Understanding isomerization in octahedral complexes can be challenging for students in inorganic chemistry. Grasping concepts relating to molecular geometry and structure, especially with octahedral complexes is difficult. This becomes particularly apparent when discussing chirality in octahedral complexes. In order to understand chirality, the uniqueness (or handedness) between mirror image objects obtained from failure to superimpose one upon the other, one must be able to visualize objects in three dimensions. In organic chemistry, a chiral molecule is taught using the concept of an asymmetric carbon center, called the chiral carbon, which is bonded to four different groups or atoms. This gets more complicated in inorganic chemistry where the chiral center is the metal in an octahedral complex. The configurations of enantiomeric octahedral tris(bidentate ligand) metal complexes are designated lambda and delta, based on the direction of the helix formed by the chelating ligands. To study this distinction, a computational study was designed to prove chirality in octahedral complexes. The molecule chosen for this activity is the tris(bipyridine)ruthenium(II) ion. The activity starts with students drawing the molecule in a 3D structure drawing program and then drawing the mirror image in a second window placed side-by-side with the first. In order to confirm the visual inspection, students then compute circular dichroism spectra for the molecule. Chiral molecules uniquely interact with polarized light due to the dissymmetry in their molecular orbitals. Vibrational Circular Dichroism (VCD) and Electronic Circular Dichroism (ECD) are absorbance events of circularly polarized light exhibited by chiral molecules. Therefore, determining if a molecule is chiral may be achieved by computing its CD spectra: where a peaked spectrum is produced by chiral molecules and a zero-intensity flat-lined spectrum is obtained for achiral molecules. Additionally, enantiomers give mirror image CD spectra. A description of this activity, including visuals and CD spectra will be presented.

Computational activity to visualize stereoisomers in octahedral tris(bidentate ligand) transition metal complexes

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