Substituent effects in cation-p interactions. Recognition of tetramethylammonium chloride by uranyl-salophen receptors

The binding affinities of tetramethylammonium chloride to uranyl salophen receptors decorated with X-substituted aromatic pendants (X ¼ OCH3, CH3, H, Br, NO2) point to the importance of resonance effects in cation-p interactions, at variance with the view that field/inductive effects play a dominant role.