Structure and hydrogen bonding of 2-aminopyridine·(H2O)n (n = 1, 2) studied by infrared ion depletion spectroscopy

Abstract

The electronic and vibrational spectra of the clusters of 2-aminopyridine (2AP) with one and two water molecules have been measured by using resonant two-photon ionization (R2PI) and IR predissociation spectroscopy (IR/R2PI). Under microhydration the aromatic nitrogen forms a very strong hydrogen bond with water. The H-bonded OH stretching vibrations for 2AP·H₂O and 2AP·(H₂O)₂ exhibit a red shift of 254 and 413 cm⁻¹, respectively, relative to the symmetric stretching vibration of free water. In addition water forms an H-bond with the amino group, resulting in a cyclic structure for both clusters. However, due to a reduced geometrical strain, the 2AP·(H₂O)₂ cluster exhibits considerably stronger H-bonds than the 2AP·H₂O cluster. The results of calculations performed both at the density functional and perturbation level of theory are also reported. Theoretical results are in good agreement with the experimental data. In addition, they bring further insight into the structure and energetics of the microhydrated molecule.