Ab initio and density functional study of the geometrical, electronic and vibrational properties of 3,4′-bi-1,2,4-triazole

The conventional ab initio method at the closed restricted Hartree-Fock level (RHF) and the density functional theory (DFT) approach at the B3-LYP level, using the 6-31+G* basis set, are applied to predict the molecular structure and the energetic and the vibrational properties (harmonic wave numbers, force fields and potential energy distributions) of the 3,4′-bi-1,2,4-triazole and of two deuterated derivatives (ND and ND(CD)3). The theoretical results are compared to the Raman and infrared vibrational data. Using both methods, there is a very good agreement between theory and experiment concerning not only the wave numbers but also the isotopic shifts. This accordance allows us to validate the calculated structure of bTA. This molecule is characterized by an aromatic structure in which two triazolic rings are linked by a CN bond, intermediary between a single and double bond, in a planar conformation. From a methodological point of view, the B3-LYP method predicts more accurate structure and harmonic vibrational wave numbers than the RHF method.