Tuning seleniumiodine contacts: from secondary soft–soft interactions to covalent bonds

Selenium to iodine contacts ranging from the sum of the Se and I van der Waals distances to strong covalent bonds are reviewed with the help of recent structural determinations of compounds exhibiting SeI distances from 384 to 244 pm, with emphasis on ‘less clear-cut’ cases, in terms of different extents of ‘hypervalent’ 3c–4e (10-Se-3) and (10-I-2) interactions. Within a continuum of SeI interactions from undisturbed single bonds via n->σ*(SeI) interactions and typical 3c–4e XSeI or SeIX systems to van der Waals contacts, any desired SeI distances can be tuned by an appropriate choice of the particular substituents and ligands attached to the SeI moiety.