate ligand is a triangle, Avogadro will attach a “best fit.”

Iron bipyridine molecule

Attaching Functional Groups#

Functional groups are similar to monodentate ligands in that they attach to a molecule through one new bond.

Beyond the common choices, “Other…” includes a library of over 100 functional groups organized by element, e.g., sulfonates, acid anhydrides, boronic acids, etc.

Selecting other functional groups in a dialog organized by element

After selecting a group, a preview will appear. Click the “Insert” button and click on a hydrogen atom in the scene to attach the fragment of your choice.

Creating New Ligands#

While the ligand library includes many common ligands, you may wish to create your own or tweak a ligand before attachment.

As an example, we will build the salen ligand and add the attachment point for this tetradentate ligand. The process is similar for other ligands – Avogadro will use the location of a dummy atom (element zero) to determine where to attach to a metal or molecule.

After creating your ligand molecule, you should select the atoms which will be the attachement sites:

salen molecule with four selected atoms: two oxygen and two nitrogen

The Build ⇒ Add Centroid command will add a dummy atom at the center of the selected atoms:

menu indicating "Add Centroid" command

The ligand will now have a centroid dummy atom added. Draw bonds as desired to the attachment sites.

salen ligand with four selected atoms and new centroid dummy atom

The ligand can either be copied to the clipboard to insert via the Clipboard ligand type, or saved as CJSON to contribute to the fragment repository

Creating New Haptic Ligands#

Haptic ligands indicate bonding between a metal center and a delocalized pi system, such as an aromatic ligand.

As an example, we will build up an η4-cyclooctatetraene ligand. Either draw the molecule or use File ⇒ Import ⇒ Download by Name… to insert the basic molecule.

cyclooctatetraene molecule

Now select the four atoms to use for the haptic ligand:

cyclooctatetraene molecule indicating four selected carbon atoms

Now use the “Add Centroid” command to add a dummy atom at the centroid of the selected atoms. This is useful to create distinct hapticity (e.g., η3 cyclopentadienyl after selecting three carbon atoms instead of five):

cyclooctatetraene molecule indicating four selected carbon atoms and dummy attachment point

For a haptic ligand, we need one more dummy atom, perpendicular to the pi system. We can add an additional dummy atom perpendicular to the centroid:

Menu indicating "Add Perpendicular" item for haptic attachment points

After adding the perpendicular attachment, draw a bond between the centroid and the attachment site.

You can either save this file as CJSON to contribute to the repository, or “Select None” to deselect all atoms and copy the ligand to insert into a new molecule.