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Coordination Chemistry: Optical Isomers

Two isomers of Fe(bpy)32+ are shown in the boxes below. The abbreviation bpy stands for 2,2'-bipyridine. The bpy ligand is a bidentate ligand that coordinates through the two aromatic nitrogens. As you examine the structures of the two isomers, note that the bonding is identical in both isomers. In fact, the two isomers have identical physical properties and chemical reactivity ... except in circumstances where the reaction environment is chiral.

You will notice that the two isomers are mirror images of each other. Select the "Mirror Images" button to orient the molecules to clearly illustrate this property. Chiral molecules are molecules that cannot be superimposed upon their mirror image. Such molecules exist in two isomeric forms called enantiomers.

  1. Verify that the two isomers of Fe(bpy)32+ are mirror images.
  2. Chiral molecules either have no symmetry elements or only an axis of proper rotation. In this example, the isomers have a three-fold or C3 axis of symmetry. See if you can locate this axis. When one performs a one-third rotation about this axis, the molecule will look identical to its original appearance. Click on the "View Along Three-Fold Axis" to view each molecule looking down the axis of symmetry.
  3. Click on "View Along Three-Fold Axis" and carefully examine each isomer. You should see a propeller-like structure; this may be easiest to see with the space-filling format. One propeller turns to the left (the Λ isomer) and the other propeller turns to the right (the Δ isomer). The word chiral derives from the Greek word cheir, which means "hand". Chiral molecules are left-handed or right-handed.
Λ-tris(2,2'-bipyridine)iron(II) ion Δ-tris(2,2'-bipyridine)iron(II) ion



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Coordination Chemistry Isomers

Coordination Isomers       Linkage Isomers       Geometric Isomers       Optical Isomers

Isomerization Summary

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