Vanadium iodide is the inorganic compound

Inorganic compound

Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the formula VI₃. This paramagnetic solid is generated by the reaction of vanadium

Vanadium

Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...

 powder with iodine

Iodine

Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....

 at around 500 °C. The black hygroscopic crystals, dissolving in water to give green solutions, characteristic of V(III) ions.

The purification of vanadium metal by the chemical transport reaction

Chemical transport reaction

In chemistry, a chemical transport reaction describes a process for purification and crystallization of non-volatile solids. The process is also responsible for certain aspects of mineral growth from the effluent of volcanoes. The technique is distinct from chemical vapor deposition, which...

 involving the reversible formation of vanadium(III) iodides in the presence of iodine

Iodine

Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....

 and its subsequent decomposition to yield pure metal:

2 V + 3 I₂ 2 VI₃

VI₃ crystallizes in the motif adopted by bismuth(III) iodide

Bismuth(III) iodide

Bismuth iodide is the inorganic compound with the formula BiI3. This gray-black solid is the product of the reaction of bismuth and iodide, which once was of interest in qualitative inorganic analysis....

: 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 VI₄, 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 VI₃ → VI₂ + VI₄ ΔH = 36.6 kcal/mol; ΔS = 38.7 eu