Theoretical studies of molecular structure and vibrational spectra of free, H-bonded and coordinated nicotinamide

Two H-bonded complexes resulting from the interaction between the nicotinamide (NA) conformers (E and Z) with two DMF molecules (1 and 2) respectively together with the coordination complex [Zn(NA)2(Cl)2], 3; have been calculated using DFT (B3LYP/6-311++G(d,p)) methods. The results of the calculations indicate an increase in the planarity of the NA molecule due to H-bonding interaction. Further deviation from the planarity is predicted due to the coordination of the metal ion to the NA molecule. The vibrational frequencies and infrared intensities were calculated at the same level of theory and the vibrational modes were characterized based on their potential energy distribution (PED%). The changes in the vibrational frequencies and infrared intensities showed red shifts in stretching frequencies of the amino and carbonyl groups (υNH and υCO) with increase in their vibrational intensity. The coordination of the zinc(II) ion through the pyridine nitrogen of the NA molecule leads to blue shift in the ring breathing and ring stretching modes.