Theoretical study of relationships between structural, optical, energetic, and magnetic properties and reactivity parameters of benzidine and its oxidized forms.

Structural, topological, optical, energetic, and magnetic properties and reactivity parameters of benzidine, its radical cation, and its dication as well as molecular complexes of the benzidine dication with the F(-), Cl(-), Br(-), I(-), NO3(-), HSO4(-), and H2PO4(-) anions were calculated at the B3LYP/6-311++G(2d,2p) level of theory in the CH2Cl2 medium. The CAM-B3LYP functional (as the most reliable one) and the 6-311++G(3df,3pd) basis set were used for the UV-vis absorption spectra prediction. The obtained spectral results are in a good agreement with available experimental data. A number of the calculated global and local molecular properties, including several recently developed ones, (in general, more than 20 parameters), namely, λmax, the bond lengths and orders (l and LA,B), adiabatic ionization energy (IEad), global electrophilicity index (ω), condensed electrophilic Fukui functions (f(+)) and dual descriptor (ΔfA), van der Waals molecular volume, nuclear independent chemical shifts (NICS) and QTAIM topological parameters were estimated in the critical points of the C(1)-C(1'), C(2)-C(3), and C(4)-N bonds as well as at the ring critical point. These quantities were found to be in a strong linear dependence (R(2) > 0.99 in most cases) with the number of detached electrons (Nel) from the benzidine molecule up to formation of the dication (Nel = 2). On one hand, a position of the long-wave absorption band (λCT) corresponding to the anion-to-cation charge transfer in the neutral complexes of the benzidine dication with anions, correlates with the Mulliken electronegativity of the anion (R(2) = 0.8646) and its adiabatic ionization energy (R(2) = 0.8054). On the other hand, the correlations with the anion charge in the complexes and the anion isotropic polarizability are rather poor (R(2) = 0.6392 and 0.3470, respectively). On the ground of the obtained strong relationships, one may recommend the calculated molecular properties as potentially preferable descriptors for the benzidine-based compounds in terms of the QSAR methodology.