MATRIX-ISOLATION STUDIES AND ABINITIO CALCULATIONS OF THE VIBRATIONAL-SPECTRA OF COMPLEXES OF WATER WITH 3-HYDROXYPYRIDINE

Experimental infrared spectra of a mixture of 3-hydroxypyridine and water in an argon matrix formed by condensation of a gaseous mixture onto a cold window at 15 K exhibit new bands from the two types of 1:1 complexes formed between the two molecules. The first of these is H2O...HO(3HP), in which the water molecule acts as a proton acceptor from the OH group of the 3-hydroxypyridine, while the second is HOH...N(3HP), with the water molecule acting as a proton donor to the N atom of the 3-hydroxypyridine. The vibrational spectra of these complexes are recorded and compared with the spectra of the isolated H2O and 3-hydroxypyridine molecules to observe the changes that result from complex formation. The relative concentrations of each complex are estimated from the observed relative intensities and the calculated values of the absolute intensities of the corresponding bands. In order to verify these experimental observations and to aid in their interpretation, ab initio calculations at the HF/6-31G(d) level have been carried out to predict the infrared spectra of the monomers and of the complexes. In general, there is good agreement between the experimental and calculated spectra. The calculations provide a basis for the assignment of the experimental spectra of the monomer and for both complexes. According to the calculations the intramolecular vibrations of the 3-hydroxypyridine do not change appreciably on complex formation, except for those bonds directly involved in the hydrogen bonding. Analysis of the calculated changes in terms of changes in the intensity parameters and in the force constants for the OH stretching mode (for the proton donor group in the hydrogen bond) shows striking similarities for the two complexes studied here and the water dimer.