Spectroscopic (FTIR and UV-Vis) Analysis, Supramolecular Studies, XRD Structural Characterization and Theoretical Studies of Two Flavone-Oxime Derivatives

Two flavone oxime derivatives, (E)-2-phenyl-4H-chromen-4-one O-(2-bromoallyl)oxime (C₁₈H₁₄BrNO₂) (1) and (E)-2-phenyl-4H-chromen-4-one O-benzyloxime (C₂₂H₁₇NO₂) (2), were analyzed by XRD, IR (FT-IR), and UV-Vis spectroscopies. Supramolecular studies of the two compounds revealed the existence of weak C−Br…C_g halogen bonds as well as weak C−H…O interactions in the first oxime derivative and even weaker interactions dominated by dispersion forces in the second derivative. These interactions were further analyzed by observing the Hirshfeld surfaces. To evaluate the features of the halogen interactions, molecular electrostatic studies (MEP) were performed. These studies showed positive charges on the surface of the halogen atom, demonstrating the presence of a “sigma hole”. The maximum and minimum values of the molecular electrostatic potential indicate low molecular reactivity, and difficult access of the electrophilic or nucleophilic agents to the molecule, in the case of a hypothetical reaction, is observed. Spectroscopic studies in the IR region showed similar results for the two compounds, finding specific differences in the behavior of the N−O and N=C frequencies that characterize the oxime group. UV–visible spectra of both compounds were also recorded and the electronic properties, such as HOMO, LUMO and band gap energies were measured by time-dependent DFT (TD-DFT) approach. Analysis of the interaction energies of the two compounds between pairs of neighboring molecules within a radius of 3.8 Å, using the CrystalExplorer program at the DFT/6-31G level, showed that the E_dis term essentially contributed to the total interaction energy in the process of crystal formation.