Study of molecular structure and hydrogen bond interactions in dipfluzine-benzoic acid (DIP-BEN) cocrystal using spectroscopic and quantum chemical method.

The purpose of this article is to predict the molecular structure of the cocrystal of dipfluzine-benzoic acid (DIP-BEN) through computational approach (DFT calculations) and validate it using vibrational spectroscopic studies. The molecular structure of the DIP-BEN cocrystal has been predicted by forming models on the basis of the active sites available to form H-bonds between dipfluzine (DIP) and benzoic acid (BEN). Conformational study has been performed and potential energy surface scans are plotted around the flexible bonds of the cocrystal molecule and three stable conformers have been obtained. Quantum theory of atoms in molecules (QTAIM) explains that all the interactions are medium and partially covalent in nature. Natural bond orbital analysis of the second order perturbation theory of the Fock matrix suggests that interactions LP (2) O2 → σ*(O74H75) and LP (2) F1 → σ* (O89H90) are responsible for the stabilization of the molecule. The HOMO and LUMO energies and electronic charge transfer (ECT) confirms that charge flows from BEN to DIP. Global reactivity descriptor parameters suggest that DIP-BEN cocrystal is softer, thus more reactive in comparison to DIP. Local reactivity descriptor parameter is used to predict reactive sites of the cocrystal. The experimental and theoretical results support the formation of cocrystal through strong hydrogen bond (O89H90⋯F1 and O74H75⋯O2) interactions present in cocrystal.