Ab initio and semi-empirical computational studies on 5-hydroxy-5,6-di-pyridin-2-yl-4,5-dihidro-2H-[1,2,4]triazine-3-thione

The title compound, 5-hydroxy-5,6-di-pyridin-2-yl-4,5-dihidro-2H-[1,2,4]triazine-3-thione (C13H11N5OS), was prepared and characterized by electronic spectroscopy and single-crystal X-ray diffraction (XRD). The compound crystallizes in the triclinic space group P-1 with a = 8.5808(8) Å, b = 8.7032(7) Å, c = 10.0505(9) Å, α = 84.194(7)°, β = 75.181(7)° and γ = 63.562(6)°. In addition to the molecular geometry, vibrational frequencies and gauge including atomic orbital (GIAO) 1H and 13C NMR chemical shift values of the title compound in the ground state have been calculated using the Hartree–Fock (HF) and density functional theory (DFT) methods with 6-31G(d) basis sets. To determine conformational flexibility, the molecular energy profile of the title compound was obtained by semi-empirical (AM1) calculations with respect to the selected torsion angle, which was varied from −180° to +180° in steps of 10°. The energetic behavior of the title compound in solvent media was examined using the B3LYP method with the 6-31G(d) basis set by applying the Onsager and the Polarizable Continuum Model (PCM). By using TD-DFT method, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and the experimental one is determined. The predicted nonlinear optical properties of the title compound are much greater than ones of urea. In addition, the molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis and thermodynamic properties of the title compound were investigated using theoretical calculations.