OH stretching vibrations and hydrogen-bonded structures of 7-hydroxyquinoline-(H2O)1–3 investigated by IR–UV double-resonance spectroscopy

Hydrogen(H)-bonded structures of 7-hydroxyquinoline-(H2O)n clusters were investigated based on the analysis of the infrared spectra of the OH stretching vibrations in combination with ab initio calculations. For 7-hydroxyquinoline-(H2O)1, two isomers due to different H-bonding sites were found to coexist; in one of them 7-hydroxyquinoline acts as a proton donor, and in the other the OH group of water is H-bonded to the nitrogen site of 7-hydroxyquinoline. For 7-hydroxyquinoline-(H2O)2–3, the structures were determined to be bridge forms, in which a linear-form water cluster is H-bonded to the OH hydrogen and to the nitrogen of 7-hydroxyquinoline.