Molecular structure, hydrogen-bonding patterns and topological analysis (QTAIM and NCI) of 5-methoxy-2-nitroaniline and 5-methoxy-2-nitroaniline with 2-amino-5-nitropyridine (1:1) co-crystal

In this work, we report an analysis of the molecular structure and the hydrogen-bonding patterns in the crystal structures of 5-methoxy-2-nitroaniline (1) and 5-methoxy-2-nitroaniline with 2-amino-5-nitropyridine (1:1) co-crystal (2). X-ray single crystal diffraction experiments were carried out to analyse the intermolecular forces in terms of geometrical criteria. These intermolecular interactions were also investigated through topological analysis of the electron density (ρ) employing QTAIM and NCI methods. Additionally, Raman spectroscopy was employed to analyse the vibrational characteristics of the entitled materials. The supramolecular structure of (1) is produced by crosslinked chains, which are primarily dominated by N-H⋯O hydrogen bonds. However, C-H⋯O interactions reinforce this connectivity. Furthermore, the molecules in (1) are connected through two-centre instead of the three-centre hydrogen-bonding interactions between the -NH₂ and -NO₂ groups commonly observed in nitroanilines. The asymmetric unit of (2) contains two symmetry-independent molecules of 5-methoxy-2-nitroaniline (5M2NA) and two symmetry-independent molecules of 2-amino-5-nitropyridine (2A5NP). The supramolecular structure of (2) is developed not only for N-H⋯O but also N-H⋯N and supportive C-H⋯O hydrogen bonds. The two symmetry-independent 2A5NP molecules bound to each other through two-centre hydrogen bonds between the -NH₂ and -NO₂ groups forming C22(16) chains. 5M2NA molecules bound to these chains forming R229 and R22(8) synthons. Experimental and theoretical results obtained in this work suggest that C-H⋯O interactions play an important role in the stabilization of these supramolecular structures.