Intermolecular interactions on the crystal packing of 1,6-bis(pyrimidin-2-ylthio)hexane: Spectroscopic and theoretical investigation

The crystal data of 1,6-bis(pyrimidin-2-ylthio)hexane (PTH) show that this molecule crystallized in monoclinic space group P21/c and in the half part of the molecule is located the inversion center (1¯) of the structure. The crystal packing is stabilized by very weak hydrogen bonds (C2-H2⋯N2) and van der Waals interactions (S⋯S). These interactions give rise to a two-dimensional (2-D) array parallel to bc plane, where the C⋯N interactions form a wave design along the b crystallographic axis and the S⋯S are located parallel to the same axis. The C-H⋯π interaction is observed between 2-D arrays, giving rise to a three-dimensional design. Ab initio electronic structure calculations under periodic boundary conditions were performed in order to predict vibrational and electronic properties. The vibrational analysis was used to assist the assignments of the Raman and infrared bands. The solid structure was optimized and characterized as a minimum in the potential energy surface. The analysis of the density of the PTH states gives an energy gap of 2.92 eV with a significant contribution of nitrogen 2p and sulphur 3p states for valence and conduction bands. The experimental value obtained by diffuse reflectance is about 3.40 eV, indicating a good agreement between theoretical and experimental data.