Titanium tetriodide

Titanium tetraiodide
IUPAC name

Titanium(IV) iodide
Other names

Titanium tetraiodide
Identifiers
CAS number 7720-83-4
PubChem 111328
Properties
Molecular formula TiI4
Molar mass 555.485 g/mol
Appearance red-brown crystals
Density 4.3 g/cm3
Melting point

150 °C
Boiling point

377 °C
Solubility in water hydrolysis
Solubility in other solvents soluble in CH2Cl2
CHCl3
CS2
Structure
Crystal structure cubic (a = 12.21 Å)
Coordination
geometry		 tetrahedral
Dipole moment 0 D
Hazards
R-phrases 34-37
S-phrases 26-36/37/39-45
Main hazards violent hydrolysis
corrosive
Related compounds
Related compounds titanium tetrachloride,
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Titanium tetraiodide is an inorganic compound with the formula TiI4. It is a black volatile solid. It is an intermediate in the Van Arkel process for the purification of titanium.

Contents

Physical properties

TiI4 is a rare molecular binary metal iodide, consisting of isolated molecules of tetrahedral Ti(IV) centers. The Ti-I distances are 261 pm.[1] Reflecting its molecular character, TiI4 can be distilled without decomposition at one atmosphere; this property is the basis of its use in the Van Arkel process. 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.

Two polymorphs of TiI4 exist, one of which is highly soluble in organic solvents. In the less soluble cubic form, the Ti-I distances are 261 pm.[1]

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. ^ a b Tornqvist, E. G. M.; Libby, W. F. (1979). "Crystal Structure, Solubility, and Electronic Spectrum of Titanium Tetraiodide". Inorganic Chemistry 18 (7): 1792–1796. doi:10.1021/ic50197a013.  DOI
  2. ^ Lowery, R. N.; Fay, R. C. "Titanium(IV) Iodide" Inorganic Syntheses 1967, volume X, pages 1-6. doi:10.1002/9780470132418.ch1
  3. ^ Blumenthal, W.B.; 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. doi:10.1002/zaac.200400464
  5. ^ Shimizu, Makoto; Toyoda, Tadahiro; Baba, Toru "An Intriguing Hydroiodination of Alkenes and Alkynes with Titanium Tetraiodide" Synlett 2005, volume 16, pages 2516-2518. doi:10.1055/s-2005-872679