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.

采用缓慢挥发法制备得到4-氨基吡啶(4-amino pyridine)与琥珀酸(Succinic acid)按1:1摩尔比形成的共晶体。为阐明该共晶体的结构与化学特性，本研究开展了热重-差示扫描量热法(TGA/DSC)、傅里叶变换红外(FT-IR)光谱及单晶X射线衍射(Single Crystal X-ray Diffraction, SCXRD)表征分析。单晶X射线衍射分析结果显示，4-氨基吡啶与琥珀酸分子间主要通过O–H···O、O–H···N、N–H···O以及相对较弱的C–H···O氢键作用强化晶体堆积结构，并通过R₂₃(11)环基序、弱C–O···π与π–π堆积作用进一步稳定晶体结构。本研究采用密度泛函理论(Density Functional Theory, DFT)与哈特里-福克(Hartree–Fock, HF)方法（结合杂化B3LYP泛函及6-311++G(d,p)基组），对该共晶体的优化结构参数与茂利肯电荷(Mulliken charges)进行了计算分析。此外还开展了分子静电势(Molecular Electrostatic Potential, MSP)、前线分子轨道、反应活性特征以及赫希菲尔德表面(Hirshfeld Surface, HS)分析。最终分析结果表明，N–H···O、O–H···N、O–H···O与C–H···O氢键相互作用是该共晶体分子间稳定作用的核心贡献因素。