Copper(II) glycinate

Copper(II) glycinate
	; Structure of the cis monohydrate form of bis(glycinato)copper(II)
Names
	IUPAC name bis(glycinato)copper(II)
	Other names cupric glycinate
Identifiers
CAS Number	13479-54-4 (anhydrous) ; 18253-80-0 (monohydrate) ;
3D model (JSmol)	Interactive image;
ChemSpider	2297544;
ECHA InfoCard	100.033.425
EC Number	236-783-2;
PubChem CID	3032611;
UNII	68VAV8QID7 (anhydrous) ; 163J4O4DFH (monohydrate) ;
CompTox Dashboard (EPA)	DTXSID40893690 ;
	InChI InChI=1S/2C2H5NO2.Cu/c23-1-2(4)5;/h21,3H2,(H,4,5);/q;;+2/p-2 Key: VVYPIVJZLVJPGU-UHFFFAOYSA-L;
	SMILES C(C(=O)[O-])N.C(C(=O)[O-])N.[Cu+2];
Properties
Chemical formula	C4H8CuN2O4
Molar mass	211.664 g·mol−1
Appearance	light blue, flake-like crystals (cis form)
Density	2.029 g/cm3
Melting point	212 °C (414 °F; 485 K) (decomp.)
Hazards
GHS pictograms
GHS Signal word	Warning
GHS hazard statements	H302, H315, H319, H400
GHS precautionary statements	P264, P270, P273, P280, P301+312, P302+352, P305+351+338, P321, P330, P332+313, P337+313, P362, P391, P501
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
	Infobox references

Copper(II) glycinate (IUPAC suggested name: bis(glycinato)copper(II)) refers to the coordination complex of copper(II) with two equivalents of glycinate, with the formula [Cu(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.[1][2]

All forms are blue solids, with varying degrees of water solubility. A practical application of the compound is as a source of dietary copper in animal feeds.[3]

Structure

Like most amino acid complexes, the glycinate forms a 5-membered chelate ring, with the glycinato ligand serving as a bidentate (κ²Ο,Ν) species.[1][4] The chelating ligands assume a square planar configuration around the copper atom as is common for tetracoordinate d⁹ complexes, calculated to be much lower in energy than the alternative tetrahedral arrangement.[2]

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 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.

All forms of the complex have been characterized crystallographically, the most commonly isolated one being the cis monohydrate (x = 1).[4]

Synthesis

A typical preparation of bis(glycinato)copper(II) (proceeding through a non-redox dissociative substitution mechanism) involves the heating of a copper(II) acetate solution in 1:1 aqueous ethanol, followed by the addition of aqueous glycine solution.

The precipitate collected upon cooling is identified as the cis isomer when prepared in this manner; isomerisation to the trans form occurs at higher temperatures via a ring-twisting mechanism.[1][2]

References

Delf, B. W.; Gillard, R. D.; O'Brien, P. (1979-01-01). "The isomers of α-amino-acids with copper(II). Part 5. The cis and trans isomers of bis(glycinato)copper(II), and their novel thermal isomerization". Journal of the Chemical Society, Dalton Transactions (8): 1301–1305. doi:10.1039/DT9790001301. ISSN 1364-5447.
Tautermann, Christofer S.; Sabolović, Jasmina; Voegele, Andreas F.; Liedl, Klaus R. (2004-02-01). "Mechanism of the Cis−Trans Isomerization of Bis(glycinato)copper(II)". The Journal of Physical Chemistry B. 108 (6): 2098–2102. doi:10.1021/jp0364497. ISSN 1520-6106.
Ward, J. D.; Spears, J. W. (1997). "Long-Term Effects of Consumption of Low-Copper Diets with or Without Supplemental Molybdenum on Copper Status, Performance, and Carcass Characteristics of Cattle". Journal of Animal Science. 75 (11): 3057–3065. doi:10.2527/1997.75113057x. PMID 9374323.
Casari, B. M.; Mahmoudkhani, A. H.; Langer, V. (2004). "A Redetermination of cis-Aquabis(glycinato-κ²N,O)copper(II)". Acta Crystallogr. E. 60 (12): m1949–m1951. doi:10.1107/S1600536804030041.

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[:0-1] Delf, B. W.; Gillard, R. D.; O'Brien, P. (1979-01-01). "The isomers of α-amino-acids with copper(II). Part 5. The cis and trans isomers of bis(glycinato)copper(II), and their novel thermal isomerization". Journal of the Chemical Society, Dalton Transactions (8): 1301–1305. doi:10.1039/DT9790001301. ISSN 1364-5447.

[:1-2] Tautermann, Christofer S.; Sabolović, Jasmina; Voegele, Andreas F.; Liedl, Klaus R. (2004-02-01). "Mechanism of the Cis−Trans Isomerization of Bis(glycinato)copper(II)". The Journal of Physical Chemistry B. 108 (6): 2098–2102. doi:10.1021/jp0364497. ISSN 1520-6106.

[3] Ward, J. D.; Spears, J. W. (1997). "Long-Term Effects of Consumption of Low-Copper Diets with or Without Supplemental Molybdenum on Copper Status, Performance, and Carcass Characteristics of Cattle". Journal of Animal Science. 75 (11): 3057–3065. doi:10.2527/1997.75113057x. PMID 9374323.

[:2-4] Casari, B. M.; Mahmoudkhani, A. H.; Langer, V. (2004). "A Redetermination of cis-Aquabis(glycinato-κ²N,O)copper(II)". Acta Crystallogr. E. 60 (12): m1949–m1951. doi:10.1107/S1600536804030041.