Pentaamminenitritocobalt(III) chloride explained

Pentaamminenitritocobalt(III) chloride is an inorganic compound with the molecular formula [Co(NH₃)₅(NO₂)]Cl₂. It is an orange solid that is soluble in water. Although it has no applications, the compound has been of academic interest as a source of the transition metal nitrite complex [Co(NH₃)₅(NO₂)]²⁺.

Linkage isomers

The coordination complexes [Co(NH₃)₅(NO₂)]²⁺ and [Co(NH₃)₅(ONO)]²⁺ provided an early example of linkage isomerism. This nitritopentaamminecobalt(III) isomer converts to the more stable nitro form at room temperature.^[1] 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.^[2] 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.^[3] The O-linkage isomer scrambles rapidly between the two oxygen sites, i.e. Co-O*NO/Co-ONO*.^[4]

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.^[5] 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.

Notes and References

1. Hohman, W. H. . A Combined Infrared and Kinetic Study of Linkage Isomers. An Inorganic Experiment . Journal of Chemical Education. 51. 1974. 553. 10.1021/ed051p553. 8. 1974JChEd..51..553H .
2. Brasted, R. . Hirayama, C. . An Examination of the Absorption Spectra of Some Cobalt(III)-Amine Complexes. Effect of Ligand and Solvents in Absorption . J. Phys. Chem.. 63. 1959. 780–6. 10.1021/j150576a003. 6.
3. Penland, R. . Lane, T. . Quagliano, J. . Infrared Absorption Spectra of Inorganic Coordination Complexes. VII. Structural Isomerism of Nitro- and Nitritopentaamminecobalt(III) Chlorides . Journal of the American Chemical Society. 78. 1956. 887–9. 10.1021/ja01586a001. 5.
4. 10.1016/S0020-1693(00)90574-7. Oxygen scrambling in pentaamminenitritocobalt(III) revisited. 1988. Jackson. W.G.. Inorganica Chimica Acta. 149. 101–104.
5. Crawford, B. . Talburt, D. . Johnson, D. . Effects of Cobalt(III) Complexes on Growth and Metabolism of Escherichia coli. Bioinorganic Chemistry. 3. 1974. 121–33. 10.1016/S0006-3061(00)80035-6. 2. 4613388 .