Horning-crown diamine complexes and salts: proton transfer mediated by solid-state intermolecular hydrogen bonding

Horning-crown macrocycles form sheath/core inclusion complexes or salts with alkyldiamines. The degree of proton transfer appears to be mediated by intermolecular hydrogen bonding interactions. Among seven crystal structures examined, neutral complexes, hemi-salts and salts were revealed. With crystalline materials, the extent of proton transfer appeared to reflect the degree of stabilisation of phenolates and ammonium groups by hydrogen bond donors and acceptors rather than merely differences in solution phase pK(a).