Supramolecular compounds of azo dyes derived from 1-phenylazo-2-naphthol and their nickel and copper complexes

In this study, experimental techniques including Raman, infrared and X-ray crystal diffraction, as well as quantum chemistry calculations, are used to investigate two new azo dyes supramolecular complexes: 1-phenylazo-2-naphthol (Sudan I) with nickel(II) ion and 1-(2,4-xylylazo)-2-naphthol (Sudan II) with copper(II) ion. The crystallographic structures have been solved for bis-1-(pheny-l-azo)-2-naphtholatenickel(II) and bis-1-(2,4-xylylazo)-2-naphtholatecopper(II) complexes, revealing the presence of supramolecular interactions, such as the centroid–centroid π-stacking interactions and CH…π hydrogen interactions. These weak intermolecular interactions appear to play an important role on the crystal structure stability for both compounds. Density functional theory calculations at B3LYP/6-311++G(d,p) level were performed in order to help understanding such molecular interactions and to assign the vibrational spectra. The experimental and theoretical data have allowed the analysis of the packing forces, revealing charge accumulation at key molecular regions.