π–π Noncovalent Interaction Involving 1,2,4- and 1,3,4-Oxadiazole Systems: The Combined Experimental, Theoretical, and Database Study

Abstract

A series of <i>N</i>-pyridyl ureas bearing 1,2,4- (<b>1a</b>, <b>2a</b>, and <b>3a</b>) and 1,3,4-oxadiazole moiety (<b>1b</b>, <b>2b</b>, <b>3b</b>) was prepared and characterized by HRMS, ¹H and ¹³C NMR spectroscopy, as well as X-ray diffraction. The inspection of the crystal structures of (<b>1</b>-<b>3</b>)<b>a</b>,<b>b</b> and the Hirshfeld surface analysis made possible the recognition of the (oxadiazole)···(pyridine) and (oxadiazole)···(oxadiazole) interactions. The presence of these interactions was confirmed theoretically by DFT calculations, including NCI analysis for experimentally determined crystal structures as well as QTAIM analysis for optimized equilibrium structures. The preformed database survey allowed the verification of additional examples of relevant (oxadiazole)···π interactions both in Cambridge Structural Database and in Protein Data Bank, including the cocrystal of commercial anti-HIV drug Raltegravir.