Technetium(IV) Halides Predicted from First-Principles

We report the crystal structures of the novel technetium tetrahalides TcX4 [X = F, I], as predicted from first-principles calculations. Isomorphous with TcCl4 and TcBr4 crystals, TcF4 is orthorhombic with the centro-symmetric space group Pbca, while TcI4 crystallizes in the monoclinic space group P21/c. The structures, [TcX2(μ-X)4/2]∞, consist of distorted edge-sharing octahedral groups of composition TcX6 linked into endless cis chains. A possible explanation for the differences between these structures is offered in terms of varying degrees of bonding within the chains.