Technetium trichloride is an inorganic compound of technetium and chlorine with the formula TcCl<sub>3</sub>.
Two polymorphs of technetium trichloride are known. The ñ-polymorph is prepared as a black solid from ditechnetium(III) tetraacetate dichloride and hydrogen chloride at 300 ðC. It has a bioctahedral structure, consisting of triangular Tc<sub>3</sub>Cl<sub>9</sub> units with C<sub>3v</sub> symmetry, with each Tc atom coordinated to two Tc neighbors and five chloride ligands (Tc-Tc bond length 2.44 angstrom). The Tc-Tc distances are indicative of double bonded Tc atoms. Tc<sub>3</sub>Cl<sub>9</sub> is isostructural to its rhenium homologue, trirhenium nonachloride.
ò-TcCl<sub>3</sub> is obtained by the reaction between technetium metal and chlorine gas. Its structure consists of infinite layers of edge-sharing octahedra, similar to MoCl<sub>3</sub> and ReCl<sub>3</sub>, with distances that also indicate metal-metal bonding. It is less stable than ñ-TcCl<sub>3</sub> and slowly transforms into it.