Chloropentamminecobalt chloride

Chloropentamminecobalt chloride is the dichloride salt of the coordination complex [Co(NH3)5Cl]2+. It is a red-violet, diamagnetic, water-soluble salt. The compound has been of academic and historical interest.

Chloropentaamminecobalt(III) chloride
Names
IUPAC name
Pentaamminechlorocobalt(III) chloride
Other names
Pentaamminechlorocobalt(III) chloride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.034.163
EC Number
  • 237-594-8
Properties
[Co(NH3)5Cl]Cl2
Molar mass 250.4 g/mol
Appearance red-violet rhomb-shaped crystal
Density 1.783 g/mL
Boiling point N/A
0.4 g/100 mL
Vapor pressure 5990 mm Hg
Thermochemistry
Std enthalpy of
formation (ΔfH⦵298)
 −1.0376E+06 Jmol−1; Molar Gibbs energy of formation = −606480 J/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Synthesis and reactions

The salt is prepared with a two-step process starting with oxidizing a solution of cobalt chloride and ammonia.[1][2]

2 CoCl2·6H2O + 10 NH3 + 2 HCl + H2O2 → 2 [Co(NH3)5(OH2)]Cl3 + 12 H2O

This intermediate is then heated to induce coordination of one of the outer sphere chloride ligands:

[Co(NH3)5(OH2)]Cl3 → [Co(NH3)5Cl]Cl2 + H2O

The dication [Co(NH3)5Cl]2+ has idealized C4v symmetry.[3] [4]

In an aqueous solution, chloropentaamminecobalt(III) chloride reforms aquopentammine complex. With concentrated sulfuric acid, chloropentaamminecobalt(III) chloride forms the hydrogen sulfate complex [Co(NH3)5OSO3H]2+.

History

Cobalt complexes have been of long-standing interest in inorganic chemistry because they are numerous, easily prepared, and colorful. It was partly on the basis of his study of cobalt coordination chemistry that Alfred Werner was awarded the Nobel Prize in Chemistry. Prior to Werner, the models of amine complexes postulated chains of pentavalent nitrogen centers. This Jørgensen–Bloomstrand model was overthrown by Werner who introduced the idea that coordination complexes feature metal atoms of octahedral and tetrahedral shapes, with ammonia and other ligands attached individually to the metal. Werner's model accounted for the inner sphere ligands being less reactive.[5] In [Co(NH3)5Cl]Cl2, two chloride ions are outer sphere (counter ions) and one is bound to the Co(III) center: reaction with excess silver nitrate would immediately precipitate the two chloride counter ions, but the bound chloride ion would not be precipitated.

See also

References
  1. Gert G. Schlessinger (1967). "Chloropentaamminecobalt(III) Chloride". Inorganic Syntheses. 9: 160. doi:10.1002/9780470132401.ch43.
  2. Williams, Gregory M; Olmsted, John, III; Preksa, Andrew P., III (1989). "Coordination complexes of cobalt: inorganic synthesis in the general chemistry laboratory". Journal of Chemical Education. 66: 1043–5. doi:10.1021/ed066p1043.CS1 maint: multiple names: authors list (link)
  3. G. G. Messmer; E. L. Amma (1968). "Redetermination of the crystal structure of chloropentaamminecobalt(III) dichloride". Acta Crystallogr. B. 24: 417–422. doi:10.1107/S0567740868002475.
  4. Hambley, Trevor W.; Lay, Peter A. (1986). "Comparisons of π-bonding and hydrogen bonding in isomorphous compounds: [M(NH3)5Cl]Cl2 (M = Cr, Co, Rh, Ir, Ru, Os)". Inorganic Chemistry. 25: 4553–8. doi:10.1021/ic00245a020.
  5. Schwab, E. (8 September 2003). "Cobalt". Chemical & Engineering News. 81 (36): 80. doi:10.1021/cen-v081n036.p080.
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