A combined first principles TDDFT and experimental study on the UV-Vis spectra properties of M(p-nitrophenyl azo resorcinol)$_{3}$ complexes (M: Fe, Cr)

Abstract

UV-Vis absorption data of p-nitrophenyl azo resorcinol (Magneson I) and its 2 Fe(III) and Cr(III) complexes were investigated both experimentally and theoretically. The geometries were optimized at BP86/TZVP level. The most stable spin states were computed as doublet and quartet for Fe(magneson)_3 and Cr(magneson)_3 complexes, respectively. Time-dependent density functional theory (TDDFT) was employed to explore the absorption spectra properties, whereas the solvent effects were taken into account using the polarizable continuum model (PCM). The M06, B3LYP, and PBE0 hybrid functionals together with TZVP/LANL2TZ basis sets were used for comparing the results with experimental data. The theoretical analysis of electronic structure and molecular orbitals demonstrated that the low-lying absorption bands in the UV-Vis spectra are mainly \pi \to d ligand-to-metal charge transfer (LMCT) transition and \pi \to \pi ligand-to-ligand charge transfer (LLCT) transition for Fe(magneson)_3, and, in addition to that of LMCT and LLCT, d \to \pi metal-to-ligand charge transfer (MLCT) transition for Cr(magneson)_3 complexes. The good agreement between the experimental and TDDFT calculation, especially M06 and B3LYP absorption spectra of the metal Magneson I complexes, allowed us to provide a detailed estimation of the main spectral features of ferric and chromic complexes.