On the structures of free-base lepidine and some mineral acid salts *

The crystal and molecular structures of free-base lepidine (4-methylquinoline, 1) and the mineral acid salts lepidinium chloride (2), nitrate (3) and dihydrogen phosphate (4) are reported. Compound 1 was studied by differential scanning calorimetry and in situ capillary cryocrystallography. In the crystal struc-tures, the molecules of free-base lepidine in 1 and the lepidinium cations in 2 -4 are face-to-face 7r center dot center dot center dot 7r- stacked. The quinoline nitrogen atom is not involved in directional intermolecular interactions such as weak hydrogen bonds in 1. In the salts 2 -4, proton transfer to the quinoline nitrogen atom and N -H center dot center dot center dot Cl (in 2) and N -H center dot center dot center dot O (in 3 and 4) hydrogen bonding is observed. Hirshfeld surface analysis reveals that lepidinium salts 2 and 3 form hydrogen-bonded dimers in the crystal and confirms that the packing of 4 is dominated by hydrogen-bonded dihydrogen phosphate anion chains.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

The crystal and molecular structures of free-base lepidine and its mineral acid salts have been investigated. The stacking arrangement of the molecules and cations were elucidated, as well as the involvement of nitrogen atoms in intermolecular interactions. Hydrogen bonding between the salts and lepidinium cations was observed. Hirshfeld surface analysis provided insights into the packing arrangements of the salts.