2D-3D Supramolecular Assemblies Containing 2-Amino-4,6-dimethoxypyrimidine and Carboxylic Acids: Preparation, Crystallographic Characterization, and Hirshfeld Surface Analysis

Eight crystals (1-8) derived from various substituted carboxylic acids of 2-pyrazinecarboxylic acid, 3,4-methylenedioxybenzoic acid, 4-hydroxy-3-nitrobenzoic acid, 4-chloro-2-nitrobenzoic acid, mandelic acid, 4-nitrophenylacetic acid, 3,4,5-trimethoxycinnamic acid, and itaconic acid and 2-amino-4,6-dimethoxypyrimidine (admpm) were prepared and identified, and further characterized thoroughly with single crystal X-ray diffraction (SCXRD), and elemental analysis techniques. The melting points were also measured. Significant non-covalent interactions were calculated by means of the Hirshfeld surface analysis. Among the eight crystals, proton transfer from the carboxylic acid to ring N of the pyrimidine has occurred only at 1, while the remaining ones 2-8 were co-crystals. It is obvious that the R22(8) ring motif occurs in all cases when a carboxyl unit interacts with a pyrimidine base. The present work surely indicates that there are two main associate modes between the 2amino-4,6-dimethoxypyrimidine and the carboxylic acids, which regularly occur, linear heterotetramer (LHT), and cyclic heterotetramer (CHT). Here, LHT is dominant as it occurs in 5/8 frequency (at 3-4 and 6-8), CHT in 2/8 (at 1-2), with the remaining one structure (5) forming a heterodimer. The heterotrimer (HT) was not established in this test. Thus LHT is more stable than CHT and other synthons.