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.

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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.

References

• Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
• Young, R. C.; Smith, M. E. "Vanadium(III) Chloride" Inorganic Syntheses volume IV, page 128-130, 1953.
• Young, R. C.; Smith, M. E. "Vanadium(II) Chloride" Inorganic Syntheses volume IV, page 126-127, 1953.
• Manzer, L. E. "Tetrahydrofuran Complexes of Selected Early Transition Metals," Inorganic Synthesis. 21, 135-140, (1982).
• Vivanco, M.; Ruiz, J.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. "Chemistry of the vanadium-carbon .sigma. bond. 1. Insertion of carbon monoxide, isocyanides, carbon dioxide, and heterocumulenes into the V-C bond of Tris(mesityl)vanadium(III)" Organometallics1993 volume 12, 1794-1801. doi:10.1021/om00029a042
• Donovan, W. F.; Smith, P. W. "Crystal and Molecular Structures of Aquahalogenovanadium(1ii) Complexes. Part 1. X-Ray Crystal Structure of trans-Tetrakisaquadibromovanadium(III) Bromide Dihydrate and the lsomorphous Chloro-compound" Journal of the Chemical Society, Daltor Transactions." 1975, pages 894-896. doi:10.1039/DT9750000894