β-Technetium Trichloride: Formation, Structure, and First-Principles Calculations

A second polymorph of technetium trichloride, β-TcCl3, has been identified from the reaction between Tc metal and Cl2 gas. The structure of β-TcCl3 consists of infinite layers of edge-sharing octahedra, similar to its MoCl3 and RuCl3 analogues. The Tc–Tc distance [2.861(3) Å] between adjacent octahedra is indicative of metal–metal bonding. Earlier theoretical work predicted that β-TcCl3 is less stable than α-TcCl3. In agreement with the prediction, β-TcCl3 slowly transforms into α-TcCl3 (Tc3Cl9) over 16 days at 280 °C.