Theoretical analysis of hydrogen bonding in catechol-n(H(2)O) clusters (n = 0...3)

The electronic structure and hydrogen bonding of the stable isomers of catechol and its complexes with one to three water molecules is studied by means of theoretical methods. A conformational analysis based on a simulated annealing search on the potential energy surface of each complex was carried out previous to the quantum chemical energy minimization. Twenty three stable conformers were found including some involving a pi-interaction between the catechol moiety and a water molecule. The topological properties of the electron density reveal the presence of an intramolecular hydrogen bond only in the case of one complex with three water molecules. The infrared spectra of these molecules were computed and compared to available experimental results. An alternative assignment of the experimental vibrational spectrum within the range 3340-3750 cm(-1) of the catechol-3(H(2)O) complex (M. Gerhards, C. Unterberg, and K. Kleinermanns, Phys. Chem. Chem. Phys. 2000, 2, p. 5538) is proposed. The red-shift observed for the stretching vibrational frequency of the catechol hydrogen donor hydroxyl group in the presence of water molecules is rationalized in terms of the properties of the electron distribution and a Darwinian family tree is proposed to classify the diverse structural and energetic characteristics of the stable complexes found.