Vibrational spectra and structure of methyl-derivatives of imidazo[4,5-c]pyridine based on DFT quantum chemical calculations and XRD studies

The molecular structures, vibrational energy levels and potential energy distribution of 4-methyl-imidazo[4,5-c]pyridine (4MIPc) and 7-methyl-imidazo[4,5-c]pyridine (7MIPc) are derived from the quantum chemical calculations and compared to the experimental results obtained from the X-ray diffraction (XRD), IR and Raman studies. The B3LYP/6-311G(2d,2p) quantum model and PED contributions have been applied for the assignment of the vibrational modes. 4MIPc crystallizes in an orthorhombic structure, space group Pna21 and Z = 4 and 7MIPc crystallizes in a triclinic structure, space group P−1 and Z = 4. The almost planar conformation of the molecules and presence of the N–H⋯N hydrogen bonds formed with the pyridine and imidazole nitrogen atoms was found to be characteristic for the studied systems. The presence of hydrogen bonds is also confirmed by the results of IR studies.