Syntheses, spectroscopy, cyclic voltammetry, thermal analyses, EPR, and DFT/TDDFT on bis[N-2-(R-pyridyl)salicylaldiminato-κ2NˆO]copper(II) (R = H, 4/6-CH3)

Abstract

Bis[N-2-(R-pyridyl)salicylaldiminato-κ2NˆO]copper(II) (R = H: 1, 4/6-CH3: 2/3) are synthesized and characterized by UV–Vis., IR, mass, cyclic voltammetry, magnetic moment, DSC, EPR and DFT/TDDFT, respectively. Mass spectra show parent ion peaks at m/z 458 (1) and 486 (2 or 3). Electronic spectra feature different bands for intra-ligand (<350 nm), metal-ligand (350–540 nm) and metal-metal (540–940 nm) transitions, respectively. Spectra in different solvents show a blue shift of absorption maxima with increasing polarity, dielectric constants and donor/acceptor number of solvent, respectively. DSC analyses show an irreversible phase transformation from crystalline to isotropic liquid phase. CV studies demonstrate a quasi-reversible two electrons charge transfer processes for [Cu(L)2]0/[Cu(L)2]− and [Cu(L)2]–/[Cu(L)2]2− (L = deprotonated Schiff base ligand) couples, respectively in acetonitrile. EPR spectrum in chloroform shows an isotropic pattern with four lines due to nuclear hyperfine splitting from copper(II) with spin 3/2, and giso value of 2.1244, indicating considerable covalent character in M–L bonds. Magnetic moment values (μ = 1.49–1.61 μB) in methanol indicate the formation of copper(II)-NˆO-chelate complexes with one unpaired electron. The optimized structures and excitation properties studied by DFT/TDDFT are comparable to the experimental results.