Interplay of weak noncovalent interactions in two conjugated positional isomers: A combined X-ray, optical properties and theoretical investigation

Abstract Two conjugated positional isomers {(2Z,2′Z)-3,3'-(1,4-phenylene)bis (2-(pyridin-2-yl)acrylonitrile), I and (2Z,2′Z)-2,2'-(1,4-phenylene)bis (3-(pyridin-2-yl)acrylonitrile), II} in which –CN group is attached to either first or second carbon atom of the C C unit, have been synthesized. One of the isomers I crystallized as a hydrated form. Single crystal X-ray analysis has been performed and a detailed quantitative analysis on the weak noncovalent interactions was presented. The results suggest that these three molecules showed different crystal packing. The positioning of the –CN group at different carbon atom of the C C unit in the isomers and the presence of a water molecule in the crystal lattice alters the distribution of electrostatic potentials. Lattice energy calculation revealed that a water molecule destabilizes the isomer I by 20.5 kcal mol −1 and the isomer II was found to be more stable. The energy frameworks displayed hexagonal packing for isomers I and II, but the variation in the magnitude of electrostatic and dispersion energies and the arrangement of molecules in the crystalline state. The Hirshfeld surface and QTAIM approaches were used to study the nature and the extent of different intermolecular interactions observed in these structures. The results indicated that intermolecular C–H⋯N interactions play a significant role in the stabilization and H–H bonding was also substantially contributing to the stabilization. UV–Vis spectral data were reported for I and II in solution and solid phases and showed similar optical properties.