Copper(II) glycinate (IUPAC suggested name: bis(glycinato)copper(II)) refers to 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 ...

of copper(II) with two equivalents of

glycinate 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 ( carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinogen ...

, with the formula u(glycinate)₂(H₂O)_''x''where ''x'' = 1 (''monohydrate'') or 0 (''anhydrous'' form). The complex was first reported in 1841, and its chemistry has been revisited many times, particularly in relation to the isomerisation reaction between the ''cis'' and ''trans'' forms which was first reported in 1890. All forms are blue solids, with varying degrees of water

solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

. A practical application of the compound is as a source of dietary copper in animal feeds.

Synthesis

Bis(glycinato)copper(II) is typically prepared from the reaction of

copper(II) acetate Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the formula Cu(OAc)2 where AcO− is acetate (). The hydrated derivative, Cu2(OAc)4(H2O)2, which contains one molecule of water for each copper atom, is availa ...

in aqueous ethanol with glycine: : Cu(OAc)₂ + 2 H₂NCH₂COOH + ''x'' H₂O → u(H₂NCH₂COO)₂(H₂O)_''x''+ 2 AcOH, ''x'' = 0 or 1 The reaction proceeds through a non-redox

dissociative substitution In chemistry, dissociative substitution describes a reaction pathway by which compounds interchange ligands. The term is typically applied to coordination and organometallic complexes, but resembles the SN1 mechanism in organic chemistry. T ...

mechanism and usually affords the ''cis'' isomer.

Structure

Like most amino acid complexes, the glycinate forms a 5-membered chelate ring, with the glycinato ligand serving as a bidentate (''κ''²''Ο,Ν'') species. The chelating ligands assume a square planar configuration around the copper atom as is common for tetracoordinate ''d''⁹ complexes, calculated to be much lower in energy than the alternative tetrahedral arrangement.

''Cis'' and ''trans'' isomerism

The unsymmetric nature of the ligand and square planar coordination thereof gives rise to two possible geometric isomers: a ''cis'' and a ''trans'' form. Multiple ways of differentiating the geometric isomers exist, an easily accessible one being

IR spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functio ...

with the characteristic number of C–N, C–O, and Cu^II–N identifying the ligand configuration. Crystal appearance may also be of some value for isomer indication, though the ultimate diagnostic technique is

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

.{{Cite journal, last1=Köse, first1=Dursun Ali, last2=Toprak, first2=Emre, last3=Kaşarcı, first3=Aliye, last4=Avcı, first4=Emre, last5=Avcı, first5=Gülçin Alp, last6=Şahin, first6=Onur, last7=Büyükgüngör, first7=Orhan, date=2016-07-02, title=Synthesis, Spectral, and Thermal Studies of Co(II), Ni(II), Cu(II), and Zn(II)-Glycinato Complexes and Investigation of Their Biological Properties: Crystal Structure of u(µ-gly) 2 (H 2 O)n, url=https://www.tandfonline.com/doi/full/10.1080/15533174.2013.801855, journal=Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, language=en, volume=46, issue=7, pages=1109–1118, doi=10.1080/15533174.2013.801855, s2cid=101548954 , issn=1553-3174 All forms of the complex have been characterized crystallographically, the most commonly isolated one being the ''cis'' monohydrate (''x'' = 1). Isomerisation of the ''cis'' to the ''trans'' form occurs at high temperatures ''via'' a ring-twisting mechanism.

References

Coordination chemistry Copper complexes Glycinates