Titanium(III) chloride

Titanium(III) chloride is the chemical compound with the formula TiCl₃. This deceptively simple name describes several distinct species as well as a hydrated salt. TiCl₃ is one of the most common halides of titanium and is an important catalyst for the manufacture of polyolefins.

Additional recommended knowledge

How to ensure accurate weighing results every day?

Essential Laboratory Skills Guide

Weighing the right way

Electronic properties

In TiCl₃, each Ti atom has one d electron, rendering most of its forms paramagnetic, i.e. the substance is attracted into a magnetic field. The paramagnetism of TiCl₃'s contrasts with the diamagnetism (the property of being repelled from a magnetic field) of the trihalides of hafnium and zirconium. These heavier metals engage in metal-metal bonding, but the Ti(III) ion does not typically.

Solutions of titanium(III) chloride have violet coloration which arises from excitations of its d-electron. The colour is not very intense since the transition is forbidden.

Structure

Solid TiCl₃ can be obtained in one of four forms or polymorphs. These forms can be distinguished by crystallography as well as studies on their magnetic properties which probes exchange interactions.^[1]

Beta form

β-TiCl₃ crystallizes as brown needle. The structure of this material features chains of TiCl₆ octahedra that share opposite faces such that the closest Ti-Ti is 2.91 Å. This short distance allows strong metal-metal bonding.

"Violet layered" forms

The three violet layered" forms, named for their color and its tendency to flake, are called alpha, gamma, and delta. In α-TiCl₃, the chloride anions are hexagonal close-packed. In γ-TiCl₃, the chlorides anions are cubic close-packed. Finally, disorder in shift successions, causes an intermediate between alpha and gamma structures, called the delta (δ) form. The TiCl₆ share edges in each form, with 3.60 Å being the shortest distance between the titanium cations. This large distance between titanium cations precludes direct metal-metal bonding.

Ternary alkali halides

Caesium chloride treated with titanium(II) chloride and hexachlorobenzene produces crystalline CsTi₂Cl₇. The product contains 1:2 molar mixtures of CsCl and TiCl₃. CsCl₃ and Cl₄ stack alternatively in an ABAC sequence with Ti³⁺ in one quarter of the octahedral holes.^[2]

Synthesis and selected handling properties

Titanium(IV) chloride can be reduced to TiCl₃; this conversion is generally accomplished electrochemically. It is sold as a mixture with aluminium trichloride. This mixture can be separated to afford TiCl₃(THF)₃.^[3]

Ti³⁺ is prepared in situ as part of the method of analyzing titanium-containing samples such as ores. Thus, acidic solutions of Ti⁴⁺ are reduced using Jones reductor with amalgamated zinc.^[4] The resulting Ti³⁺ containing product is analyzed by redox titration.

TiCl₃ and most of its complexes are handled under an inert atmosphere to prevent reactions with oxygen. Slow deterioration occurs in air-exposed titanium trichloride, often results in erratic results, e.g. in reductive coupling reactions^[5].

Applications in Ziegler-Natta catalyst

TiCl₃ is a useful Ziegler-Natta catalyst, although the catalytic activities vary with the method of preparation.^[6]

Other reactions of Ti(III) chloride

TiCl₃ forms a variety of coordination complexes, most of which are octahedral. The light-blue crystalline adduct TiCl₃(THF)₃ forms when TiCl₃ is refluxed with tetrahydrofuran.^[7]

TiCl₃ + 3C₄H₈O → TiCl₃(OC₄H₈)₃

A dark green charge-neutral complex arises from complexation with dimethylamine:

TiCl₃ + 3Me₂NH → TiCl₃(NHMe₂)₃ + CH₃Cl

TiCl₃ reacts with acetylacetone to form a tris acetylacetonate complex.

TiCl₃ + 3NH₄(acac) → Ti(acac)₃ + 3NH₄Cl

The product is used as cross-linking agent for cellulose films used in polyethylene catalysts. Ti(acac)₃ air-oxidizes to give orange TiO(acac)₂, which is ineffective in cross-linking.^[8]

Above 200 °C, TiCl₃ undergoes ammonolysis.⁶

The ternary halides, such as A₃TiCl₆, have structures that depend on the cation (A) added.^[9]

References

1. ^ Starr, C.; Bitter, F.; Kaufman, A.R.Lippard, S. "Halides & Halide Complexes" in (1968) Progress in Inorganic Chemistry, Cotton (Ed.) Volume 9, (John Wiley & Sons, Inc.) pp. 6
2. ^ Holm, R. H. "Stabilized Low Oxidation States" in (1971) Progress in Inorganic Chemistry, Lippard, S. J. (Ed.) Volume 14, (John Wiley & Sons, Inc.) pp. 17
3. ^ Jongen, L. and Meyer, G. (2004). "Caesium heptaiododititanate(III), CsTi₂I₇". Zeitschrift für Anorganische und Allgemeine Chemie 630: 211-212. DOI
4. ^ Kisova, L.; Sotkova, S.; Konemdova, I. (1994). "Electrode Kinetics of the Ti(IV)/Ti(III) System in Water and in Water Dimethylformamide and Water Dimethyl Sulfoxide Mixed Solvents". Collection of Czechoslovak Chemical Communications 59: 1279-1286. DOI
5. ^ Fleming, M. P; McMurry, J. E. (1981). "Reductive Coupling of Carbonys to Alkenes: Adamantylideneadamantane". Organic Syntheses 60: 113. PDF
6. ^ Ueno, H.; Imanishi, K.; Ueki, S.; Kohara, T. (2000). "Kinetics Study of Propene Polymerization with Porous Titanium Trichloride". Chemical Society of Japan 7: 495. Abstract
7. ^ Jones, N. A.; Liddle, S. T.; Wilson, C.; Arnold, P. L. (2007). "Titanium(III) Alkoxy-N-heterocyclic Carbenes and a Safe, Low-Cost Route to TiCl₃(THF)₃". Organometallics, 26: 755 - 757. DOI: 10.1021/om060486d..
8. ^ Manzer, L. E., "Tetrahydrofuran Complexes of Selected Early Transition Metals", in (1982) Inorganic Syntheses, Flacker, J. P. (Ed.) Volume 21, pp. 137
9. ^ Cor, M.; Lewis, J.; Nyholm, R. S., S. "Titanium" in (1966) Progress in Inorganic Chemistry, Lippard, S. J. (Ed.) Volume 7, (John Wiley & Sons, Inc.) pp. 391
10. ^ Fowles, G. W. A. "Reacting Halides with Liquid Ammonia" in (1965) Progress in Inorganic Chemistry, Lippard, S. J. (Ed.) Volume 6, (John Wiley & Sons, Inc.) pp. 2
11. ^ Hinz, D.; Gloger, T. and Meyer, G. (2000). "Ternary halides of the type A₃MX₆. Part 9. Crystal structures of Na₃TiCl₆ and K₃TiCl₆". Zeitschrift für Anorganische und Allgemeine Chemie 626: 822-824. Abstract

Suppliers

• Fisher Scientific
• Sigma-Aldrich