Terahertz spectroscopic characterization and DFT calculations of vanillin cocrystals with nicotinamide and isonicotinamide

Abstract

To explore the effects of lattice vibration and molecular interaction on their formation and structure, as well as their mechanical properties, vanillin cocrystals with nicotinamide and isonicotinamide were synthesized and characterized by time-domain Terahertz spectroscopy. The lattice vibrations of these cocrystals, as well as their individual components, were investigated using the dispersion-corrected density functional theory. The simulated terahertz spectra successfully were highly consistent with their experimental spectra. Typical intensive modes of vanillin and the cocrystals were discussed in terms of the motions of hydrogen bonds. The effect of lattice vibration on cocrystal structures was further studied to gain insights into their thermodynamic stability. Geometrical values of the computationally optimized structure were calculated using density functional theory at B3LYP/6-31(d,p) to obtain the highest occupied molecular orbitals and lowest unoccupied molecular orbitals of the cocrystal. The Hirshfeld surface and the molecular electrostatic potential were explored to study the interactions between the individual component of the cocrystals. The mechanical properties of the cocrystals were also calculated using modern quantum chemical methods. This study further highlights the consistency of computational results with crystallographic values, ensuring that the computational modeling of the cocrystals is equally important for predicting their stable geometries and applications.