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Tris(ethylenediamine)cobalt(III) chloride
Encyclopedia
Triscobalt(III) chloride is a coordination complex with the formula [Co(en)3]Cl3 (where "en" is the abbreviation for ethylenediamine). This complex was important in the history of coordination chemistry because of its stability and its stereochemistry
. Many different salts have been described. The complex was first described by Alfred Werner
who isolated this salt as yellow-gold needle-like crystals.
. The solution is purged with air to oxidize the cobalt(II)-ethylenediamine complexes to cobalt(III). The reaction proceeds in 95% yield, and the trication can be isolated with a variety of anions. A detailed product analysis of a large-scale synthesis revealed that one minor by-product was [Co(en)2Cl(H2NCH2CH2NH3]Cl3, which contains a rare monodentate ethylenediamine ligand (protonated).
The cation [Co(en)3]3+ is octahedral
with Co-N distances in the range 1.947-1.981 Å
. The N-Co-N angles are 85° within the chelate rings and 90° between nitrogen atoms on adjacent rings.
s that are described as Δ and Λ. Usually the resolution entails use of tartrate
salts. The optical resolution is a standard component of inorganic synthesis courses. Because of its nonplanarity, the MN2C2 rings can adopt either of two conformations
, which are described by the symbols λ and δ. The registry between these ring conformations and the absolute configuration of the metal centers is described by the nomenclature lel (when the en backbone lies parallel with the C3 symmetry axis) or ob (when the en backbone is obverse to this same C3 axis). Thus, the following diastereomer
ic conformations can be identified: Δ-(lel)3, Δ-(lel)2(ob), Δ-(lel)(ob)2, and Δ-(ob)3. The mirror images of these species of course exist also.
and alkyl amines typically crystallize with water in the lattice
, and the stoichiometry can depend on the conditions of crystallization and, in the cases of chiral complexes, the optical purity of the cation. Racemic [Co(en)3]Cl3 is most often obtained as the di- or trihydrate. For the optically pure salt (+)-[Co(en)3]Cl3.1.5H20, (+)-[Co(en)3]Cl3.0.5NaCl.3H2O, and (+)-[Co(en)3]Cl3.H2O are also known.
Stereochemistry
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms within molecules. An important branch of stereochemistry is the study of chiral molecules....
. Many different salts have been described. The complex was first described by Alfred Werner
Alfred Werner
Alfred Werner 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 transition metal complexes. Werner developed the basis for modern coordination chemistry...
who isolated this salt as yellow-gold needle-like crystals.
Synthesis and structure
The compound is prepared from an aqueous solution of ethylenediamine and virtually any cobalt(II) salt, such as cobalt(II) chlorideCobalt(II) chloride
Cobalt chloride is an inorganic compound of cobalt and chloride, with the formula CoCl2. It is usually supplied as the hexahydrate CoCl2·6H2O, which is one of the most commonly used cobalt compounds in the laboratory. The hexahydrate is deep purple in color, whereas the anhydrous form is sky blue...
. The solution is purged with air to oxidize the cobalt(II)-ethylenediamine complexes to cobalt(III). The reaction proceeds in 95% yield, and the trication can be isolated with a variety of anions. A detailed product analysis of a large-scale synthesis revealed that one minor by-product was [Co(en)2Cl(H2NCH2CH2NH3]Cl3, which contains a rare monodentate ethylenediamine ligand (protonated).
The cation [Co(en)3]3+ is octahedral
Octahedral molecular geometry
In chemistry, octahedral molecular geometry describes the shape of compounds where in six atoms or groups of atoms or ligands are symmetrically arranged around a central atom, defining the vertices of an octahedron...
with Co-N distances in the range 1.947-1.981 Å
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
. The N-Co-N angles are 85° within the chelate rings and 90° between nitrogen atoms on adjacent rings.
Stereochemistry
The complex can be resolved into enantiomerEnantiomer
In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are non-superposable , much as one's left and right hands are the same except for opposite orientation. It can be clearly understood if you try to place your hands one over the other without...
s that are described as Δ and Λ. Usually the resolution entails use of tartrate
Tartrate
A tartrate is a salt or ester of the organic compound tartaric acid, a dicarboxylic acid. Its formula is O−OC-CH-CH-COO− or C4H4O62−.As food additives, tartrates are used as antioxidants, acidity regulators, and emulsifiers...
salts. The optical resolution is a standard component of inorganic synthesis courses. Because of its nonplanarity, the MN2C2 rings can adopt either of two conformations
Chemical structure
A chemical structure includes molecular geometry, electronic structure and crystal structure of molecules. Molecular geometry refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. Molecular geometry can range from the very simple, such as...
, which are described by the symbols λ and δ. The registry between these ring conformations and the absolute configuration of the metal centers is described by the nomenclature lel (when the en backbone lies parallel with the C3 symmetry axis) or ob (when the en backbone is obverse to this same C3 axis). Thus, the following diastereomer
Diastereomer
Diastereomers are stereoisomers that are not enantiomers.Diastereomerism occurs when two or more stereoisomers of a compound have different configurations at one or more of the equivalent stereocenters and are not mirror images of each other.When two diastereoisomers differ from each other at...
ic conformations can be identified: Δ-(lel)3, Δ-(lel)2(ob), Δ-(lel)(ob)2, and Δ-(ob)3. The mirror images of these species of course exist also.
Hydrates
Cationic coordination complexes of ammoniaAmmonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
and alkyl amines typically crystallize with water in the lattice
Water of crystallization
In crystallography, water of crystallization or water of hydration or crystallization water is water that occurs in crystals. Water of crystallization is necessary for the maintenance of crystalline properties, but capable of being removed by sufficient heat...
, and the stoichiometry can depend on the conditions of crystallization and, in the cases of chiral complexes, the optical purity of the cation. Racemic [Co(en)3]Cl3 is most often obtained as the di- or trihydrate. For the optically pure salt (+)-[Co(en)3]Cl3.1.5H20, (+)-[Co(en)3]Cl3.0.5NaCl.3H2O, and (+)-[Co(en)3]Cl3.H2O are also known.