Tris(glycinato)cobalt(III) describes

coordination complex A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

es with the formula . Several isomers exist of these octahedral complexes formed between low-spin d⁶ Co(III) and the conjugate base of the amino acid

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...

Structures

Both a meridional isomer and a facial isomer are known. In the former the Co-O bonds share a plane, and in the facial isomer they do not. Each of these two isomers exists also as pairs of stereoisomers, termed Δ and Λ. This set of compounds are prototypes of many tris(aminocarboxylate) complexes, with the notable distinction that the Co(III) derivatives do not isomerize readily and can thus be separated. The violet isomer is obtained anhydrous, whereas the red derivative is the monohydrate. X-ray crystallographic characterization of the mer isomer demonstrates the existence of a dihydrate, however.

Synthesis

The reaction of glycine with

sodium tris(carbonato)cobalt(III) Sodium tris(carbonato)cobalt(III) is the inorganic compound with the formula Na3Co(CO3)3•3H2O. The salt contains an olive-green metastable cobalt(III) coordination complex. The salt, a homoleptic metal carbonato complex, is sometimes referred ...

produces both the violet meridional and red-pink facial isomers in approximately equal amounts. The compounds are separated by

fractional crystallization Fractional crystallization may refer to: * Fractional crystallization (chemistry), a process to separate different solutes from a solution * Fractional crystallization (geology) Fractional crystallization, or crystal fractionation, is one of the ...

. These complexes have been characterized by

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

.{{cite journal, journal=Acta Crystallogr, year=2007, volume=E63, pages=m740–m742, doi=10.1107/S1600536807005636, title=Tris(glycinato-κ²''N,O'')cobalt(III), first1=K.-Q., last1=Yu , first2=Y.-X. , last2=Sun , first3=R. , last3=Zhang , first4=N.-W. , last4=Zhang, first5=H.-W. , last5=Che The isomeric forms of tris(glycinato)cobalt(III) are poorly soluble in water. The solubility increases considerably in acidic solution.

References

Cobalt complexes Cobalt(III) compounds Octahedral compounds Glycinates