Titanium tetrafluoride

Titanium(IV) fluoride is the inorganic compound with the formula TiF4. It is a white hygroscopic solid. In contrast to the other tetrahalides of titanium, it adopts a polymeric structure. In common with the other tetrahalides, TiF4 is a strong Lewis acid.

Preparation and structure
The traditional method involves treatment of titanium tetrachloride with excess hydrogen fluoride:
 * TiCl4 + 4 HF → TiF4 + 4 HCl

Purification is by sublimation, which involves reversible cracking of the polymeric structure. X-ray crystallography reveals that the Ti centres are octahedral, but conjoined in an unusual columnar structure.

Reactions
TiF4 forms adducts with many ligands. One example is the complex cis-TiF4(CH3CN)2, which is formed by treatment with acetonitrile. It is also used as a reagent in the preparation of organofluorine compounds. With fluoride, the cluster [Ti4F18]2- forms. It has an adamantane-like Ti4F6 core.

Related to its Lewis acidity, TiF4 forms a variety of hexafluorides also called hexafluorotitanates. Hexafluorotitanic acid has been used commercially to clean metal surfaces. These salts are stable at pH<4 in the presence of hydrogen fluoride, otherwise they hydrolyze to give oxides.