Chromium(II) chloride

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Chromium(II) chloride
Chromium(II) chloride.JPG
IUPAC name
Chromium(II) chloride
Other names
Chromous chloride
3D model (JSmol)
ECHA InfoCard 100.030.136 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 233-163-3
PubChem CID
RTECS number
  • GB5250000
UN number 3077
  • InChI=1S/2ClH.Cr/h2*1H;/q;;+2/p-2 Yes check.svgY
  • InChI=1/2ClH.Cr/h2*1H;/q;;+2/p-2
  • Cl[Cr]Cl
Molar mass 122.90 g·mol−1
AppearanceWhite to grey/green powder (anhydrous), very hygroscopic
Odor Odorless
Density 2.88 g/cm3 (24 °C) [1]
Melting point 824 °C (1,515 °F; 1,097 K)
51 °C (124 °F; 324 K)
tetrahydrate, decomposes [1]
Boiling point 1,302 °C (2,376 °F; 1,575 K)
anhydrous [1]
Soluble [1]
Solubility Insoluble in alcohol, ether
Acidity (pKa)2
+7230·10−6 cm3/mol
Orthorhombic (deformed rutile, anhydrous), oP6 [2]
Monoclinic (tetrahydrate) [3]
Pnnm, No. 58 (anhydrous) [2]
P21/c, No. 14 (tetrahydrate) [3]
2/m 2/m 2/m (anhydrous) [2]
2/m (tetrahydrate) [3]
a = 6.64 Å, b = 5.98 Å, c = 3.48 Å (anhydrous) [2]
α = 90°, β = 90°, γ = 90°
Octahedral (Cr2+, anhydrous) [2]
71.2 J/mol·K [1]
115.3 J/mol·K [1]
−395.4 kJ/mol [1]
−356 kJ/mol [1]
GHS labelling:
GHS-pictogram-exclam.svg [4]
H302, H315, H319, H335 [4]
P261, P305+P351+P338 [4]
NFPA 704 (fire diamond)
Lethal dose or concentration (LD, LC):
1870 mg/kg (rats, oral) [5]
Safety data sheet (SDS) Oxford MSDS
Related compounds
Other anions
Chromium(II) fluoride
Chromium(II) bromide
Chromium(II) iodide
Other cations
Chromium(III) chloride
Chromium(IV) chloride
Molybdenum(II) chloride
Tungsten(II) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Chromium(II) chloride describes inorganic compounds with the formula Cr Cl 2(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:

2 CrCl3 + H2 → 2 CrCl2 + 2 HCl

or by electrolysis.

On the laboratory scale, LiAlH4, zinc, and related reductants produce chromous chloride from chromium(III) precursors:

4 CrCl3 + LiAlH4 → 4 CrCl2 + LiCl + AlCl3 + 2 H2
2 CrCl3 + Zn → 2 CrCl2 + ZnCl2

CrCl2 can also be prepared by treating a solution of chromium(II) acetate with hydrogen chloride: [6]

Cr2(OAc)4 + 4 HCl → 2 CrCl2 + 4 AcOH

Treatment of chromium powder with concentrated hydrochloric acid gives a blue hydrated chromium(II) chloride, which can be converted to a related acetonitrile complex. [7]

Cr + n H2O + 2 HCl → CrCl2(H2O)n + H2

Structure and properties

Anhydrous CrCl2 is white [6] 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. [8]

Ball-and-stick model of chromium(II) chloride tetrahydrate. Chromium(II) chloride tetrahydrate.png
Ball-and-stick model of chromium(II) chloride tetrahydrate.

The hydrated derivative, CrCl2(H2O)4, forms monoclinic crystals with the P21/c space group. The molecular geometry is approximately octahedral consisting of four short Cr—O bonds (2.078 Å) arranged in a square planar configuration and two longer Cr—Cl bonds (2.758 Å) in a trans configuration. [3]


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.

Organic chemistry

Chromium(II) chloride is used as precursor to other inorganic and organometallic chromium complexes. Alkyl halides and nitroaromatics are reduced by CrCl2. The moderate electronegativity of chromium and the range of substrates that CrCl2 can accommodate make organochromium reagents very synthetically versatile. [9] It is a reagent in the Nozaki-Hiyama-Kishi reaction, a useful method for preparing medium-size rings. [10] It is also used in the Takai olefination to form vinyl iodides from aldehydes in the presence of iodoform. [11]

Related Research Articles

<span class="mw-page-title-main">Zinc chloride</span> Chemical compound

Zinc chloride is the name of inorganic chemical compounds with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, and are highly soluble in water. This salt is hygroscopic and even deliquescent. Zinc chloride finds wide application in textile processing, metallurgical fluxes, and chemical synthesis. No mineral with this chemical composition is known aside from the very rare mineral simonkolleite, Zn5(OH)8Cl2·H2O.

<span class="mw-page-title-main">Cerium(III) chloride</span> Chemical compound

Cerium(III) chloride (CeCl3), also known as cerous chloride or cerium trichloride, is a compound of cerium and chlorine. It is a white hygroscopic salt; it rapidly absorbs water on exposure to moist air to form a hydrate, which appears to be of variable composition, though the heptahydrate CeCl3·7H2O is known. It is highly soluble in water, and (when anhydrous) it is soluble in ethanol and acetone.

<span class="mw-page-title-main">Aluminium chloride</span> Chemical compound

Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula AlCl3. It forms hexahydrate with the formula [Al(H2O)6]Cl3, containing six water molecules of hydration. Both are colourless crystals, but samples are often contaminated with iron(III) chloride, giving a yellow color.

<span class="mw-page-title-main">Cobalt(II) chloride</span> Chemical compound

Cobalt(II) chloride is an inorganic compound of cobalt and chlorine, with the formula CoCl
. The compound forms several hydrates CoCl
, for n = 1, 2, 6, and 9. Claims of the formation of tri- and tetrahydrates have not been confirmed. The anhydrous form is a blue crystalline solid; the dihydrate is purple and the hexahydrate is pink. Commercial samples are usually the hexahydrate, which is one of the most commonly used cobalt compounds in the lab.

<span class="mw-page-title-main">Copper(II) chloride</span> Chemical compound

Copper(II) chloride is the chemical compound with the chemical formula CuCl2. The anhydrous form is yellowish brown but slowly absorbs moisture to form a blue-green dihydrate.

<span class="mw-page-title-main">Chromium(III) chloride</span> Chemical compound

Chromium(III) chloride (also called chromic chloride) describes any of several chemical compounds with the formula CrCl3 · xH2O, where x can be 0, 5, and 6. The anhydrous compound with the formula CrCl3 is a violet solid. The most common form of the trichloride is the dark green hexahydrate, CrCl3 · 6 H2O. Chromium chlorides find use as catalysts and as precursors to dyes for wool.

<span class="mw-page-title-main">Nickel(II) chloride</span> Chemical compound

Nickel(II) chloride (or just nickel chloride) is the chemical compound NiCl2. The anhydrous salt is yellow, but the more familiar hydrate NiCl2·6H2O is green. Nickel(II) chloride, in various forms, is the most important source of nickel for chemical synthesis. The nickel chlorides are deliquescent, absorbing moisture from the air to form a solution. Nickel salts have been shown to be carcinogenic to the lungs and nasal passages in cases of long-term inhalation exposure.

<span class="mw-page-title-main">Tantalum(V) chloride</span> Chemical compound

Tantalum(V) chloride, also known as tantalum pentachloride, is an inorganic compound with the formula TaCl5. It takes the form of a white powder and is commonly used as a starting material in tantalum chemistry. It readily hydrolyzes to form tantalum(V) oxychloride (TaOCl3) and eventually tantalum pentoxide (Ta2O5); this requires that it be synthesised and manipulated under anhydrous conditions, using air-free techniques.

<span class="mw-page-title-main">Chromium(II) acetate</span> 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. The preparation of chromous acetate once was a standard test of the synthetic skills of students due to its sensitivity to air and the dramatic colour changes that accompany its oxidation. It exists as the dihydrate and the anhydrous forms.

<span class="mw-page-title-main">Chromium(III) fluoride</span> Chemical compound

Chromium(III) fluoride is the name for the inorganic compounds with the chemical formula CrF3 as well as several related hydrates. The compound CrF3 is a green crystalline solid that is insoluble in common solvents, but the coloured hydrates [Cr(H2O)6]F3 and [Cr(H2O)6]F3•3H2O are soluble in water. The trihydrate is green, and the hexahydrate is violet. The anhydrous form sublimes at 1100–1200 °C.

<span class="mw-page-title-main">Chromyl chloride</span> Chemical compound

Chromyl chloride is the inorganic compound with the formula CrO2Cl2. It is a reddish brown compound that is a volatile liquid at room temperature, which is unusual for transition metal complexes.

<span class="mw-page-title-main">Takai olefination</span>

Takai olefination in organic chemistry describes the organic reaction of an aldehyde with a diorganochromium compound to form an alkene. It is a name reaction, referencing Kazuhiko Takai, who first reported it in 1986. In the original reaction, the organochromium species is generated from iodoform or bromoform and an excess of chromium(II) chloride and the product is a vinyl halide. One main advantage of this reaction is the E-configuration of the double bond that is formed. According to the original report, existing alternatives such as the Wittig reaction only gave mixtures.

<span class="mw-page-title-main">Nozaki–Hiyama–Kishi reaction</span>

The Nozaki–Hiyama–Kishi reaction is a nickel/chromium coupling reaction forming an alcohol from the reaction of an aldehyde with an allyl or vinyl halide. In their original 1977 publication, Tamejiro Hiyama and Hitoshi Nozaki reported on a chromium(II) salt solution prepared by reduction of chromic chloride by lithium aluminium hydride to which was added benzaldehyde and allyl chloride:

Metal acetylacetonates are coordination complexes derived from the acetylacetonate anion (CH
) and metal ions, usually transition metals. The bidentate ligand acetylacetonate is often abbreviated acac. Typically both oxygen atoms bind to the metal to form a six-membered chelate ring. The simplest complexes have the formula M(acac)3 and M(acac)2. Mixed-ligand complexes, e.g. VO(acac)2, are also numerous. Variations of acetylacetonate have also been developed with myriad substituents in place of methyl (RCOCHCOR′). Many such complexes are soluble in organic solvents, in contrast to the related metal halides. Because of these properties, acac complexes are sometimes used as catalyst precursors and reagents. Applications include their use as NMR "shift reagents" and as catalysts for organic synthesis, and precursors to industrial hydroformylation catalysts. C
in some cases also binds to metals through the central carbon atom; this bonding mode is more common for the third-row transition metals such as platinum(II) and iridium(III).

<span class="mw-page-title-main">Jones oxidation</span>

The Jones oxidation is an organic reaction for the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively. It is named after its discoverer, Sir Ewart Jones. The reaction was an early method for the oxidation of alcohols. Its use has subsided because milder, more selective reagents have been developed, e.g. Collins reagent.

<span class="mw-page-title-main">Chromyl fluoride</span> Chemical compound

Chromyl fluoride is an inorganic compound with the formula CrO2F2. It is a violet-red colored crystalline solid that melts to an orange-red liquid.

<span class="mw-page-title-main">Chromium(II) fluoride</span> Chemical compound

Chromium(II) fluoride is an inorganic compound with the formula CrF2. It exists as a blue-green iridescent solid. Chromium(II) fluoride is sparingly soluble in water, almost insoluble in alcohol, and is soluble in boiling hydrochloric acid, but is not attacked by hot distilled sulfuric acid or nitric acid. Like other chromous compounds, chromium(II) fluoride is oxidized to chromium(III) oxide in air.

In organophosphorus chemistry, an aminophosphine is a compound with the formula R3−nP(NR2)n where R = H or an organic substituent, and n = 0, 1, 2. At one extreme, the parent H2PNH2 is lightly studied and fragile, but at the other extreme tris(dimethylamino)phosphine (P(NMe2)3) is commonly available. Intermediate members are known, such as Ph2PN(H)Ph. These compounds are typically colorless and reactive toward oxygen. They have pyramidal geometry at phosphorus.

<span class="mw-page-title-main">Transition metal pyridine complexes</span>

Transition metal pyridine complexes encompass many coordination complexes that contain pyridine as a ligand. Most examples are mixed-ligand complexes. Many variants of pyridine are also known to coordinate to metal ions, such as the methylpyridines, quinolines, and more complex rings.

<span class="mw-page-title-main">Chromium(II) sulfide</span> Chemical compound

Chromium(II) sulfide is an inorganic compound of chromium and sulfur with the chemical formula CrS. The compound forms black hexagonal crystals, insoluble in water.


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