Pentaamminenitritocobalt(III) chloride

Linkage isomers

The coordination complexes [Co(NH3)5(NO2)]2+ and [Co(NH3)5(ONO)]2+ were the first observed case of linkage isomerism. This nitritopentaamminecobalt(III) isomer converts to the more stable nitro form at room temperature. The two isomers can be distinguished by UV-Vis spectroscopy. Absorbance maxima for the nitro isomer occur at 457.5, 325, and 239 nm. The nitrito has maxima at 486, 330, and 220 nm. Their IR spectra also differ. The nitrito isomer absorbs at 1460 and 1065 cm−1. The nitro isomer absorbs at 1430 and 825 cm−1. The O-linkage isomer scrambles rapidly between the two oxygen sites, i.e. Co-ONO/Co-ONO.

In the related chloronitrate salt, the linkage isomerism causes thermosalience.

Preparation and reactions

Nitritopentaamminecobalt(III) chloride is prepared by treating chloropentamminecobalt chloride with sodium nitrite: :[Co(NH3)5Cl]2+ + NO2− → [Co(NH3)5(ONO)]2+ + Cl− Heating a solution of the nitrito complex gives the nitro isomer.

Nitropentaamminecobalt(III) chloride has been studied for its ability to repress cell division. This property has been tested to inhibit the growth of tumors and bacteria such as E. coli. However, it has been found that several other compounds are superior inhibitors.

References

References

1. (1979). "Nitrito-Nitro Linkage Isomerization in the Solid State. 2. A Comparative Study of the Structures of Nitrito- and Nitropentaamminecobalt( 111) Dichloride". [[Inorganic Chemistry (journal).
2. Hohman, W. H.. (1974). "A Combined Infrared and Kinetic Study of Linkage Isomers. An Inorganic Experiment". [[Journal of Chemical Education]].
3. (1959). "An Examination of the Absorption Spectra of Some Cobalt(III)-Amine Complexes. Effect of Ligand and Solvents in Absorption". [[J. Phys. Chem.]].
4. (1956). "Infrared Absorption Spectra of Inorganic Coordination Complexes. VII. Structural Isomerism of Nitro- and Nitritopentaamminecobalt(III) Chlorides". [[Journal of the American Chemical Society]].
5. (1988). "Oxygen scrambling in pentaamminenitritocobalt(III) revisited". Inorganica Chimica Acta.
6. (2013). "Dynamic Single Crystals: Kinematic Analysis of Photoinduced Crystal Jumping (The Photosalient Effect)". Wiley.
7. (1974). "Effects of Cobalt(III) Complexes on Growth and Metabolism of Escherichia coli". [[Bioinorganic Chemistry]].