2-Propylamino-5-[4-(2-hydroxy-3,5-dichlorobenzylideneamino) phenyl]-1,3,4-thiadiazole: X-ray and DFT-calculated structures

2-Propylamino-5-4-(2-hydroxy-3,5-dichlorobenzylideneamino) phenyl]-1,3,4-thiadiazole, formulated as C₁₈H₁₆Cl₂N₄OS (I), was synthesized. The crystal and molecular structure of (I) have been determined by ¹H-NMR, IR, and X-ray single crystal diffraction. The compound (I) crystallizes in the monoclinic, space group P2(1)/c with unit cell parameters a = 9.0576(2) Å, b = 24.3382(8) Å, c = 9.0585(2) Å, M _r = 407.31, V = 1851.13(9) Å³, Z = 4, R ₁ = 0.036, and wR ₂ = 0.096. Molecular geometry from X-ray experiment of (I) in the ground state has been compared using the density functional method (B3LYP) with 6-31G(d) basis set. To determine conformational flexibility, molecular energy profile of (I) was obtained by semi-empirical (PM3) calculations with respect to selected degree of torsional freedom, which was varied from ?180° to +180° in steps of 10°. The results are indicative that the Schiff base, which contains a thiadiazole ring, prefers to be in E-configuration. In addition, molecular electrostatic potential, frontier molecular orbitals, and natural bond orbitals analysis were performed by the B3LYP/6-31G(d) method.