Monitoring the 1160 cm(-1) band of pyridazine to investigate complexes with formamide

Hydrogen bonding between pyridazine (PRD) and formamide (FA) molecules has been investigated both experimentally by Raman spectroscopy on their binary mixtures and theoretically by DFT calculations on various gas-phase PRD:FA clusters. The band at 1160 cm(-1) of PRD was used for the first time as a marker for monitoring the degree of complexation. Upon dilution with FA, a new band at 1169 cm(-1) is observed and attributed to hydrogen-bonded PRO. The Raman experiments were complemented by OFT calculations and the corresponding structures, vibrational spectra and binding energies were determined. The most stable species were found to be the 1:2 PRD:FA complexes and such stoichiometry is in excellent agreement with the experimental determination. The shift to higher frequency observed to the prominent modes of PRO may be related to a shortening of the NC and CC bonds, upon complexation, which causes a decrease in the electron delocalization in PRO ring. (C) 2010 Elsevier B.V. All rights reserved. (AU)