Titanium Tetrachloride - Properties and Structure

Properties and Structure

TiCl₄ is a dense, colourless distillable liquid, although crude samples may be yellow or even red-brown. It is one of the rare transition metal halides that is a liquid at room temperature, VCl₄ being another example. This property reflects the fact that TiCl₄ is molecular; that is, each TiCl₄ molecule is relatively weakly associated with its neighbours. Most metal chlorides are polymers, wherein the chloride atoms bridge between the metals. The attraction between the individual TiCl₄ molecules is weak, primarily van der Waals forces, and these weak interactions result in low melting and boiling points, similar to those of CCl₄.

Ti4+ has a "closed" electronic shell, with the same number of electrons as the inert gas argon. The tetrahedral structure for TiCl₄ is consistent with its description as a d0 metal center (Ti4+) surrounded by four identical ligands. This configuration leads to highly symmetrical structures, hence the tetrahedral shape of the molecule. TiCl₄ adopts similar structures to TiBr₄ and TiI₄; the three compounds share many similarities. TiCl₄ and TiBr₄ react to give mixed halides TiCl_{4 -x}Br_x, where x = 0, 1, 2, 3, 4. Magnetic resonance measurements also indicate that halide exchange is also rapid between TiCl₄ and VCl₄.

TiCl₄ is soluble in toluene and chlorocarbons, as are other non-polar species. Evidence exists that certain arenes form complexes of the type +. TiCl₄ reacts exothermically with donor solvents such as THF to give hexacoordinated adducts. Bulkier ligands (L) give pentacoordinated adducts TiCl₄L.