Chromium(III) chloride

Chromium(III) chloride
Names
Anhydrous
Hexahydrate
IUPAC names Chromium(III) chloride Chromium trichloride
Other names Chromic chloride
Identifiers
CAS Number	10025-73-7^Y 10060-12-5 (hexahydrate)^N
3D model (Jmol)	Interactive image
ChEBI	CHEBI:53351^Y
ChEMBL	ChEMBL1200528^N
ChemSpider	4954736^Y
ECHA InfoCard	100.030.023
PubChem	6452300
RTECS number	GB5425000
UNII	Z310X5O5RP^Y
InChI InChI=1S/3ClH.Cr/h31H;/q;;;+3/p-3^Y Key: QSWDMMVNRMROPK-UHFFFAOYSA-K^Y InChI=1/3ClH.Cr/h31H;/q;;;+2/p-3 Key: HUQISNLCWMVGCG-DFZHHIFOAJ InChI=1/3ClH.Cr/h3*1H;/q;;;+3/p-3 Key: QSWDMMVNRMROPK-DFZHHIFOAF
SMILES [Cr+3].[Cl-].[Cl-].[Cl-]
Properties
Chemical formula	CrCl₃
Molar mass	158.36 g/mol (anhydrous) 266.45 g/mol (hexahydrate)
Appearance	purple when anhydrous, dark green when hexahydrate
Density	2.87 g/cm³ (anhydrous) 1.760 g/cm³ (hexahydrate)
Melting point	1,152 °C (2,106 °F; 1,425 K) (anhydrous) 83 °C (hexahydrate)
Boiling point	1,300 °C (2,370 °F; 1,570 K) decomposes
Solubility in water	slightly soluble (anhydrous) 585 g/L (hexahydrate)
Solubility	insoluble in ethanol insoluble in ether, acetone
Acidity (pK_a)	2.4 (0.2M solution)
Magnetic susceptibility (χ)	+6890.0·10⁻⁶ cm³/mol
Structure
Crystal structure	YCl₃ structure
Coordination geometry	Octahedral
Hazards
Safety data sheet	ICSC 1316 (anhydrous) ICSC 1532 (hexahydrate)
EU classification (DSD)	Not listed
NFPA 704	0 3 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD₅₀ (median dose)	1870 mg/kg (oral, rat)
US health exposure limits (NIOSH):
PEL (Permissible)	TWA 1 mg/m³
REL (Recommended)	TWA 0.5 mg/m³
IDLH (Immediate danger)	250 mg/m³
Related compounds
Other anions	Chromium(III) fluoride Chromium(III) bromide Chromium(III) iodide
Other cations	Molybdenum(III) chloride Tungsten(III) chloride
Related compounds	Chromium(II) chloride Chromium(IV) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N (what is ^YN ?)
Infobox references

Chromium(III) chloride (also called chromic chloride) describes any of several compounds of with the formula CrCl₃(H₂O)_x, 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^.6H₂O. Chromium chloride finds uses as catalysts and as precursors to dyes for wool.

Anhydrous chromium(III) chloride adopts the YCl₃ structure, with Cr³⁺ occupying two thirds of the octahedral interstices in alternating layers of a pseudo-cubic close packed lattice of Cl⁻ ions. The absence of cations in alternate layers leads to weak bonding between adjacent layers. For this reason, crystals of CrCl₃cleave easily along the planes between layers, which results in the flaky (micaceous) appearance of samples of chromium(III) chloride.

Space-filling model of cubic close packing of chloride ions in the crystal structure of CrCl₃

Ball-and-stick model of part of a layer

Stacking of layers

Chromium(III) chlorides display the somewhat unusual property of existing in a number of distinct chemical forms (isomers), which differ in terms of the number of chloride anions that are coordinated to Cr(III) and the water of crystallization. The different forms exist both as solids, and in aqueous solutions. Several members are known of the series of [CrCl_3−n(H₂O)_n]^z+. The main hexahydrate can be more precisely described as [CrCl₂(H₂O)₄]Cl•2H₂O. It consists of the cation trans-[CrCl₂(H₂O)₄]⁺ and additional molecules of water and a chloride anion in the lattice. Two other hydrates are known, pale green [CrCl(H₂O)₅]Cl₂•H₂O and violet [Cr(H₂O)₆]Cl₃. Similar behaviour occurs with other chromium(III) compounds.

Anhydrous chromium(III) chloride may be prepared by chlorination of chromium metal directly, or indirectly by carbothermic chlorination of chromium(III) oxide at 650–800 °C

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