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

Theortho-substituted (E)-1-((2-methoxyphenyl)diazenyl)naphthalen-2-ol and themeta-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 theirpara-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 pi-pi* (ILCT) transition, while the unique major peak afforded by (II) is assigned to MLCT and LLCT transitions.