Synthesis, crystal structure, antioxidant activity and dft study of 2-aryl-2,3-dihydro-4H-[1,3]thiazino[3,2-a]benzimidazol-4-One

The compound 2-aryl-2,3-dihydro-4H- [1,3]thiazino[3,2-a]benzimidazol-4-one (C₁₆H₁₂N₂OS) (III) was synthesized. The compound crystallized in a monoclinic crystal system with P2₁/c space group as revealed by mono-crystal X-ray diffraction. The X-ray analysis and density functional theory complementary calculations showed that noncovalent C–H···π interactions between the benzimidazole system and the thiazine ring form a dimerization along the direction of the b axes, additionally π···π interactions were found between the benzene rings. The C12, in the thiazine ring, has a distortion angle (41.69°) respect to the plane of benzimidazole. The intermolecular interactions in the crystal structure were quantified and analyzed using Hirshfeld surface analysis. The predominant interaction within the crystalline structure was found to be H⋯H interaction. On the other hand, antioxidant activity of the C₁₆H₁₂N₂OS system was studied using the DPPH[rad] and ABTS[rad]⁺ assay. Using the energy profile for the reaction of DPPH[rad] with III it was demonstrated that the antioxidant activity is carried out through HAT (H12) mechanism where conjugation of the radical can occur between the C12 of the thiazine ring and the aromatic ring, this was confirmed by a H function calculation. The importance of this study focuses on the promising range of biological activities and molecular characteristics of the synthesized compound (III).