First-Principles Prediction of Novel Technetium(IV) Halide Polymeric Compounds

We report the crystal structures of novel technetium tetrahalide polymeric compounds, TcX$_4$ [X=F,Br,I], as predicted from first-principles calculations. Similar to TcCl$_4$, TcF$_4$ and TcBr$_4$ compounds are orthorhombic with the centro-symmetric space group $Pbca$, while TcI$_4$ crystallizes in the space group $P2_1/c$. The structures consist of distorted octahedral groups of composition TcX$_6$ linked into endless linear chains. A possible explanation for the differences between these structures is offered in terms of varying degree of bonding withing the polymeric chains.