Pentaamminenitritocobalt(III) chloride

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. The compound has been of academic interest as a source of the transition metal nitrite complex [Co(NH₃)₅(NO₂)]²⁺.

Pentaamminenitritocobalt(III) chloride

Identifiers
CAS Number	13782-02-0
3D model (JSmol)	Interactive image
PubChem CID	414190
InChI InChI=1S/2ClH.Co.NO2.5H3N/c;;;2-1-3;;;;;/h2*1H;;;5*1H3/q;;+2;;;;;;/p-2 Key: XDIZJFSXOMJOOS-UHFFFAOYSA-L
SMILES [Cl-].[Cl-].O=N(=O)[Co+2]([NH3])([NH3])([NH3])([NH3])[NH3]
Properties
Chemical formula	H15N6O2Cl2Co
Molar mass	261.00 g/mol
Density	1.83 g/mL[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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.^[2] 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.^[3] 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.^[4] The O-linkage isomer scrambles rapidly between the two oxygen sites, i.e. Co-O*NO/Co-ONO*.^[5]

In the related chloronitrate salt, the linkage isomerism causes thermosalience.^[6]

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.^[7] 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.