Why halogen bonds are more linear than hydrogen bonds

What is it about?

Halogen bonds appear superficially similar to hydrogen bonds, but a series of experiments have shown that halogen bonds tend to be more linear than analogous hydrogen bonds. This investigation confirms these trends using high-accuracy quantum chemistry and provides some insights into the reasons why.

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Why is it important?

Halogen bonding is a hot-topic in many fields, hence a better understanding of the underlying mechanism will be important in advancing its use. We also show that for complexes of up to 10-15 atoms, the quantum chemical method chosen [CCSD(T)-F12b] produces excellent agreement with experiment - meaning it can be used for hypothetical structures or those which pose experimental difficulties. Finally, the data could also be used in benchmarking other, more efficient, computational methods.