Additional stabilization of hetero-complexes of aromatic molecules: H-bonds or charge-transfer?

In this work the proof for intermolecular H-bond formation in hetero-complexes of aromatic molecules and rejection of alternative hypothesis about charge-transfer as a source of additional stabilization, reflected in experimentally-measured thermodynamical parameters of certain complexes, was provided. An empirical threshold for the relative hetero-association constant fC > 35% was suggested as an indicator of the existence of additional stabilization. It was also suggested that any new experimentally-measured hetero-association of aromatic molecules meeting this condition should be further subjected to structural analysis implying with high probability the existence of intermolecular H-bonding network.