Experimental and density functional studies on 4-(3,4-dihydroxybenzylideneamino)antipyrine, and 4-(2,3,4-trihydroxybenzylideneamino)antipyrine

Two antipyrine derivates, 4-(3,4-dihydroxybenzylideneamino)antipyrine (DHBAP), and 4-(2,3,4-trihydroxybenzylideneamino)antipyrine (THBAP), are structurally similar Schiff bases derived from the condensation of 3,4-dihydroxybenzaldehyde and 2,3,4-trihydroxybenzaldehyde with 4-aminoantipyrine in methanol solutions. The compounds were characterized by elemental analysis, FT-IR and UV-vis techniques. Density functional calculations were carried out to further optimize and to characterize them. The calculated results show that the optimized geometries can well reproduce the crystal structures and the theoretical vibrational frequencies show good agreement with experimental ones. The statistical thermodynamic properties (standard heat capacities, standard entropies, and standard enthalpy changes) and their correlations with temperature have been obtained from the theoretical vibrations. The theoretical electronic transitions (ET) are mainly assigned to the corresponding frontier molecular orbitals to respond to the experimental UV-vis absorption spectra. The predicted nonlinear optical (NLO) properties of DHBAP and THBAP are much greater than ones of urea. The ET and NLO properties are caused by the molecular frontier orbitals and pi-electron conjugative effect.