Two new metastable forms of 6-chloroquinolin-2(1H)-one: Crystal structure, Hirshfeld surfaces and spectroscopic studies

Abstract

Two new metastable crystalline forms of 6-chloroquinolin-2(1H)-one (forms II and III), which were induced by two kinds of 3D inorganic anions (ClO4- and BF4-), have been prepared and characterized in this work. We performed single-crystal diffraction, X-ray powder diffraction (XRPD), Hirshfeld surfaces, solid-state vibrational spectroscopy (IR) and thermal analysis (DSC, TGA) to these two new forms as well as the original one (form I). Form I featured with 1D chain, while form II and III featured with dimeric unit with stronger π⋯π and hydrogen bonds interactions. The 3D inorganic anions force the self-assemble behavior of 6-chloroquinolin-2(1H)-one molecules from 1D chain structure (form I) to dimeric unit (forms II and III) due to their large steric hindrance, and different anions induced different orientations for dimeric unit. These transformations lead to the increase of N–H⋯O, π⋯π, and Cl–Cl intermolecular interactions, which lead to blue shift of IR spectra in 1700–1500cm−1 region as well as luminescence peaks, while red shift of IR spectra in 650–550cm−1 region.