Titanium tetraiodide

Titanium tetraiodide is TiI4. It is a rare molecular binary metal iodide, consisting of isolated molecules of tetrahedral Ti(IV) centers; the other example is Ta2I10. Reflecting its molecular character, TiI4 can be distilled without decomposition at one atmosphere. The compound is a close relative to TiCl4. The difference in melting point between TiCl4 (m.p. -24 °C) and TiI4 (m.p. 150 °C) is comparable to the difference between the melting points of CCl4 (m.p. -23 °C) and CI4 (m.p. 168 °C), reflecting the stronger intermolecular van der Waals bonding in the iodides.

Production
Three methods are well known: 1) From the elements, typically using a tube furnace at 425 °C:
 * Ti + 2 I2 →  TiI4

This reaction can be reversed to produce highly pure films of Ti metal.

2) Exchange reaction from titanium tetrachloride and HI.
 * TiCl4 + 4 HI →  TiI4 + 4 HCl

3) Oxide-iodide exchange from aluminium iodide.
 * 3 TiO2 + 4 AlI3 →  3 TiI4  +  2 Al2O3

Reactions
Like TiCl4 and TiBr4, TiI4 forms adducts with Lewis bases, and it can also be reduced. When the reduction is conducted in the presence of Ti metal, one obtains polymeric Ti(III) and Ti(II) derivatives such as CsTi2I7 and the chain CsTiI3, respectively. As a solution in CH2Cl2, TiI4 exhibits some reactivity toward alkenes and alkynes resulting in organoiodine derivatives.