Tris(ethylenediamine)cobalt(III) chloride is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

with the formula o(en)₃l₃ (where "en" is the abbreviation for

ethylenediamine Ethylenediamine (abbreviated as en when a ligand) is the organic compound with the formula C2H4(NH2)2. This colorless liquid with an ammonia-like odor is a basic amine. It is a widely used building block in chemical synthesis, with approximately ...

). It is the chloride 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(en)₃sup>3+. This trication was important in the history of coordination chemistry because of its stability and its

stereochemistry Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereois ...

. Many different salts have been described. The complex was first described by

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 ...

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) chloride Cobalt(II) chloride is an inorganic compound of cobalt and chlorine, with the formula . The compound forms several hydrates ·''n'', for ''n'' = 1, 2, 6, and 9. Claims of the formation of tri- and tetrahydrates have not been confirmed.M. T. Sau ...

. 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 o(en)₂Cl(H₂NCH₂CH₂NH₃)l₃, which contains a rare monodentate ethylenediamine ligand (protonated). The cation o(en)₃sup>3+ is

octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...

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.

Stereochemistry

The point group of this complex is D₃. The complex can be resolved into

enantiomer In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...

s that are described as Δ and Λ. Usually the resolution entails use of

tartrate A tartrate is a salt or ester of the organic compound tartaric acid, a dicarboxylic acid. The formula of the tartrate dianion is O−OC-CH(OH)-CH(OH)-COO− or C4H4O62−. The main forms of tartrates used commercially are pure crystalline ta ...

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 In stereochemistry, diastereomers (sometimes called diastereoisomers) are a type of stereoisomer. Diastereomers are defined as non-mirror image, non-identical stereoisomers. Hence, they occur when two or more stereoisomers of a compound have dif ...

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.von Zelewsky, A. "Stereochemistry of Coordination Compounds" John Wiley: Chichester, 1995 .

Hydrates

Cationic coordination complexes of

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

and

alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloalk ...

amines typically crystallize with water in the

lattice Lattice may refer to: Arts and design * Latticework, an ornamental criss-crossed framework, an arrangement of crossing laths or other thin strips of material * Lattice (music), an organized grid model of pitch ratios * Lattice (pastry), an ornam ...

, and the stoichiometry can depend on the conditions of crystallization and, in the cases of chiral complexes, the optical purity of the cation. Racemic o(en)₃l₃ is most often obtained as the di- or trihydrate. For the optically pure salt (+)- o(en)₃l₃·1.5H₂O, (+)- o(en)₃l₃·0.5NaCl·3H₂O, and (+)- o(en)₃l₃·H₂O are also known.

References

{{reflist Cobalt complexes Cobalt(III) compounds Chlorides Metal halides Ethylenediamine complexes