Molecular and Electronic Structure and Electronic Spectra of 4-[(4-Bromophenyl) Diazenyl]-2-Ethoxyaniline Ligand and its Zn(II) Complex

The molecular and electronic structure of 4-[(4-bromophenyl)diazenyl]-2-ethoxyaniline, (L1), as ligand was calculated by Density Functional Theory (DFT). The bond distances as well as bond and torsion angles in the optimized molecular structure was compared with the already reported X-ray structure determined values. Also, tetrahedral geometry for the Zn(II) complex was proposed with Zn―O and Zn―N bond distances are in accord with those reported for similar N2O2 coordinating complexes. For the optimized free ligand, HOMO is calculated to be π orbital and LUMO is π* orbital and the energy gap of LUMO-HOMO is ~3.25 eV. Whereas, for the optimized [Zn(L1)2]+2 complex, HOMO is predicted to be π(bromophenyldiazophenyl) fragment delocalized on one ligand and LUMO is σ*(Ligand―4s Zn). Moreover, time-dependent density functional theory (TDDFT) calculations were applied to preciously predicting and assigning of the UV-Vis absorption spectra of L1 and [Zn(L1)2] in gas phase. The results showed that the electronic spectra of free ligand is mainly due to π→π* and nb(N=N)→σ*(C―H)ethyl+σ*(N―H) electronic transitions. Strong absorption bands predicted at 426 and 415 nm for [Zn(L1)2]+2 due to π→π* electronic transitions from one ligand to the other one. Accordingly, the color of the [Zn(L1)2]2+ complex was predicted to be yellowish-orange.