Continuum of covalent to intermolecular bonding in the halogen-bonded complexes of 1,4-diazabicyclo[2.2.2]octane with bromine-containing electrophiles.

A gradual change of BrN bond lengths and strengths from the values typical for intermolecular associates to that characteristic of a covalent bond was observed in a series of halogen-bonded complexes. This continuum reveals a fundamental relationship between the limiting types of bonding and implies the onset of covalency in the intermolecular interactions.