DFT, characterization and investigation of vibrational spectroscopy of 4-(4-hydroxy)-3-(2-pyrazine-2-carbonyl)hydrazonomethylphenyl-diazen-yl-benzenesulfonamide and its copper(II) complex

• The ligand and its Cu(II) complex were synthesized and characterized.
• Spectroscopic properties of the ligand and its Cu(II) complex were carried out.
• Geometrical optimization of ligand calculated using DFT/B3LYP with 6-31G* and 6-311G** level.
• The calculated vibrational frequencies showed slight deviation from experimental frequencies for the ligand.
• The reactivity descriptors for ligand H2L and its Cu(II) complex were computed and showed increasing dipole moment of ligand.

Azo-Schiff-base complex of Cu(II) has been synthesized and characterized by elemental, spectral and thermal studies. The conductance data indicate the non-electrolytic nature of the complex. The IR spectra of the prepared complex was suggested that the azo-Schiff-base ligand [4-(4-hydroxy)-3-(2-pyrazine-2-carbonyl)hydrazonomethylphenyl-diazen-yl-benzenesulfonamide] (H2L) behaves as a tri-dentate ligand through the carbonyl oxygen atom, azomethine nitrogen atom and phenolic oxygen atom (ONO). The surface morphology (SEM) of the ligand and its copper(II) complex was studied using SEM analysis. X-ray powder diffraction (XRD) helps to determine the cell parameters of the complex. Transmission electron microscopy (TEM) indicated spherical particles of ∼200 nm diameter. The physico-chemical studies revealed octahedral geometry around copper ion. The EPR spectra of copper complex in DMSO at 300 and 77 K were recorded and their salient feature was reported. The redox behavior of the ligand and its copper(II) complex were studied using cyclic voltammetry. Thermal properties and decomposition kinetics of copper(II) complex was investigated. The interpretation mathematical analysis and evaluation of kinetic parameters (E, A, ΔH, ΔS and ΔG) of all thermal decomposition stages have been evaluated using Coats–Redfern (CR), Horowitz–Metzger (HM) and Piloyan–Novikova (PN) equations. Moreover, the density functional theory studies are discussed for ligand, using DFT/B3LYP with 6-31G* and 6-311G* level of theory, the absorption spectra has been computed by using time dependent at TD-DFT/B3LYP with 6-31G* and 6-311G* level of theory. The HOMO–LUMO energy gap of studied systems has been discussed.

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