Synthesis, spectroscopic characterization, crystal structure and theoretical investigation of two azo-palladium (II) complexes derived from substituted (1-phenylazo)-2-naphtol

The ortho -substituted (E)-1-((2-methoxyphenyl)diazenyl)naphthalen-2-ol and the meta -substituted (E)-1-((3-methoxyphenyl)diazenyl)naphthalen-2-ol were, respectively, used in the synthesis of two new complexes, bis[1-(2-methoxyphenylazo)-2-naphthoxy]palladium(II) and bis[1-(3-methoxyphenylazo)-2-naphthoxy]palladium(II), noted (I) and (II), respectively. (I) and (II) were characterized by physicochemical and spectroscopic methods, and their molecular structures were determined by X-ray crystallography. Both complexes display a square-planar geometry, which is reproduced by full geometry optimizations at the DFT/B3LYP level. Calculations were also performed on the free ligands (in their precursor form), as well as their para- substituted isomer (E)-1-((4-methoxyphenyl)diazenyl)naphthalen-2-ol and its hypothetical complex bis[1-(4-methoxyphenylazo)-2-naphthoxy]palladium(II) (compound (III). Calculations were also performed on the free p-phenylazo-2-naphthol ligand (p-MoxyPhNap), in order to understand their bonding and to analyze their electronic structure. TD-DFT calculations were also performed on the three complexes to simulate their absorption spectra from and compare to the experimental UV–Vis data of (I) and (II). The main peaks in the spectrum of (I) are assigned to mixed LMCT/LLCT and π – π * (ILCT) transition, while the unique major peak afforded by (II) is assigned to MLCT and LLCT transitions.