Vanadium(III) chloride

Anhydrous
Names
IUPAC names Vanadium(III) chloride Vanadium trichloride
Identifiers
CAS Number	7718-98-1 Y
3D model (JSmol)	anhydrous: Interactive image hexahydrate: Interactive image
ChemSpider	10801024 Y
ECHA InfoCard	100.028.859
EC Number	231-744-6
PubChem CID	62647
RTECS number	YW2800000
UN number	2475
CompTox Dashboard (EPA)	DTXSID3064776
InChI InChI=1S/3ClH.V/h3*1H;/q;;;+3/p-3 Y Key: HQYCOEXWFMFWLR-UHFFFAOYSA-K Y InChI=1/3ClH.V/h3*1H;/q;;;+3/p-3 Key: HQYCOEXWFMFWLR-DFZHHIFOAB
SMILES anhydrous: Cl[V](Cl)Cl hexahydrate: Cl[V-3](Cl)([OH2+])([OH2+])([OH2+])[OH2+].[Cl-].O.O
Properties
Chemical formula	VCl3
Molar mass	157.30 g/mol
Appearance	violet crystals (anhydrous) green crystals (hexahydrate)[1]
Density	2.8 g/cm3 (anhydrous) 1.84 g/cm3 (hexahydrate)
Melting point	350 °C (662 °F; 623 K)[2] (decomposes, anhydrous)
Solubility in water	soluble
Magnetic susceptibility (χ)	+3030.0·10−6 cm3/mol
Structure
Crystal structure	Trigonal, hR24[3]
Space group	R3, No. 148[3]
Lattice constant	a = 6.012 Å, b = 6.012 Å, c = 17.34 Å α = 90°, β = 90°, γ = 120°[3] (anhydrous)
Thermochemistry[4]
Heat capacity (C)	93.2 J mol−1 K−1
Std molar entropy (S⦵298)	131.0 J mol−1 K−1
Std enthalpy of formation (ΔfH⦵298)	-580.7 kJ/mol
Gibbs free energy (ΔfG⦵)	-511.2 kJ/mol
Hazards
GHS labelling:[5]
Pictograms
Signal word	Danger
Hazard statements	H302, H314
Precautionary statements	P260, P264, P270, P280, P301+P312+P330, P301+P330+P331, P303+P361+P353, P304+P340+P310, P305+P351+P338+P310, P363, P405, P501
NFPA 704 (fire diamond)	3 0 2
Flash point	Non-flammable
Safety data sheet (SDS)	Vanadium(III) Chloride
Related compounds
Other anions	Vanadium(III) fluoride Vanadium(III) bromide Vanadium(III) iodide
Other cations	Titanium(III) chloride Chromium(III) chloride Niobium(III) chloride Tantalum(III) chloride
Related compounds	Vanadium(II) chloride Vanadium(IV) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Vanadium(III) chloride describes the inorganic compound with the formula VCl₃ and its hydrates. It forms a purple anhydrous form and a green hexahydrate [VCl₂(H₂O)₄]Cl·2H₂O. These hygroscopic salts are common precursors to other vanadium(III) complexes and is used as a mild reducing agent.^[6]

VCl₃ has the common layered BiI₃ structure, a motif that features hexagonally closest-packed chloride framework with vanadium ions occupying the octahedral holes.^[7] VBr₃ and VI₃ adopt the same structure, but VF₃ features a structure more closely related to ReO₃.^[3] The V³⁺cation has a d² electronic configuration with two unpaired electrons, making the compound paramagnetic.^[8] VCl₃ is a Mott insulator and undergoes an antiferromagnetic transition at low temperatures.^[7][9]

Solid hexahydrate, [VCl₂(H₂O)₄]Cl·2H₂O, has a monoclinic crystal structure and consists of slightly distorted octahedral trans-[VCl₂(H₂O)₄]⁺ centers as well as chloride and two molecules of water of crystallization.^[10][11] The hexahydrate phase loses two water of crystallization to form the tetrahydrate if heated to 90 °C in a stream of hydrogen chloride gas.^[1]

Plan view of a single layer in the crystal structure of vanadium(III) chloride

Layer stacking in the crystal structure of vanadium(III) chloride

Unit cell of hexahydrate, featuring [VCl₂(H₂O)₄]⁺ centres

Solutions of vanadium(III) chloride in sulfuric acid and hydrochloric acid are used as electrolytes in vanadium redox batteries.^[12] It is also used as a mild Lewis acid in organic synthesis. One example of such is its use as a catalyst in the cleavage of the acetonide group.^[13] Another example of the use of VCl₃ as a reducing agent is shown in the determination of nitrate and nitrite concentration in water, where VCl₃ reduces nitrate to nitrite. This method is a safer alternative to the cadmium column method.^[14]

VCl₃ is prepared by heating VCl₄ at 160–170 °C under a flowing stream of inert gas, which sweeps out the Cl₂. The bright red liquid converts to a purple solid.^[15]

The vanadium oxides can also be used to produce vanadium(III) chloride. For example, vanadium(III) oxide reacts with thionyl chloride at 200 °C:^[15]

V₂O₃ + 3 SOCl₂ → 2 VCl₃ + 3 SO₂

The reaction of vanadium(V) oxide and disulfur dichloride also produces vanadium(III) chloride with the release of sulfur dioxide and sulfur.^[15]

The hexahydrate can be prepared by evaporation of acidic aqueous solutions of the trichloride.^[1]

Heating of VCl₃ decomposes with volatilization of VCl₄, leaving VCl₂ above 350 °C.^[2][16] Upon heating under H₂ at 675 °C (but less than 700 °C), VCl₃ reduces to greenish VCl₂.

2 VCl₃ + H₂ → 2 VCl₂ + 2 HCl

Comproportionation of vanadium trichloride and vanadium(V) oxides gives vanadium oxydichloride:^[17]

V₂O₅ + VOCl₃ + 3 VCl₃ → 6 VOCl₂

The heating of the hexahydrate does not give the anhydrous form, instead undergoes partial hydrolysis and forms vanadium oxydichloride at 160 °C. In an inert atmosphere, it forms a trihydrate at 130 °C and at higher temperatures, it forms vanadium oxychloride.^[18]

Vanadium trichloride catalyses the pinacol coupling reaction of benzaldehyde (PhCHO) to 1,2-diphenyl-1,2-ethanediol by various reducing metals such as zinc:^[19]

Zn + 2 H₂O + 2 PhCHO → (PhCH(OH))₂ + Zn(OH)₂

VCl₃ forms colorful adducts and derivatives with a broad scale of ligands. VCl₃ dissolves in water to give the aquo complexes. From these solutions, the hexahydrate [VCl₂(H₂O)₄]Cl^.2H₂O crystallizes. In other words, two of the water molecules are not bound to the vanadium, whose structure resembles the corresponding Fe(III) derivative. Removal of the two bound chloride ligands gives the green hexaaquo complex [V(H₂O)₆]³⁺.^[10][20]

With tetrahydrofuran, VCl₃ forms the red/pink complex VCl₃(THF)₃.^[22] Vanadium(III) chloride reacts with acetonitrile to give the green adduct VCl₃(MeCN)₃. When treated with KCN, VCl₃ converts to [V(CN)₇]⁴⁻ (early metals commonly adopt coordination numbers greater than 6 with compact ligands). Complementarily, larger metals can form complexes with rather bulky ligands. This aspect is illustrated by the isolation of VCl₃(NMe₃)₂, containing two bulky NMe₃ ligands. Vanadium(III) chloride is able to form complexes with other adducts, such as pyridine or triphenylphosphine oxide.^[20]

Vanadium(III) chloride as its thf complex is a precursor toV(mesityl)₃.^[23]

VCl₃(THF)₃ + 3 LiC₆H₂-2,4,6-Me₃ → V(C₆H₂-2,4,6-Me₃)₃(THF) + 3 LiCl