Interplay of weak intermolecular interactions in two Schiff's bases with organic fluorine derived from 5-nitrothiophene-2-carboxaldehyde: Crystal structures, DFT calculation and in vitro evaluation of bioactivities

Crystal structures of two newly synthesized Schiff's bases with organic fluorine {systematic name: (E)-N-(4-Fluorophenyl)-1-(5-nitrothiophen-2-yl)methanimine (1) and (E)-N-(2-trifluorophenyl)-1-(5-nitrothiophen-2-yl)methanimine (2)} are reported. In this contribution, we performed a qualitative analysis of intermolecular interactions using the Hirshfeld surface and 2D-fingerprint plots to understand the effect of -F and -CF3 substituents. Compounds 1 and 2 and their respective isomers, -F in the meta and -CF3 in para position on the phenyl ring, are analyzed and compared. This analysis suggests that three C-H center dot center dot center dot O, one C-H center dot center dot center dot F and a short S1 center dot center dot center dot C4 interactions found to be important for stabilization of crystal structure 1 and three C-H center dot center dot center dot O, one C-H center dot center dot center dot F, one C-F center dot center dot center dot pi halogen bond and pi center dot center dot center dot pi interactions are found to be vital for stabilization of crystal structure 2. Further, intermolecular interaction energies of molecular dimers in 1 and 2 are obtained using PIXEL energy analysis. The lattice energies for structures 1, 2 and their isomers are calculated. The energetic analysis suggests that structure 2 is more stable than its para isomer and 1. Structure 1 and its meta isomer show 1D structural similarity. The quantitative analysis of intermolecular interactions involved in the molecular dimers of 1, 2 and selected dimers of meta isomer of 1 using Bader's quantum theory of atoms-in-molecules approach. An in vitro evaluation of antimicrobial activities reveals that compounds 1 and 2 exhibit potent and broad spectrum antibacterial activity against selected Gram-positive and Gram-negative bacterial stains. (C) 2020 Elsevier B.V. All rights reserved.