Chromium(II) chloride
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_chloride.JPG) |
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| Names | |
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IUPAC name
Chromium(II) chloride
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| Other names
Chromous chloride
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| Identifiers | |
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3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.030.136 |
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PubChem CID
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| RTECS number | GB5250000 |
| UNII | |
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| Properties | |
| Cl2Cr | |
| Molar mass | 122.90 g·mol−1 |
| Appearance | White to grey/green powder (anhydrous), very hygroscopic |
| Odor | Odorless |
| Density | 2.88 g/cm3 (24 °C) |
| Melting point | 824 °C (1,515 °F; 1,097 K) anhydrous 51 °C (124 °F; 324 K) tetrahydrate, decomposes |
| Boiling point | 1,302 °C (2,376 °F; 1,575 K) anhydrous |
| Soluble | |
| Solubility | Insoluble in alcohol, ether |
| Acidity (pKa) | 2 |
| +7230·10−6 cm3/mol | |
| Structure | |
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Orthorhombic (deformed rutile, anhydrous), oP6 Monoclinic (tetrahydrate) |
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| Pnnm, No. 58 (anhydrous) P21/c, No. 14 (tetrahydrate) |
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| 2/m 2/m 2/m (anhydrous) 2/m (tetrahydrate) |
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a = 6.64 Å, b = 5.98 Å, c = 3.48 Å (anhydrous)
α = 90°, β = 90°, γ = 90°
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| Octahedral (Cr2+, anhydrous) | |
| Thermochemistry | |
| 71.2 J/mol·K | |
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Std molar
entropy (S |
115.3 J/mol·K |
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Std enthalpy of
formation (ΔfH |
−395.4 kJ/mol |
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Gibbs free energy (ΔfG˚)
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−356 kJ/mol |
| Hazards | |
| Safety data sheet | Oxford MSDS |
| GHS pictograms |  |
| GHS signal word | Warning |
| H302, H315, H319, H335 | |
| P261, P305+351+338 | |
| NFPA 704 | |
| Lethal dose or concentration (LD, LC): | |
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LD50 (median dose)
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1870 mg/kg (rats, oral) |
| Related compounds | |
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Other anions
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Chromium(II) fluoride Chromium(II) bromide Chromium(II) iodide |
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Other cations
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Chromium(III) chloride Chromium(IV) chloride Molybdenum(II) chloride Tungsten(II) chloride |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is   ?) |
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| Infobox references | |
Chromium(II) chloride describes inorganic compounds with the formula CrCl2(H2O)n. The anhydrous solid is white when pure, however commercial samples are often grey or green; it is hygroscopic and readily dissolves in water to give bright blue air-sensitive solutions of the tetrahydrate Cr(H2O)4Cl2. Chromium(II) chloride has no commercial uses but is used on a laboratory-scale for the synthesis of other chromium complexes.
CrCl2 is produced by reducing chromium(III) chloride either with hydrogen at 500 °C:
or by electrolysis.
Small scale preparations can use LiAlH4, Zinc or related reagents, to reduce CrCl3
CrCl2 can also be prepared by treating a solution of chromium(II) acetate with hydrogen chloride.
Anhydrous CrCl2 is white however commercial samples are often grey or green. It crystallizes in the Pnnm space group, which is an orthorhombically distorted variant of the rutile structure; making it isostructural to calcium chloride. The Cr centres are octahedral, being distorted by the Jahn-Teller Effect.
The hydrated derivative, CrCl2(H2O)4, forms monoclinic crystals with the P21/c space group. The molecular geometry is approximately square planar with Cr—O distances of 2.078 Å and two Cr—Cl distances of 2.758 Å.
The reduction potential for Cr3+ + e− ⇄ Cr2+ is −0.41. Since the reduction potential of H+ to H2 in acidic conditions is +0.00, the chromous ion has sufficient potential to reduce acids to hydrogen, although this reaction does not occur without a catalyst.
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