Chromium(II) acetate



Chromium(II) acetate
IUPAC name Chromium(II) acetate hydrate
Other names chromous acetate,
chromium diacetate
Identifiers
CAS number 14976-80-8
RTECS number AG3000000
Properties
Molecular formula C8H16Cr2O10
Molar mass 376.2 g/mol
Appearance brick-red solid
Density 1.79 g/cm3
Melting point

dehydrates >100C

Solubility in water soluble in hot water, MeOH
Structure
Crystal structure monoclinic
Coordination
geometry 		octahedral
counting the Cr-Cr bond
Molecular shape quadruple Cr--Cr bond
Dipole moment 0 D
Hazards
Main hazards could react exothermically in air
Related Compounds
Related compounds Cu2(OAc)4(H2O)2
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Chromium(II) acetate, better known as chromous acetate, is the compound Cr2(CH3CO2)4(H2O)2. This formula is commonly abbreviated Cr2(OAc)4(H2O)2. This compound and some of its simple derivatives illustrate one of the most remarkable properties of some anhydrous forms.

Cr2(OAc)4(H2O)2 is a reddish diamagnetic powder, although diamond-shaped tabular ionic, Cr2(OAc)4(H2O)2 exhibits poor solubility in water and methanol.

Structure

The Cr2(OAc)4(H2O)2 molecule contains two atoms of Cu2(OAc)4(H2O)2, although these species do not have such short M---M contacts.[1]

The quadruple bond between the two chromium atoms arises from the overlap of four magnetic moment and short intermolecular distance between the two atoms of 236.2±0.1 picometers.The Cr-Cr distances are even shorter, 184 pm being the record, when the axial ligand is absent or the carboxylate is replaced with isoelectronic nitrogenous ligands.[2]

History

copper(II) acetate, was uncovered in 1951.[4]

Preparation

An aqueous solution of a Cr(III) compound is first reduced to the chromous state using precipitates as a bright red powder.

Cr6+ + 2Zn → Cr2+ + 2Zn2+
2 Cr2+ + 4 OAc- + 2 H2O → Cr2(OAc)4(H2O)2

The synthesis of Cr2(OAc)4(H2O)2 has been traditionally used to test the synthetic skills and patience of inorganic laboratory students in universities because the accidental introduction of a small amount of air into the apparatus is readily indicated by the discoloration of the otherwise bright red product.[6] An alternative route to related chromium(II) carboxylates starts with chromocene:

4 HO2CR + 2 Cr(C5H5)2 → Cr2(O2CR)4 + 4 C5H6

The advantage to this method is that it provides anhydrous derivatives.

Because it is so easily prepared, Cr2(OAc)4(H2O)2 is often used as a starting material for other, chromium(II) compounds. Also many analogues have been prepared using other carboxylic acids in place of acetate and using different bases in place of the water.

Applications

Cr2(OAc)4(H2O)2 is used occasionally to dehalogenate organic compounds such as α-bromoketones and chlorohydrins.[7] The reactions appear to proceed via 1e- steps, and rearrangement products are sometimes observed.

Many other applications exist, including those in the polymer industry.[8]

References

  1. ^ Cotton, F. A.; Walton, R. A. “Multiple Bonds Between Metal Atoms” Oxford (Oxford): 1993. ISBN 0-19-855649-7.
  2. ^ Cotton, F. A.; Hillard, E.A.; Murillo, C. A.; Zhou, H.-C. "After 155 Years, A Crystalline Chromium Carboxylate with a Supershort Cr-Cr Bond" Journal of the American Chemical Society, 2000 volume 122 , pages 416-417. doi:10.1021/ja993755i
  3. ^ Peligot, E. C. R. Acad. Sci. 1844, volume 19, page 609ff. (b) Peligot, E. Ann. Chim. Phys. 1844, volume 12, pages 528ff.
  4. ^ van Niekerk, J. N. Schoening, F. R. L. “X-Ray Evidence for Metal-to-Metal Bonds in Cupric and Chromous Acetate” Nature 1953, volume 171, pages 36-37. doi:10.1038/171036a0.
  5. ^ Ocone, L.R.; Block, B.P. (1966). Inorganic Syntheses, 125-129. 
  6. ^ Jolly, W. L. (1970). The Synthesis and Characterization of Inorganic Compounds. Prentice Hall, 442-445. 
  7. ^ Ray, T. "Chromium(II) Acetate" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289
  8. ^ Lee, M. “Graft Copolymerization of Styrene on Rubber Containing Halogen by Chromous Acetate.” Journal of Polymer Science, 1976, volume 14, pages 961-971.

Further reading

  • Rice, S. F. “Electronic Absorption Spectrum of Chromous Acetate Dihydrate and Related Binuclear Chromous Carboxylates.” Inorg. Chem. 19 (1980):3425-3431.doi:10.1021/ic50213a042
 
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