Chloropentamminecobalt chloride is the dichloride salt of the
coordination complex
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...
o(NH3)5Clsup>2+. It is a red-violet, diamagnetic, water-soluble salt. The compound has been of academic and historical interest.
Synthesis and reactions
The salt is prepared with a two-step process starting with oxidizing a solution of cobalt chloride and ammonia.
:2 CoCl
2·6H
2O + 10 NH
3 + 2 HCl + H
2O
2 → 2
o(NH3)5(OH2)l
3 + 12 H
2O
This intermediate is then heated to induce coordination of one of the outer sphere chloride ligands:
:
o(NH3)5(OH2)l
3 →
o(NH3)5Cll
2 + H
2O
The dication
o(NH3)5Clsup>2+ has idealized C
4v symmetry
Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...
.
In an aqueous solution, chloropentaamminecobalt(III) chloride reforms aquopentammine complex. With concentrated
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
, chloropentaamminecobalt(III) chloride forms the hydrogen sulfate complex
o(NH3)5OSO3Hsup>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
Alfred Werner (12 December 1866 – 15 November 1919) was a Swiss chemist who was a student at ETH Zurich and a professor at the University of Zurich. He won the Nobel Prize in Chemistry in 1913 for proposing the octahedral configuration of ...
was awarded the
Nobel Prize in Chemistry
)
, image = Nobel Prize.png
, alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then "M ...
. Prior to Werner, the models of amine complexes postulated chains of pentavalent nitrogen centers. This
Jørgensen
Jorgensen or Joergensen (original spelling: Jørgensen ) is a common Danish-Norwegian patronymic surname meaning "son of Jørgen" (Danish version of the Greek Γεώργιος (geōrgios), cf. English George). Jørgensen is the tenth most common ...
–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.
In
o(NH3)5Cll
2, 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
*
Pentaamminechlororhodium dichloride
Pentamminechlororhodium dichloride is the dichloride salt of the coordination complex . It is a yellow, water-soluble solid. The salt is an intermediate in the purification of rhodium from its ores.
As shown by X-ray crystallography, the salt co ...
References
{{Reflist
Cobalt complexes
Cobalt(III) compounds
Ammine complexes