Vanadium(III) chloride

Vanadium trichloride is VCl3. This purple salt is a common precursor to other vanadium(III) complexes. VCl3 is paramagnetic: vanadium(III) has two unpaired electrons.

Structure of VCl3
VCl3 has the very common BI3 structure, a motif that features hexagonally closest-packed chloride framework with vanadium ions occupying the octahedral holes. VBr3 and VI3 adopt the same structure, but VF3 features a structure more closely related to ReO3.

Preparation of VCl3
VCl3 is prepared by simply heating VCl4 at 160-170 °C under a flowing stream of inert gas, which sweeps out the Cl2. The reaction is straightforward to monitor: the bright red liquid converts to a crusty purple solid. Further heating of VCl3 decomposes with volatilization of VCl4, leaving VCl2.

Reactions of VCl3
Adducts and derivatives of V(III) show a broad scala of colours.

Aqua complexes
VCl3 dissolves in water to give the hexahydrate, but the formula is deceptive. The salt is described by the formula [VCl2(H2O)4]Cl.2H2O. 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 from [VCl2(H2O)4]+ in aqueous solution gives the green ion [V(H2O)6]3+.

Other ligands
VCl3 forms complexes with many donor ligands. Representative examples include the red/pink tetrahydrofuran adduct VCl3(THF)3 and the green acetonitrile adduct VCl3(MeCN)3.

When treated with KCN, VCl3 converts to [V(CN)7]4-. It is typical for early metals to adopt high coordination numbers (more 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.

Reduction
Upon heating under H2 at 675 °C (but less than 700 °C), VCl3 reduces to greenish VCl2.
 * 2 VCl3 +   H2  →   2 VCl2  +  2 HCl

Precursor to organometallics
The remarkably reactive species V(mesityl)3 is formed from VCl3.
 * VCl3(THF)3 + 3 LiC6H2-2,4,6-Me3  →   V(C6H2-2,4,6-Me3)3(THF)  +  3 LiCl

This species binds CO and, under appropriate conditions, N2.

Suppliers

 * Sigma-Aldrich

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