Tantalum(III) chloride or tantalum trichloride is a non-stoichiometric chemical compound with a range of composition from TaCl<sub>2.9</sub> to TaCl<sub>3.1</sub> Anionic and neutral clusters containing Ta(III) chloride include [Ta<sub>6</sub>Cl<sub>18</sub>]<sup>4âÂÂ</sup> and [Ta<sub>6</sub>Cl<sub>14</sub>](H<sub>2</sub>O)<sub>4</sub>.
Tantalum(III) chloride is formed by reducing tantalum(V) chloride with tantalum metal. this is done by heating tantalum(III) chloride to 305 ðC, passing the vapour over tantalum foil at 600ð, and condensing the trichloride at 365 ðC. If the condensing region is kept at too high a temperature, then TaCl<sub>2.5</sub> deposits instead.
The trichloride can also be prepared by thermal decomposition of TaCl<sub>4</sub>, with removal of volatile TaCl<sub>5</sub>. TaCl<sub>5</sub> can be vapourised leaving behind TaCl<sub>3</sub>.
"Salt-free reduction" of a toluene solution of TaCl<sub>5</sub> with 1,4-disilyl-cyclohexadiene in the presence of ethylene produces a complex of TaCl<sub>3</sub>:
Above 500 ðC, TaCl<sub>3</sub> disproportionates further releasing TaCl<sub>5</sub>. TaCl<sub>3</sub> is insoluble in room temperature water, or dilute acid, but dissolves in boiling water. A blue-green solution is formed.
Tantalum(III) chloride can form complexes with some ligands as a monomer or dimer.
Complexes include Ta(=C-CMe<sub>3</sub>)(PMe<sub>3</sub>)<sub>2</sub>Cl<sub>3</sub>, [TaCl<sub>3</sub>(P(CH<sub>2</sub>C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>THF]<sub>2</sub>ü-N<sub>2</sub> and [TaCl<sub>3</sub>THF<sub>2</sub>]<sub>2</sub>ü-N<sub>2</sub> (dinitrogen complexes).
As a dimer, complexes include Ta<sub>2</sub>Cl<sub>6</sub>(SC<sub>4</sub>H<sub>8</sub>)<sub>3</sub> (SC<sub>4</sub>H<sub>8</sub>=tetrahydrothiophene). Ta<sub>2</sub>Cl<sub>6</sub>(SMe<sub>2</sub>)<sub>3</sub>, Ta<sub>2</sub>Cl<sub>6</sub>(thiane)<sub>3</sub> and Ta<sub>2</sub>Cl<sub>6</sub>(thiolane)<sub>3</sub> have a double bond between the two tantalum atoms, and two bridging chlorides, and a bridging ligand.