Linkage isomerism 1766518 215956324 2008-05-30T12:56:49Z Puppy8800 5404759 iw '''Linkage isomerism''' is the existence of [[Complex (chemistry)|co-ordination compound]]s that have the same composition differing with the connectivity of the metal to a [[ligand]]. ==History== The first reported example of linkage isomerism had the formula [Co(NH<sub>3</sub>)<sub>5</sub>(NO<sub>2</sub>)]Cl<sub>2</sub>. The [[cation]]ic cobalt [[complex]] exists in two separable linkage isomers. In the red-coloured isomer, the nitro ligand is bound through nitrogen. In the yellow linkage isomer, the nitrito is bound through one oxygen atom. The O-bonded isomer is often written as [Co(NH<sub>3</sub>)<sub>5</sub>(ONO)]<sup>2+</sup>. Although the existence of the isomers had been known since the late 1800’s, only in 1907 was the structural difference explained.<ref> [[Alfred Werner|Werner]], A. “Über strukturisomere Salze der Rhodanwasserstoffsäure und der salpetrigen Säure” Berichte der deutschen chemischen Gesellschaft 1907, volume 40, 765-788. DOI: 10.1002/cber.190704001117</ref> 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-NO<sub>2</sub>) from the nitrito isomer (Co-ONO) occurs through the rearrangement of the molecular structure. Thus, no bonds are broken during isomerization. [[Image:LinkageIsomers.png|thumb|300px|center|Structures of the two linkage isomers of [Co(NH<sub>3</sub>)<sub>5</sub>(NO<sub>2</sub>)]<sup>2+</sup>.]] ==Scope of linkage isomerism== Typical ligands that give rise to linkage [[isomers]] are: *[[thiocyanate]], SCN<sup>-</sup> *[[selenocyanate]], SeCN<sup>-</sup> *[[nitrite]], NO<sub>2</sub><sup>-</sup> *[[sulfite]], SO<sub>3</sub><sup>2-</sup> Examples of linkage isomers are violet-colored [(NH<sub>3</sub>)<sub>5</sub>Co-SCN]<sup>2+</sup> and orange-colored [(NH<sub>3</sub>)<sub>5</sub>Co-NCS]<sup>2+</sup>. The isomerization of the S-bonded isomer to the N-bonded isomer occurs intramolecularly.<ref>Buckingham, D. A.; Creaser, I. I.; Sargeson, A. M. "Mechanism of Base Hydrolysis for Co<sup>III</sup>(NH<sub>3</sub>)<sub>5</sub>X<sup>2+</sup> Ions. Hydrolysis and Rearrangement for the Sulfur-Bonded Co(NH<sub>3</sub>)<sub>5</sub>SCN<sup>2+</sup> Ion" Inorganic Chemistry (1970), volume 9, pages 655-61.</ref> ==References== <references/> [[Category:Coordination chemistry]] [[Category:Chemical bonding]] {{chemistry-stub}} [[zh:键合异构]]