A Theoretical and Experimental Study on Hydrogen-bonding Interactions between 4H-1,2,4-triazole-3,5-diamine and DMSO/water

In this paper, 4TZDA-DMSO/water complexes formed by hydrogen bonding interactions were investigated by a combined experimental and computational approach. Two conformations of 4TZDA molecule were considered. Seven hydrogen-bonded 4TZDA-DMSO/H 2 O complexes were characterized in terms of geometries, energies and vibrational frequencies. The optimizations and calculations were performed for the complexes by Density Functional Theory. In the experimental part, the DMSO/H 2 O solutions of 4TZDA were prepared and infrared spectra of the solutions were recorded. After the solvation process, significant shifts in the existing bands and new band rising were observed in the experimental spectra of 4TZDA. Following results are found from this study: 1) 4TZDA (I) is more stable than 4TZDA (II). 2) Seven 4TZDA-DMSO and 4TZDA-H 2 O complexes are investigated and it is seen that all nitrogen atoms of 4TZDA are hydrogen bond acceptor and all hydrogen atoms are hydrogen bond donors. 3) Aqueous complexes of 4TZDA are found to form stronger hydrogen bonds compared to DMSO complexes. 4) It is determined that the most stable structures are intermolecular interactions of lpO⋯H-N and lpN⋯H-O type for the complexes. For these interactions, h-bond lengths are calculated as 1.78 and 1.90 A and interaction energies are -7.10 kJ/mol for 4TZDA-DMSO and -50.5 kJ/mol for 4TZDA-H 2 O. Because of this energy difference in the complexes, it can be said 4TZDA forms more stable complexes with water molecules compared to DMSO molecules and with this property, it is an ideal molecule for pharmacological purposes.