Structure of hydrated clusters of dibenzo-18-crown-6-ether in a supersonic jet—encapsulation of water molecules in the crown cavity

Abstract

The structure of dibenzo-18-crown-6-ether (DB18C6) and its hydrated clusters has been investigated in a supersonic jet. Two conformers of bare DB18C6 and six hydrated clusters (DB18C6–(H₂O)_n) were identified by laser-induced fluorescence, fluorescence-detected UV–UV hole-burning and IR–UV double-resonance spectroscopy. The IR–UV double resonance spectra were compared with the IR spectra obtained by quantum chemical calculations at the B3LYP/6-31+G* level. The two conformers of bare DB18C6 are assigned to “boat” and “chair I” forms, respectively, among which the boat form is dominant. All the six DB18C6–(H₂O)_nclusters with n = 1–4 have a boat conformation in the DB18C6 part. The water molecules form a variety of hydration networks in the boat–DB18C6 cavity. In DB18C6–(H₂O)₁, a water molecule forms the bidentate hydrogen bond with the O atoms adjacent to the benzene rings. In this cluster, the water molecule is preferentially hydrogen bonded from the bottom of boat–DB18C6. In the larger clusters, the hydration networks are developed on the basis of the DB18C6–(H₂O)₁cluster.