Predefined Metal Complex Geometries

Select the 'ML6 Octahedral' from the metal complex structures and place it in the drawing area 

Notice that six dummy ("Xx") atoms have been placed around the metal center in an octahedral fashion.

Select all the dummy atoms by right-clicking (or click and hold down) to get the atom popup
Select Atom Popup → 'Select all Xx

The Ligands structure submenu contains a number of ligands which can be used to replace the dummy atoms. The Structure menu can, however, also be reached via the atom pop-up menu.

Right-click on one of the selected dummy atoms
Select the Atom Popup → Ligand → CN structure

Notice that all dummy atoms in the selection are replaced by CN ligands.