Distortion
Definition and meaning of Distortion in chemistry.
Distortion, in chemistry, is a deviation of a molecule's or crystal's geometry from an ideal, symmetric shape, caused by electronic effects, steric strain, or lattice forces. It commonly appears in coordination compounds, where bond lengths or angles around a central atom become unequal instead of matching the idealized point group.
In more detail
Distortion often arises from the Jahn-Teller effect, in which unequal occupation of degenerate d-orbitals makes a perfectly symmetric arrangement of ligands energetically unstable, so the complex relaxes into a lower-symmetry geometry with reduced electronic energy. Distortion can also result from steric clashes between bulky ligands, crystal packing forces, or vibronic coupling in solids. Recognizing distortion is important because it explains anomalies in bond lengths, unexpected spectra and magnetic properties, and reduced symmetry in X-ray crystal structures.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Common cause | Jahn-Teller effect (electronic), steric strain, or crystal packing |
| Typical example | [Cu(H2O)6]2+ (Cu2+, d9) |
| Common result | Unequal bond lengths/angles, e.g., tetragonal elongation of an octahedron |
In the octahedral complex [Cu(H2O)6]2+, the copper(II) ion (d9 configuration) undergoes a Jahn-Teller distortion: the two axial Cu-O bonds stretch to about 238 pm while the four equatorial Cu-O bonds shorten to about 198 pm, converting a perfect octahedron into an elongated one.
Frequently asked questions
What is the Jahn-Teller theorem's connection to distortion?
The Jahn-Teller theorem states that any non-linear molecule in a degenerate electronic state will spontaneously distort to remove that degeneracy and lower its energy, which is why many octahedral d9 and high-spin d4 complexes are distorted rather than perfectly symmetric.
Is all molecular distortion electronic in origin?
No. Distortion can also be caused by steric repulsion between large ligands or substituents, or by external forces such as crystal lattice packing, independent of any electronic degeneracy.