CHAPTER 12.1:Supramolecular Structures Based on Chalcogen–Halogen Secondary Bonds

It is well documented that halides of selenium and tellurium exhibit secondary bond‐like intermolecular interactions, and a ‘continuum of interactions’ from van der Waals forces and secondary n→σ* overlap via typical 3c–4e systems to 2c–2e covalent bonds has been documented in a range of compounds. Towards the heavier halogens, chalcogen atoms can act as donors (Lewis bases) or as acceptors (Lewis acids) that can be distinguished by the coordination geometry of their adducts, since in many cases the interactions are directed in accordance with the VSEPR rules and with the concept of n(donor)→σ*(acceptor) overlap. In a number of compounds, however, selenium, tellurium, bromine, and iodine atoms appear to play the roles of donor and acceptor at the same time, so that donor–acceptor assignments and formal oxidation numbers can become arbitrary. The chapter reports a selection of supramolecular structures with chalcogen–halogen contacts, ordered under the aspects of functional groups, donor–acceptor relations, geometric implications (such as T‐shaped or square‐planar structures) and oxidation states.