DFT study of hydrogen bond bridging mode of pyridine and diazenes in water environment

Optimized geometries and vibrational spectra of pyridine (Py), pyridazine (Py1,2), pyrimidine (Py1,3), pyrazine (Py1,4) and their complexes with water molecules have been calculated with a view to look into the strength of hydrogen bonds, binding energies and vibrational wavenumbers of hydrogen bond bridging modes. The counterpoise corrected binding energies for different complexes are also calculated. The results of DFT calculations have been used to draw the potential energy curve and to calculate the amplitude of stretching vibration of hydrogen bond bridging modes. The three types of hydrogen bonds: N…HO, O…HO, and O…HC have been studied. The relative hydrogen bond strengths and vibrational wavenumbers of these bridging modes have been explained in terms of redistribution of electronic charges on individual atoms.