Quantitative investigation of Halogen and Hydrogen bonding in 2-Chloro, 4-X-Benzoic acids

Abstract

The crystal structure, Hirshfeldsurface analysis, topological analysis of the electron density and total interaction energies of four compounds, 2-Chloro, 4-X-Benzoic Acids (where X=I, Br, Cl and F) have been analysed. The packing similarity was evaluated in all compounds using the XPac analysis. The qualitative information about intermolecular interactions is derived from the crystal structure and Hirshfeld surface analyses whereas quantitative information are determined by the QTAIM analysis as well as total interaction energies from CrystalExplorer. The topological properties are estimated for all compounds in both crystal geometry and gas phase using TOPOND and AIMALL, respectively. The carboxylic acid O-H...O HB dimers, C-H...O HBs and C sub(Pi)...C sub(Pi) aromatic stacking interactions are found to be common interactions in all compounds. The topological properties and bond paths demonstrate them as non-covalent stabilizing interactions in the crystalline state. The hierarchy of interactions concerning their strength is observed in the following order such that O-H...O HB dimers greater than C sub(Pi)...C sub(Pi) aromatic stacking interactions greater than C-H...O HBs greater than Type II X...Cl interactions and C-H...Cl HBs greater than Type I homo-halogen X...X interactions in all compounds. Additionally, the strength of Type I homo-halogen X...X interactions vary in the order: I...I greater than Br...Br greater than Cl...Cl greater than F...F. The hierarchy of interactions is further supported by molecular electrostatic potential surfaces associated with both positive and negative potential regions.