The moderate electronegativity of chromium and the range of substrates that CrCl 2 can accommodate make organochromium reagents very synthetically versatile. Alkyl halides and nitroaromatics are reduced by CrCl 2. Since the reduction potential of H + to H 2 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.Ĭhromium(II) chloride is used as precursor to other inorganic and organometallic chromium complexes. The reduction potential for Cr 3+ + e − ⇄ Cr 2+ is −0.41. 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. The hydrated derivative, CrCl 2(H 2O) 4, forms monoclinic crystals with the P2 1/c space group. Ball-and-stick model of chromium(II) chloride tetrahydrate. The Cr centres are octahedral, being distorted by the Jahn-Teller Effect. It crystallizes in the Pnnm space group, which is an orthorhombically distorted variant of the rutile structure making it isostructural to calcium chloride. Cr + n H 2O + 2 HCl → CrCl 2(H 2O) n + H 2 Structure and properties Īnhydrous CrCl 2 is white however commercial samples are often grey or green. Treatment of chromium powder with concentrated hydrochloric acid gives a blue hydrated chromium(II) chloride, which can be converted to a related acetonitrile complex. On the laboratory scale, LiAlH 4, zinc, and related reductants produce chromous chloride from chromium(III) precursors:Ĥ CrCl 3 + LiAlH 4 → 4 CrCl 2 + LiCl + AlCl 3 + 2 H 2 2 CrCl 3 + Zn → 2 CrCl 2 + ZnCl 2ĬrCl 2 can also be prepared by treating a solution of chromium(II) acetate with hydrogen chloride: Cr 2(OAc) 4 + 4 HCl → 2 CrCl 2 + 4 AcOH Chromium(II) chloride has no commercial uses but is used on a laboratory-scale for the synthesis of other chromium complexes.ĬrCl 2 is produced by reducing chromium(III) chloride either with hydrogen at 500 ☌: 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(H 2O) 4Cl 2. This distortion is a consequence of the Jahn–Teller effect that arises from the d 4 electron configuration of the chromium(II) ion.Chromium(II) chloride describes inorganic compounds with the formula Cr Cl 2(H 2O) n. Two of the six Cr–F bonds are long at 2.43 Å, and four are short near 2.00 Å. Like many difluorides, CrF 2 adopts a structure like rutile with octahedral molecular geometry about Cr(II) and trigonal geometry at F −. The reaction will proceed at room temperature but is typically heated to 100-200 ☌ to ensure completion: CrCl 2 + 2 HF → CrF 2 + 2 HCl The compound is prepared by passing anhydrous hydrogen fluoride over anhydrous chromium(II) chloride. Like other chromous compounds, chromium(II) fluoride is oxidized to chromium(III) oxide in air. 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. It exists as a blue-green iridescent solid. Chromium(II) fluoride is an inorganic compound with the formula CrF 2.
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