Titanium tetraiodide

Titanium tetraiodide is the inorganic compound with the formula TiI₄. It is a rare molecular binary metal iodide, consisting of isolated molecules of tetrahedral Ti(IV) centers;^[1] 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.

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Production

Three methods are well known: 1) From the elements, typically using a tube furnace at 425 °C:^[2]

Ti + 2 I₂ → TiI₄

This reaction can be reversed to produce highly pure films of Ti metal.^[3]

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.^[4] As a solution in CH₂Cl₂, TiI₄ exhibits some reactivity toward alkenes and alkynes resulting in organoiodine derivatives.^[5]

References

1. ^ Tornqvist EGM, Libby WF (1979). "Crystal Structure, Solubility, and Electronic Spectrum of Titanium Tetraiodide". Inorganic Chemistry 18: 1792. DOI
2. ^ Lowery, R. N.; Fay, R. C. "Titanium(IV) Iodide" Inorganic Syntheses 1967, volume X, pages 1-6.
3. ^ Blumenthal WB, Smith H (1950). "Titanium tetraiodide, Preparation and Refining". Industrial and Engenieering Chemistry 2: 249. DOI
4. ^ Jongen, L.; Gloger, T.; Beekhuizen, J.; Meyer, G. "Divalent Titanium: The Halides ATiX₃ (A = K, Rb, Cs; X = Cl, Br, I)" Zeitschrift fur Anorganische und Allgemeine Chemie 2005, volume 631, pages 582-586.
5. ^ Shimizu, Makoto; Toyoda, Tadahiro; Baba, Toru. An Intriguing Hydroiodination of Alkenes and Alkynes with Titanium Tetraiodide. Synlett 2005, volume 16, pages 2516-2518.