Chemical Properties Of Titanium

Titanium is a group IVB element in the fourth period of the periodic table. Its atomic electronic structure is [Ar]3d²4s², with four valence electrons available for bonding. Therefore, its highest oxidation state in compounds is (Ⅳ). Since it belongs to the first transition series and has two unpaired 3d electrons, these can also participate in bonding, allowing titanium to have lower oxidation states (Ⅱ) and (Ⅲ).

In titanium (Ⅳ) compounds, the atoms are essentially inert. The Ti⁴⁺ ion has a radius of 60 pm, making it a high-charge, small-radius, high-field-strength cation with strong polarizing power towards coordinating ions. Therefore, Ti(Ⅳ) compounds are always covalent, similar in compound formation to Si(Ⅳ) and Sn(Ⅳ). For example, tetrachloride is a readily hydrolyzed, fuming liquid. In reality, there are no free Ti⁴⁺ ions or solvated ions; at most, (-Ti-O⁻)²⁺ chain-like hydrated ions exist in acidic solutions. In simple titanium(IV) compounds, titanium has a coordination number of 4. However, due to the presence of 3d orbitals in its atomic electronic structure, 4-coordinate titanium(IV) is a good Lewis acid and can accept ligands to extend the coordination number to 6. Compounds with coordination numbers of 5, 7, and 8 have also been found under specific conditions. Each coordination number corresponds to a specific molecular stereostructure. Titanium(III) is also an important valence of titanium; d1-configured trivalent titanium often forms octahedral complex ions, such as TiF63- and Ti(H2O)63+.

Besides the common oxidation states II, III, and IV, titanium in compounds can exhibit rare low oxidation states or negative oxidation states I, O, -I, and -II when combined with π-acidic ligands (ligands that can return electrons to the central titanium atom).