Titanium tetraiodide

Titanium tetraiodide
Names
	IUPAC name Titanium(IV) iodide
	Other names Titanium tetraiodide
Identifiers
CAS Number	7720-83-4 ;
3D model (JSmol)	Interactive image;
ChemSpider	99888 ;
ECHA InfoCard	100.028.868
EC Number	231-754-0;
PubChem CID	111328;
CompTox Dashboard (EPA)	DTXSID8064779 ;
	InChI InChI=1S/4HI.Ti/h41H;/q;;;;+4/p-4 Key: NLLZTRMHNHVXJJ-UHFFFAOYSA-J ; InChI=1/4HI.Ti/h41H;/q;;;;+4/p-4/rI4Ti/c1-5(2,3)4 Key: NLLZTRMHNHVXJJ-CDYINDSBAY;
	SMILES [Ti](I)(I)(I)I;
Properties
Chemical formula	TiI4
Molar mass	555.485 g/mol
Appearance	red-brown crystals
Density	4.3 g/cm3
Melting point	150 °C (302 °F; 423 K)
Boiling point	377 °C (711 °F; 650 K)
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
	Occupational safety and health (OHS/OSH):
Main hazards	violent hydrolysis; corrosive
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314
Precautionary statements	P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501
Related compounds
Other anions	Titanium(IV) bromide ; Titanium(IV) chloride ; Titanium(IV) fluoride
Other cations	Silicon tetraiodide ; Zirconium(IV) iodide ; Hafnium(IV) iodide
Related compounds	Titanium(III) iodide
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Titanium tetraiodide is an inorganic compound with the formula TiI₄. It is a black volatile solid, first reported by Rudolph Weber in 1863.^[2] It is an intermediate in the van Arkel–de Boer process for the purification of titanium.

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.^[3] 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–de Boer 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.^[3]

Production

Three methods are well known: 1) From the elements, typically using a tube furnace at 425 °C:^[4]

Ti + 2 I₂ → TiI₄

This reaction can be reversed to produce highly pure films of Ti metal.^[5]

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.^[6]

TiI₄ exhibits extensive reactivity toward alkenes and alkynes resulting in organoiodine derivatives. It also effects pinacol couplings and other C-C bond-forming reactions.^[7]