Vanadium(III) iodide
# Vanadium(III) iodide

Vanadium(III) iodide is the inorganic compound with the formula $VI_3.$ This paramagnetic solid is generated by the reaction of vanadium powder with iodine at around 500 °C. The black hygroscopic crystals dissolve in water to give green solutions, characteristic of V(III) ions.

The purification of vanadium metal by the chemical transport reaction involving the reversible formation of vanadium(III) iodides in the presence of iodine and its subsequent decomposition to yield pure metal:

    2 V + 3 $I_2$ ⇌ 2 $VI_3$

$VI_3$ crystallizes in the motif adopted by bismuth(III) iodide: the iodides are hexagonal-closest packed and the vanadium centers occupy one third of the octahedral holes.

When solid samples are heated, the gas contains $VI_4,$ which is probably the volatile vanadium component in the vapor transport method. Thermal decomposition of the triiodide leaves a residue of vanadium(II) iodide:

    2 $VI_3$ → $VI_2$ + $VI_4$ ΔH = 36.6 kcal/mol; ΔS = 38.7 e.u.
