Bond stretch isomer

In chemistry, bond stretch isomerism is a concept of isomerism based on variations of bond length. The concept was proposed in the 1970's but was refuted in the 1990's.[1]

The phenomenon was first invoked to explain the observation of blue and green isomers of mer-MoOCl2(PMe2Ph)3, where PMe2Ph is dimethylphenylphosphine. These isomers were shown, purportedly, by X-ray crystallography to differ with respect to the length of the Mo-O bond, which differed by 0.2 Å. Subsequent work showed that the supposed green bond stretch isomer consisted of blue mer-MoOCl2(PMe2Ph)3 contaminated with a small amount of yellow mer-MoCl3(PMe2Ph)3. The nearly isomorphous replacement of Mo-O unit with small amounts of Mo-Cl unit results in artifactually long Mo-O distance in the green sample. Several such examples were uncovered. No example of bond stretch isomerism has been established.

References

  1. ↑ Parkin, G., "Bond-stretch isomerism in transition metal complexes: a reevaluation of crystallographic data", Chem. Rev. 1993, volume 93, 887-911. doi:10.1021/cr00019a003
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