The α-polymorph is prepared as a black solid from ditechnetium(III) tetraacetate dichloride and hydrogen chloride at 300 °C.
It has a bioctahedral structure, consisting of triangular Tc3Cl9 units with C3v 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.
[1] β-TcCl3 is obtained by the reaction between technetium metal and chlorine gas.
Its structure consists of infinite layers of edge-sharing octahedra, similar to MoCl3 and ReCl3, with distances that also indicate metal-metal bonding.