Titanium(II) chloride is the chemical compound with the formula TiCl<sub>2</sub>. The black solid has been studied only moderately, probably because of its high reactivity. Ti(II) is a strong reducing agent: it has a high affinity for oxygen and reacts irreversibly with water to produce H<sub>2</sub>. The usual preparation is the thermal disproportionation of TiCl<sub>3</sub> at 500 ðC. The reaction is driven by the loss of volatile TiCl<sub>4</sub>:
The method is similar to that for the conversion of VCl<sub>3</sub> into VCl<sub>2</sub> and VCl<sub>4</sub>.
TiCl<sub>2</sub> crystallizes as the layered CdI<sub>2</sub> structure. Thus, the Ti(II) centers are octahedrally coordinated to six chloride ligands.
Molecular complexes are known such as TiCl<sub>2</sub>(chel)<sub>2</sub>, where chel is DMPE (CH<sub>3</sub>)<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>P(CH<sub>3</sub>)<sub>2</sub> and TMEDA ((CH<sub>3</sub>)<sub>2</sub>NCH<sub>2</sub>CH<sub>2</sub>N(CH<sub>3</sub>)<sub>2</sub>). Such species are prepared by reduction of related Ti(III) and Ti(IV) complexes.
Unusual electronic effects have been observed in these species: TiCl<sub>2</sub>[(CH<sub>3</sub>)<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>P(CH<sub>3</sub>)<sub>2</sub>]<sub>2</sub> is paramagnetic with a triplet ground state, but Ti(CH<sub>3</sub>)<sub>2</sub>[(CH<sub>3</sub>)<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>P(CH<sub>3</sub>)<sub>2</sub>]<sub>2</sub> is diamagnetic.
A solid-state derivative of TiCl<sub>2</sub> is Na<sub>2</sub>TiCl<sub>4</sub>, which has been prepared by the reaction of Ti metal with TiCl<sub>3</sub> in a NaCl flux. This species adopts a linear chain structure wherein again the Ti(II) centers are octahedral with terminal, axial halides.