Synthesis and structural studies on the supramolecular architecture of two novel proton transfer molecular salts of 2-aminopyridine

Herein, synthesis, analytical and structural characterization of two new molecular salts (AP -PHBA and AP -NA) of 2 -aminopyridine (AP) using GRAS molecules i.e, p -hydroxybenzoic acid (PHBA) and nicotinic acid (NA) has been envisaged. The TGA/DSC revealed that both molecular salts were thermally more stable than the AP molecule. In the UV-Vis spectrum of AP -PHBA there observed a bathochromic shift (lambda(max) 298 nm to 305 nm) caused by extended conjugation due to the hydroxy group at the para position of PHBA which might influence the photophysical property and no such shift was observed in AP -NA (lambda(max) = 298 nm). Both the salts were found to be dominated by the two -point charge assisted acid -pyridine heterosynthonic ring motif with graph set notation R- 2(2) (8). This was held via N (+) -H ...O - and N -H ...O linkages that formed between the 2 -aminopyridinium cation and carboxylate anions. In both crystals, a ribbon synthon linking the ring synthon via N2 A -H2 AB / AC...O3 B hydrogen bonds was noted with the chain motifs C- 2(1) (6) and C- 2(2) (6). Furthermore, the C1 A -H1 AA ...N1 B and N2 A -H2 AC ...O3 B networks were associated to build a large tetramer with R 44 (22) was seen in the AP -NA salt system. From Hirshfeld surfaces analysis, it was noteworthy that the variation in the percentage contribution of O ...H (20.8% in AP -PHBA and 15.8% in AP -NA) and N ...H (1.9% in AP -PHBA and 12.1% in AP -NA) interconnects signify the importance of hydroxy group (PHBA) and pyridine N (NA) in stabilizing the crystal systems. Hence, a complete analysis of crystal structure and supramolecular packing of the two molecular salts AP -PHBA and AP -NA was presented. (C) 2022 Elsevier B.V. All rights reserved

Automated summary

In this study, two new molecular salts (AP-PHBA and AP-NA) of 2-aminopyridine (AP) were synthesized using p-hydroxybenzoic acid (PHBA) and nicotinic acid (NA) as the GRAS molecules. The thermal stability of both salts was found to be higher than that of the AP molecule. The UV-Vis spectrum analysis showed a bathochromic shift in AP-PHBA due to the extended conjugation caused by the hydroxy group of PHBA, while no such shift was observed in AP-NA. Both salts exhibited a two-point charge assisted acid-pyridine heterosynthonic ring motif dominated by N(+)-H...O- and N-H...O linkages. The crystal structures of the salts were characterized by ribbon and chain motifs formed by hydrogen bonding interactions. Hirshfeld surfaces analysis revealed the importance of the hydroxy group (PHBA) and pyridine N (NA) in stabilizing the crystal systems. This study provides a comprehensive analysis of the crystal structure and supramolecular packing of AP-PHBA and AP-NA salts.