Titanium(IV) hydride (systematically named titanium tetrahydride) is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the

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. It has not yet been obtained in bulk, hence its bulk properties remain unknown. However, molecular titanium(IV) hydride has been isolated in solid gas matrices. The molecular form is a colourless gas, and very unstable toward thermal decomposition. As such the compound is not well characterised, although many of its properties have been calculated via computational chemistry.

Synthesis and stability

Titanium(IV) hydride was first produced in 1963 by the photodissociation of mixtures of and , followed by immediate mass spectrometry. Rapid analysis was required as titanium(IV) hydride is extremely unstable. Computational analysis of has given a theoretical bond dissociation energy (relative to M+4H) of 132 kcal/mole. As the dissociation energy of is 104 kcal/mole the instability of can be expected to be thermodynamic; with it dissociating to metallic titanium and

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

: : (76 kcal/mole) , along with other unstable molecular titanium hydrides, (TiH, , and polymeric species) has been isolated at low temperature following laser ablation of titanium.

Structure

It is suspected that within solid titanium(IV) hydride, the molecules form aggregations (

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s), being connected by covalent bonds. Calculations suggest that is prone to dimerisation. This largely attributed to the electron deficiency of the monomer and the small size of the hydride ligands; which allows dimerisation to take place with a very low energy barrier as there is a negligible increase in inter-ligand repulsion. The dimer is a calculated to be a fluxional molecule rapidly inter-converting between a number of forms, all of which display bridging hydrogens. This is an example of three-center two-electron bonding. Monomeric titanium(IV) hydride is the simplest transition metal molecule that displays sd³ orbital hybridisation.

References

{{Hydrides by group Titanium(IV) compounds Metal hydrides