Experimental and theoretical analysis of lp•••π intermolecular interactions in derivatives of 1,2,4-triazoles

In the present study, we have synthesized and characterized two biologically active 1,2,4-triazole derivatives, a fluoro derivative, namely (E)-3-(4-fluoro-3-phenoxyphenyl)-4-((4-fluorobenzylidene)amino)1-(morpholinomethyl)-1H-1,2,4-triazole-5(4H)-thione (TRZ-1), and a chloro derivative, namely (E)-4-((4chlorobenzylidene)amino)-3-(4-fluoro-3-phenoxyphenyl)-1-(morpholinomethyl)-1H-1,2,4-triazole-5(4H)-thione (TRZ-2), via single crystal and powder X-ray diffraction. The chloro derivative crystallizes in an anhydrous form (TRZ-2A) and a solvated one (TRZ-2B) due to the presence of a toluene molecule in the crystal. This solvatomorphic behavior has been studied in detail using different thermal techniques, namely DSC and TGA, combined with hot stage microscopy (HSM). All of the three crystal structures show the presence of different intermolecular interactions of the type C-H center dot center dot center dot O,C-H center dot center dot center dot S=C,C-H center dot center dot center dot pi, C-H center dot center dot center dot X (X = -F, -Cl), pi center dot center dot center dot pi and lp center dot center dot center dot pi interactions. The fingerprints for all these interactions were evaluated using Hirshfeld surfaces. The nature and energetics associated with these interactions were characterized using PIXEL and supported by ab initio quantum mechanical calculations using TURBOMOLE. In addition, the calculations performed on the evaluation of the electrostatic potential provide deeper insights into the nature of lp center dot center dot center dot pi interactions.