Chromium(II) Acetate - Wikipedia

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Chromium(II) acetate
Names
IUPAC name Chromium(II) acetate hydrate
Other names chromous acetate,chromium diacetate, chromium(II) ethanoate
Identifiers
CAS Number
  • 14976-80-8 checkY
3D model (JSmol)
  • Interactive image
ChemSpider
  • 107397 checkY
ECHA InfoCard 100.224.848 Edit this at Wikidata
PubChem CID
  • 120304
RTECS number
  • AG3000000
UNII
  • H3FYF8441T checkY
CompTox Dashboard (EPA)
  • DTXSID50890519 Edit this at Wikidata
InChI
  • InChI=1S/2C2H4O2.Cr/c2*1-2(3)4;/h2*1H3,(H,3,4);/q;;+2/p-2 checkYKey: LRCIYVMVWAMTKX-UHFFFAOYSA-L checkY
  • InChI=1/2C2H4O2.Cr/c2*1-2(3)4;/h2*1H3,(H,3,4);/q;;+2/p-2Key: LRCIYVMVWAMTKX-NUQVWONBAT
SMILES
  • [Cr+2]1234([OH2])#[Cr+2]([OH2])(O[C-](C)O1)(O[C-](C)O2)(O(C)[C-]O3)O(C)[C-]O4
Properties
Chemical formula C8H16Cr2O10
Molar mass 376.198 g·mol−1
Appearance brick-red solid
Density 1.79 g/cm3
Melting point dehydrates
Solubility in water soluble in hot water, MeOH
Structure
Crystal structure monoclinic
Coordination geometry octahedralcounting the Cr–Cr bond
Dipole moment 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 ?) Infobox references
Chemical compound

Chromium(II) acetate hydrate, also known as chromous acetate, is the coordination compound with the formula Cr2(CH3CO2)4(H2O)2. This formula is commonly abbreviated Cr2(OAc)4(H2O)2. This red-coloured compound features a quadruple bond. It exists as the dihydrate and the anhydrous forms. Both are diamagnetic.

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

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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]

A quadruple bond between the two chromium atoms is proposed to arise from the overlap of four d-orbitals on each metal with the same orbitals on the other metal: the dz2 orbitals overlap to give a sigma bonding component, the dxz and dyz orbitals overlap to give two pi bonding components, and the dxy orbitals give a delta bond. This quadruple bond is also confirmed by the low magnetic moment and short intermolecular distance between the two atoms of 236.2 ± 0.1 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]

In the anhydrous chromous acetate, the Cr-Cr distance is 2.288 Å, noticeably shorter than Cr-Cr contact in the dihydrate.[3]

Subunit of the polymeric anhydrous chromous acetate

History

[edit]

Eugène-Melchior Péligot first reported a chromium(II) acetate in 1844. His material was apparently the dimeric Cr2(OAc)4(H2O)2.[4][5] The unusual structure, as well as that of copper(II) acetate, was uncovered in 1951.[6]

Preparation

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The preparation usually begins with reduction of an aqueous solution of a Cr(III) compound using zinc.[7] The resulting blue solution is treated with sodium acetate, which results in the rapid 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.[8]

Anhydrous chromium(II) acetate

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Heating dihydrated chromium(II) acetate at 100 °C gives the brown anhydrous compound, which is particularly sensitive to oxygen.[7]

The anhydrous form of chromium(II) acetate, and also related chromium(II) carboxylates, can be prepared from chromocene with elimination of cyclopentadiene:[9]

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

Reactions

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Chromium(II) acetate is a starting material for other chromium(II) compounds. For example, it reacts with acetylacetone to give chromous acetylacetonate:[7]

Cr2(O2CCH3)4(H2O)2 + 4 H2C(COCH3)2 → 2 Cr(CH3C(O)CHC(O)CH3)2 + 8 HO2CCH3 + 2 H2O

Also, many analogues have been prepared using other carboxylic acids in place of acetate and using different bases in place of the water.

Chromium(II) acetate has been used to dehalogenate organic compounds such as α-bromoketones and chlorohydrins.[10] The reactions appear to proceed via 1e− steps, and rearrangement products are sometimes observed.

See also

[edit]
  • Chromium(III) acetate
  • Chromium acetate hydroxide

References

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  1. ^ Cotton, F. A.; Walton, R. A. (1993). Multiple Bonds Between Metal Atoms. Oxford: Oxford University Press. ISBN 0-19-855649-7.
  2. ^ Cotton, F. A.; Hillard, E.A.; Murillo, C. A.; Zhou, H.-C. (2000). "After 155 Years, A Crystalline Chromium Carboxylate with a Supershort Cr–Cr Bond". J. Am. Chem. Soc. 122 (2): 416–417. doi:10.1021/ja993755i.
  3. ^ Cotton, F. Albert; Rice, Catherine E.; Rice, Gary W. (1977). "Crystal and Molecular Structure of Anhydrous Tetraacetatodichromium". Journal of the American Chemical Society. 99 (14): 4704–4707. Bibcode:1977JAChS..99.4704C. doi:10.1021/ja00456a029.
  4. ^ Péligot, E.-M. (1844). "Sur un nouvel oxide de chrome" [On a new chromium oxide]. C. R. Acad. Sci. (in French). 19: 609–618.
  5. ^ Péligot, E.-M. (1844). "Recherches sur le chrome" [Research on chrome]. Ann. Chim. Phys. (in French). 12: 527–548.
  6. ^ Van Niekerk, J. N.; Schoening, F. R. L. (1953). "X-Ray Evidence for Metal-to-Metal Bonds in Cupric and Chromous Acetate". Nature. 171 (4340): 36–37. Bibcode:1953Natur.171...36V. doi:10.1038/171036a0. S2CID 4292992.
  7. ^ a b c Ocone, L.R.; Block, B.P. (1966). Anyhdrous Chromium(II) Acetate, Chromium(II) Acetate 1-Hydrate, and Bis(2,4-Pentanedionato)Chromium (II). Inorganic Syntheses. Vol. 8. p. 125. doi:10.1002/9780470132395.ch33. ISBN 978-0-470-13167-1.
  8. ^ Jolly, W. L. (1970). The Synthesis and Characterization of Inorganic Compounds. Prentice Hall. pp. 442–445. ISBN 9780138799328.
  9. ^ Beneš, L.; Kalousová, J.; Votinský, J. (1985). "Reaction of Chromocene with Carboxylic Acids and Some Derivatives of Acetic Acid". J. Organomet. Chem. 290 (2): 147–151. doi:10.1016/0022-328X(85)87428-3.
  10. ^ Ray, T. (2004). "Chromium(II) Acetate". In Paquette, L. (ed.). Encyclopedia of Reagents for Organic Synthesis. New York, NY: J. Wiley & Sons. doi:10.1002/047084289X. hdl:10261/236866. ISBN 9780471936237.

Further reading

[edit]
  • Rice, Steven F.; Wilson, Randall B.; Solomon, Edward I. (1980). "Electronic Absorption Spectrum of Chromous Acetate Dihydrate and Related Binuclear Chromous Carboxylates". Inorg. Chem. 19 (11): 3425–3431. doi:10.1021/ic50213a042.
[edit] Wikimedia Commons has media related to Chromium(II) acetate.
  • http://www.molecules.org/coordcpds.html#Cr2OAc4H2O
  • [1] (outdated)
  • http://wwwchem.uwimona.edu.jm/courses/chromium.pdf
  • v
  • t
  • e
Chromium compounds
Chromium(0)
  • Cr(CO)6
Organochromium(0) compounds
  • Cr(C6H6)2
  • CrC6H6(CO)3
    • Chromium(I)
    • CrH
    Organochromium(I) compounds
    • Cr2(C5H5)2(CO)6
    Chromium(II)
    • CrH2
    • Cr3C2
    • Cr(C2O4)
    • Cr(CH3CO2)2
    • CrSi2
    • CrO
    • CrS
    • CrSO4
    • CrSe
    • CrF2
    • CrCl2
    • CrBr2
    • CrI2
    Organochromium(II) compounds
    • Cr(C5H5)2
    Chromium(II, III)
    • Cr3C2
    Chromium(III)
    • CrB
    • [Cr3O(CH3CO2)6(H2O)3]+[CH3CO2]−
    • CrN
    • Cr(NO3)3
    • CrPO4
    • Cr2O3
    • Cr(OH)3
    • Cr2S3
    • Cr2(SO4)3
    • Cr2Te3
    • CrF3
    • CrCl3
    • Cr(ClO4)3
    • CrBr3
    • CrI3
    Chromium(IV)
    • CrSi
    • CrO2
    • CrF4
    • CrCl4
    • CrBr4
    • CrI4
    Chromium(V)
    • K3Cr(O2)4
    • CrF5
    Chromium(VI)
    • CrO3
    • CrO(O2)2
    • H2CrO4/H2Cr2O7
    • CrO2F2
    • CrOF4
    • CrO2Cl2
    • CrO2Br2
    • [C5H5NH]+CrO3Cl−
    • CrF6 (hypothetical)
    Polyatomic ion
    • Chromate and dichromate
    • v
    • t
    • e
    Acetyl halides and salts of the acetate ion
    AcOH He
    LiOAc Be(OAc)2Be4O(OAc)6 B(OAc)3B2O(OAc)4 AcOAcROAc NH4OAc AcOOH FAcFOAc Ne
    NaOAcNaH(OAc)2 Mg(OAc)2 Al(OAc)3"ALSOL"Al(OAc)2OHAl(OH)2OAcAl2SO4(OAc)4 Si P S ClAcClOAc Ar
    KOAc Ca(OAc)2 Sc(OAc)3 Ti(OAc)4 VO(OAc)2 Cr(OAc)2Cr(OAc)3 Mn(OAc)2Mn(OAc)3 Fe(OAc)2Fe(OAc)3
    • Co(OAc)2
    • [CoO(OAc)py]4
    		 Ni(OAc)2 CuOAcCu(OAc)2 Zn(OAc)2 Ga(OAc)3 Ge As(OAc)3 Se BrAcBrOAc Kr
    RbOAc Sr(OAc)2 Y(OAc)3 Zr(OAc)4 Nb Mo(OAc)2 Tc Ru2(OAc)4ClRu(OAc)3 Rh2(OAc)4 Pd(OAc)2 AgOAc Cd(OAc)2 In(OAc)3 Sn(OAc)2Sn(OAc)4 Sb(OAc)3 Te IAcIOAcI(OAc)3 Xe
    CsOAc Ba(OAc)2 * Lu(OAc)3 Hf Ta W Re Os Ir Pt(OAc)2 Au(OAc)3 Hg2(OAc)2Hg(OAc)2 TlOAcTl(OAc)3 Pb(OAc)2Pb(OAc)4 Bi(OAc)3 Po At Rn
    Fr Ra ** Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
     
    * La(OAc)3 Ce(OAc)3 Pr(OAc)3 Nd(OAc)3 Pm Sm(OAc)3 Eu(OAc)3 Gd(OAc)3 Tb(OAc)3 Dy(OAc)3 Ho(OAc)3 Er(OAc)3 Tm(OAc)3 Yb(OAc)3
    ** Ac(OAc)3 Th(OAc)4 Pa
    • U(OAc)4
    • UO2(OAc)2
    		 NpO2OAcNpO2(OAc)2 PuO2(OAc)2 Am Cm Bk Cf Es Fm Md No

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