Difference between revisions of "Linkage isomerism"
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Latest revision as of 19:18, 21 September 2010
Linkage isomerism is the existence of co-ordination compounds that have the same composition differing with the connectivity of the metal to a ligand.
Typical ligands that give rise to linkage isomers are:
- thiocyanate, SCN-
- selenocyanate, SeCN-
- nitrite, NO2-
- sulfite, SO32-
Examples of linkage isomers are violet-colored [(NH3)5Co-SCN]2+ and orange-colored [(NH3)5Co-NCS]2+. The isomerization of the S-bonded isomer to the N-bonded isomer occurs intramolecularly.[1] In the complex, dichlorotetrakis(dimethyl sulfoxide)ruthenium(II), linkage isomerism of dimethyl sulfoxide ligands can be observed in the NMR spectrum due to the effect of S vs. O bonding on the methyl groups of DMSO.
History
The first reported example of linkage isomerism had the formula [Co(NH3)5(NO2)]Cl2. The cationic cobalt complex exists in two separable linkage isomers. In the yellow-coloured isomer, the nitro ligand is bound through nitrogen. In the red linkage isomer, the nitrito is bound through one oxygen atom. The O-bonded isomer is often written as [Co(NH3)5(ONO)]2+. Although the existence of the isomers had been known since the late 1800’s, only in 1907 was the structural difference explained.[2] It was later shown that the red isomer converted to the yellow isomer upon UV-irradiation. In this particular example, the formation of the nitro isomer (Co-NO2) from the nitrito isomer (Co-ONO) occurs through the rearrangement of the molecular structure. Thus, no bonds are broken during isomerization.
References
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<references />, or <references group="..." />- ↑ Buckingham, D. A.; Creaser, I. I.; Sargeson, A. M. (1970). "Mechanism of Base Hydrolysis for CoIII(NH3)5X2+ Ions. Hydrolysis and Rearrangement for the Sulfur-Bonded Co(NH3)5SCN2+ Ion". Inorg. Chem. 9: 655–661. doi:10.1021/ic50085a044.<
- ↑ Werner, A. (1907). "Über strukturisomere Salze der Rhodanwasserstoffsäure und der salpetrigen Säure". Ber. 40: 765–788. doi:10.1002/cber.190704001117.
