Quantitative investigations of intermolecular interactions in 2-amino-3-nitropyridine polymorphs: Inputs from quantum mechanical calculations

Two polymorphic forms (Form–I and Form–II) of 2-amino-3-nitropyridine are structurally characterized by single crystal X-ray diffraction analysis and compared with another polymorphic form (Form–III, retrieved from CSD) with a detailed analysis of the Hirshfeld surfaces and fingerprint plots facilitating a comparison of intermolecular interactions. X-ray crystallography exposes that the polymorphs generate completely different network structures through hydrogen bonding interactions. Polymorphic Form–I exhibit a layer assembly through the cooperative face-to-face π⋯π and lone pair⋯π interactions, whereas Form–II, and Form–III displays hydrogen bonds only. A detailed investigation of Hirshfeld surface analysis reveals much more detailed scrutiny of intermolecular interactions experienced by the polymorphic forms of 2-amino-3-nitropyridine. The quantitative analysis of the interaction energies involving various noncovalent interactions was computed and compared to get a deeper insight into the role of such interactions in stabilizing the polymorphs. The interaction energies of non-covalent interactions are calculated through theoretical DFT calculations as well as the PIXEL method. The PIXEL method provides us precise interaction energy calculation with an energy decomposition scheme. Higher electrostatic interaction shows higher interaction energy while the lower interaction energy corresponds to the higher dispersive interaction. The lattice energies of the polymorphs are also obtained via the PIXEL method. The nature and strength of these interactions have been studied using Bader's quantum theory of atoms in molecules. The topological analysis unequivocally establishes the presence of (3, −1) bond critical point, suggesting that the intermolecular interactions are closed-shell interactions. The NCI (Non-covalent Interaction) plots are further employed to identify and characterize the non-covalent interactions of the polymorphs.