Chromium(II) acetate

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Chromium(II) acetate
Names
IUPAC name
Chromium(II) acetate hydrate
Other names
chromous acetate,
chromium diacetate,
chromium(II) ethanoate
Identifiers
3D model (
JSmol
)
ChemSpider
ECHA InfoCard
 100.224.848 Edit this at Wikidata
RTECS number
  • AG3000000
UNII
  • InChI=1S/2C2H4O2.Cr/c2*1-2(3)4;/h2*1H3,(H,3,4);/q;;+2/p-2 checkY
    Key: LRCIYVMVWAMTKX-UHFFFAOYSA-L checkY
  • InChI=1/2C2H4O2.Cr/c2*1-2(3)4;/h2*1H3,(H,3,4);/q;;+2/p-2
    Key: LRCIYVMVWAMTKX-NUQVWONBAT
  • [Cr+2]1234([OH2])#[Cr+2]([OH2])(O[C-](C)O1)(O[C-](C)O2)(O(C)[C-]O3)O(C)[C-]O4
Properties
C8H16Cr2O10
Molar mass 376.198 g·mol−1
Appearance brick-red solid
Density 1.79 g/cm3
Melting point dehydrates
soluble in hot water, MeOH
-5104.0·10−6 cm3/mol
Structure
monoclinic
octahedral
counting the Cr–Cr bond
0 D
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 could react exothermically in air
Related compounds
Related compounds
 Rh2(OAc)4(H2O)2
Cu2(OAc)4(H2O)2, molybdenum(II) acetate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Chromium(II) acetate hydrate, also known as chromous acetate, is the

dihydrate and the anhydrous
forms.

Cr2(OAc)4(H2O)2 is a reddish

diamagnetic powder, although diamond-shaped tabular crystals can be grown. Consistent with the fact that it is nonionic, Cr2(OAc)4(H2O)2 exhibits poor solubility in water and methanol
.

Chromium(II) acetate (aqueous solution)

Structure

The Cr2(OAc)4(H2O)2 molecule contains two atoms of chromium, two ligated molecules of water, and four acetate bridging ligands. The coordination environment around each chromium atom consists of four oxygen atoms (one from each acetate ligand) in a square, one water molecule (in an axial position), and the other chromium atom (opposite the water molecule), giving each chromium centre an octahedral geometry. The chromium atoms are joined by a quadruple bond, and the molecule has D4h symmetry (ignoring the position of the hydrogen atoms). The same basic structure is adopted by Rh2(OAc)4(H2O)2 and 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

pm. 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

dimeric Cr2(OAc)4(H2O)2.[3][4] The unusual structure, as well as that of copper(II) acetate, was uncovered in 1951.[5]

Preparation

The preparation usually begins with reduction of an aqueous solution of a Cr(III) compound using

precipitation
of chromous acetate as a bright red powder.

2 Cr3+ + Zn → 2 Cr2+ + Zn2+
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.[7] The anhydrous form of chromium(II) acetate, and also related chromium(II) carboxylates, can be prepared from chromocene:

4 RCO2H + 2 Cr(C5H5)2 → Cr2(O2CR)4 + 4 C5H6

This method provides anhydrous derivatives in a straightforward manner.[8]

Because it is so easily prepared, Cr2(OAc)4(H2O)2 is 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

Chromium(II) acetate has few practical applications. It has been used to dehalogenate organic compounds such as α-bromoketones and

chlorohydrins.[9]
The reactions appear to proceed via 1e− steps, and rearrangement products are sometimes observed.

Because the compound is a good reducing agent, it will reduce the O2 found in air and can be used as an oxygen scrubber.

See also

References

  1. ISBN 0-19-855649-7
    .
  2. doi:10.1021/ja993755i
    .
  3. C. R. Acad. Sci.
    (in French). 19: 609–618.
  4. Ann. Chim. Phys.
    (in French). 12: 527–548.
  5. S2CID 4292992
    .
  6. ISBN 978-0-470-13239-5. {{cite book}}: |journal= ignored (help
    )
  7. ISBN 9780138799328
    .
  8. doi:10.1016/0022-328X(85)87428-3
    .
  9. ISBN 9780471936237
    .

Further reading

External links

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