Vanadium(II) chloride is the inorganic compound with the formula VCl₂, and is the most reduced vanadium chloride. Vanadium(II) chloride is an apple-green solid that dissolves in water to give purple solutions.

Preparation, properties, and related compounds

Solid VCl₂ is prepared by thermal decomposition of VCl₃, which leaves a residue of VCl₂:

VCl₂ dissolves in water to give the purple hexaaquo ion [V(H₂O)₆]²⁺. Evaporation of such solutions produces crystals of [V(H₂O)₆]Cl₂.

Structure

Solid VCl₂ adopts the cadmium iodide structure, featuring octahedral coordination geometry. VBr₂ and VI₂ are structurally and chemically similar to the dichloride. All have the d³ configuration, with a quartet ground state, akin to Cr(III).

Vanadium dichloride is a powerful reducing species, being able to convert sulfoxides to sulfides, organic azides to amines, as well as reductively coupling some alkyl halides.

References

Vanadium trichloride is the inorganic compound with the formula VCl₃. This purple salt is a common precursor to other vanadium(III) complexes.

Structure

VCl₃ has the common BiI₃ 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. VCl₃ is paramagnetic and has two unpaired electrons.

Preparation and reactions

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 crusty purple solid. Further heating of VCl₃ decomposes with volatilization of VCl₄, leaving VCl₂. Upon heating under H₂ at 675 °C (but less than 700 °C), VCl₃ reduces to greenish VCl₂.

Vanadium trichloride catalyses the pinacol coupling reaction of benzaldehyde to 1,2-diphenyl-1,2-ethanediol by various reducing metals such as zinc:

Complexes

VCl₃ forms many adducts and derivatives with a broad scale of colours. 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⁺.

Vanadium tetrachloride is the inorganic compound with the formula VCl₄. This bright red liquid is a useful reagent for the preparation of other vanadium compounds.

Synthesis, bonding, basic properties

With one more valence electron than diamagnetic TiCl₄, VCl₄ is a paramagnetic liquid. It is one of only a few paramagnetic compounds that is liquid at room temperature.

VCl₄ is prepared by chlorination of vanadium metal. VCl₅ does not form; Cl₂ lacks the oxidizing power to attack VCl₄. In contrast, the heavier analogues NbCl₅ and TaCl₅ are stable and not particularly oxidizing. Of course, VF₅ does exist, reflecting the increased oxidizing power of F₂ vs Cl₂. Indicative of its oxidizing power, VCl₄ releases Cl₂ at its boiling point (standard pressure) to afford vanadium(III) chloride.

Reactions

Consistent with its high oxidizing power, VCl₄ reacts with HBr at -50 °C to produce VBr₃. The reaction proceeds via VBr₄, which releases Br₂ during warming to room temperature.