Titanate

In chemistry, titanate usually refers to inorganic compounds composed of titanium oxides. In some cases, the term is used more generally for any titanium-containing anion, e.g. [TiCl₆]²⁻ and [Ti(CO)₇]²⁻. This article focuses on the oxides.

Many kinds of titanium oxides are known, and some are commercially important. Typically these materials are white, diamagnetic, high-melting, and insoluble in water. They are often prepared at high temperatures, e.g. using tube furnaces, from titanium dioxide. In virtually all cases, titanium achieves octahedral coordination geometry.^[1]

Orthotitanates

Orthotitanates have the formulae M₂TiO₄ where M is divalent. An example of such a material is the magnesium titanate (Mg₂TiO₄), which adopts the spinel structure. Li₂TiO₃ is not considered a titanate since it adopts the rock-salt structure, and does not feature an identifiable titanium anion. Orthotitanates almost never feature identifiable TiO₄⁴⁻ centres, an exception being Ba₂TiO₄.^[2]

Titanic acid and its esters

Also called orthotitanic acid or titanium hydroxide, the substance H₄TiO₄ (CASNo 20338-08-3) is called titanic acid. This material, which is not well defined, is obtained by hydrolysis of TiCl₄.^[3] The solid is unstable with respect to loss of water and formation of titanium dioxide. "Esters" of orthotitanic acid are known, however; one example being titanium isopropoxide. Esters derived from smaller alcohols adopt more complex structures wherein titanium does achieve octahedral coordination,

Metatitanates

The metatitanates have the formula MTiO₃, where again M is divalent. They do not feature discrete TiO₃²⁻ centres. Some crystallize in a hexagonal closest packing motif seen in corundum. This motif is illustrated by the commercially important mineral ilmenite (FeTiO₃). Alternatively, some materials with the formula MTiO₃ crystallize in the motif known as Perovskite (structure), which is also the name of the mineral form of calcium titanate (CaTiO₃). Barium titanate is a ferroelectric peroviskite.^[1]

Complex titanates

More complex titanates are also known, such as bismuth titanate, Bi₄Ti₃O₁₂.^[4]

References

1. Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 1121–23. ISBN 0-08-022057-6..
2. Wu, Kang Kun; Brown, I. D. (10 April 1973). "The Crystal Structure of β-Barium Orthotitanate, β-Ba₂TiO₄, and the Bond Strength-Bond Length Curve of Ti-O". Acta Crystallographica B29: 2009–2012. doi:10.1107/S0567740873005959.
3. Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 421.
4. Galasso, F. S.; Kestigan, M. (2007), "Bismuth Titanate, Bi₄Ti₃O₁₂", Inorg. Synth. 30: 121, doi:10.1002/9780470132616.ch24.