Titanium tetrafluoride explained

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:^[1]

TiCl₄ + 4 HF → TiF₄ + 4 HClPurification is by sublimation, which involves reversible cracking of the polymeric structure.^[2] X-ray crystallography reveals that the Ti centres are octahedral, but conjoined in an unusual columnar structure.^[3]

Reactions

TiF₄ forms adducts with many ligands. One example is the complex cis-TiF₄(CH₃CN)₂, which is formed by treatment with acetonitrile.^[4] It is also used as a reagent in the preparation of organofluorine compounds.^[5] With fluoride, the cluster [Ti₄F₁₈]^2- forms. It has an adamantane-like Ti₄F₆ core.^[6]

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.^[1]

Notes and References

1. Book: 10.1002/0471238961.2009200113051908.a01 . Fluorine Compounds, Inorganic, Titanium . Kirk-Othmer Encyclopedia of Chemical Technology . 2000 . Meshri . Dayal T. . 978-0-471-48494-3 .
2. Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 200.
3. Bialowons, H.. Mueller, M.. Mueller, B.G.. Titantetrafluorid - Eine Überraschend einfache Kolumnarstruktur. Zeitschrift für Anorganische und Allgemeine Chemie. 1995. 621. 7 . 1227–1231. 10.1002/zaac.19956210720.
4. A survey of Titanium Fluoride Complexes, Their Preparation, Reactivity, and Applications. Nikiforov, Grigory B.. Roesky, Herbert W.. Koley, Debasis. Coordination Chemistry Reviews . 2014. 258-259. 16–57. 10.1016/j.ccr.2013.09.002.
5. Book: 10.1002/047084289X.rn00123.pub2 . Titanium(IV) Fluoride . Encyclopedia of Reagents for Organic Synthesis . 2014 . Blizzard . T. A. . Sikervar . Vikas . 1–5 . 978-0-470-84289-8 .
6. 10.1021/ic9009338 . Poly[perfluorotitanate(IV)] Salts of [H₃O]⁺, Cs⁺, [Me₄N]⁺, and [Ph₄P]⁺ and about the Existence of an Isolated [Ti₂F₉]⁻ Anion in the Solid State . 2009 . Mazej . Zoran . Goreshnik . Evgeny . Inorganic Chemistry . 48 . 14 . 6918–6923 . 19545141 .