Co-crystallisation of 4-amino pyridine with succinic acid (1:1): spectroscopic, thermal, crystal structure, DFT/HF calculation and Hirshfeld surface analysis

Slow evaporation procedure yielded the co-crystal of 4-amino pyridine:Succinic acid (1:1). Thermal (TGA/DSC), FT-IR spectroscopic and single crystal X-ray diffraction (SCXRD) studies were performed to elucidate the structure and chemical characteristics. The SCXRD investigation reveals that the crystal packing is mainly strengthen by O–H···O, O–H···N, N–H···O and comparatively weak C–H···O hydrogen bonding between the 4-amino pyridine and succinic acid and further stabilised by R23(11) ring motif and weak C–O···π and π–π interaction. The optimised parameters and Mulliken charges have been investigated using density functional theory (DFT) as well as Hartree–Fock (HF) techniques (with hybrid B3LYP/6-311++G(d, p)). The molecular electrostatic potential (MSP), frontier molecular orbitals, reactivity characteristics, and the Hirshfeld surface (HS) analysis were performed. The analysis reveals that the N–H···O, O–H···N, O–H···O and C–H···O hydrogen bond interactions are the key contributors to intermolecular stabilisation in the co-crystal.