Vibrational spectroscopic investigation and DFT studies on 2,2′,4,4′-tetrabromodiphenyl ether

In the present work, the infrared (IR) and Raman spectra of 2,2′,4,4′-tetrabromodiphenyl ether have been measured in the ranges of 400–4000 cm−1 and 100–4000 cm−1. The geometry optimized by the density functional theory Becke-3-Lee-Yang-Parr (B3LYP) method with the 6-31G(d) basis set was in good agreement with the experimental data of analogues. The results have shown that the dihedral angle of biphenyl ether significantly increases with the addition of bromine substitution. The vibrational frequencies were evaluated by the B3LYP method in conjunction with basis sets of 6-31G(d), 6-31G(2df,p), 6-311+G(d,p), 6-311G+(2df,p), and 6-311++G(d,p), separately. The scaled frequencies resulted in excellent agreement with the observed spectral patterns. The correlation analysis and statistical comparisons indicated that the basis sets larger than 6-31G(d) resulted in no significant improvement in the accuracy of the vibration frequencies. The detailed assignments were performed according to the calculated results for B3LYP/6-31G(d) and then compared with those from a previous study on 4,4′-dibromodiphenyl ether. The absence of coupling of C–O stretching and adjacent C–H in-plane deformation indicated a strong steric effect owing to the ortho bromine atoms in the title compound. Moreover, the quantum theory of atoms in molecules (QTAIM) and the Moller–Plesset second-order perturbation (MP2) method are applied to exclude the possible formation of intramolecular non-covalent interactions such as Br⋯Br and C–H⋯Br.