Experimental and density functional studies on 4-(2,3-dichlorobenzylideneamino)antipyrine and 4-(2,5-dichlorobenzylideneamino)antipyrine

Two antipyrine derivates, both with formula C18H15Cl2N3O, are structurally similar Schiff bases derived from the condensation of 2,3-dichlorobenzaldehyde or 2,5-dichlorbenzaldehyde with 4-aminoantipyrine in methanol solution. The compounds were characterized by elemental analysis, FT-IR, FT-Raman, UV–vis and X-ray single crystal diffraction techniques. As expected, both compounds adopt trans configurations about the Schiff base imine CN bonds. Density functional calculations were performed to further optimize and characterize them. The results indicate that the theoretical values show good agreement with experimental ones. The thermodynamic functions (standard heat capacities, standard entropies and standard enthalpy changes) and their correlations with temperatures have been obtained from their theoretical harmonic frequencies of the optimized structures. The intramolecular electronic transfer and nonlinear optical properties of the compounds can be explained clearly by the molecular frontier orbitals and pi-electron systems.