An investigation into the substituent effect of halogen atoms on the crystal structures of indole-3-carboxylic acid (ICA)

Abstract

An investigation into the substituent effect of halogen atoms (F, Cl, Br) on the crystal structure of indole-3-carboxylic acid (ICA) was prepared in this work. The investigation was done through the aspect of crystal structure, intermolecular interactions and π⋯π stacking motifs with the assistance of infrared spectra, elemental analyses, NMR spectra, differential scanning calorimetry (DSC), thermogravimetric analyses (TGA) and hot stage microscopy (HSM) measurements. The results revealed that the different kinds of halogen atoms and the different substituted positions have a significant effect on the crystal structures, molecular π⋯π stacking motifs and the kinds of intermolecular interactions. We further correlated the melting points of the ICAs with the H–H, O–H and X–H (X = F, Cl, Br) interactions, and found a positive correlation between them.