Structural, Vibrational and UV/Vis Studies of Adamantane-Containing Triazole Thiones by Spectral, DFT and Multi-reference ab initio Methods

The Fourier transform infrared and Raman spectra of two adamantane-containing triazole thiones, namely 3-(adamantan-1-yl)-1-[(4-benzylpiperazin-1-yl)methyl]-4-phenyl-1H-1,2,4-triazole-5(4H)-thione and 3-(adamantan-1-yl)-4-phenyl-1-[(4-phenylpiperazin-1-yl)methyl]-1H-1,2,4-triazole-5(4H)-thione, were examined in the ranges of 3200–650 cm−1 and 3200–150 cm−1, respectively. The density functional theory calculations were performed for the geometric structures and vibrational spectra for the title molecules. The accurate equilibrium geometry structures of the molecules were determined on the basis of full geometry optimization at the B3LYP/cc-pVDZ level of the theory. The IR and Raman vibrational spectra were calculated and compared with the experimental ones. The experimental vibrational FT-IR and Raman spectra were interpreted. Based on the structure of the molecules the biological activity indices were predicted. It is established that compounds under consideration are very likely to exhibit the analgesic activities. The UV/Vis spectra of solution of the compounds in ethanol were measured in the range of 450–200 nm. The UV/Vis spectra simulations at the Time-Dependent DFT and Multi-Reference Perturbation Theory levels of theory demonstrate unsuitability of the TDDFT for description of the experimental spectra of the title molecules. It is highly probable that this is a consequence of the intramolecular charge transfer. In contrast, the MRPT results are in a good agreement with the experimental spectra.