Conclusions
The lysine amino acid was cocrystallized with an important antiseptic agent mandelic acid. Single crystal X-ray analysis revealed that there was a proton transfer from the carboxylic acid group of mandelic acid to the lysine side chain and lysine also exhibits a zwitterionic form due to the proton transfer from the carboxylic acid of lysine to the backbone amino group. The inclusion of water molecules in the crystal lattice facilitates the formation of intermolecular N–H···O and O–H···O interactions. The strength and stabilizing/destabilizing nature of different dimeric complexes were evaluated by the PIXEL energy analysis. The relative contribution of different inter-contacts was qualitatively analyzed using Hirshfeld surface analysis and 2D fingerprint plots. Topological analysis suggested that N–H+···O- interactions which emanated from proton transfer between the side chain N2 of lysine and the carboxylate of the mandelate and between atom backbone N1 and the carboxylate group of lysine showed intermediate bonding character between closed and shared shell interactions. Other interactions that exist in the title complex are closed shell in nature.