Mono- and binuclear copper(II) complexes with different structural motifs and geometries: Synthesis, spectral characterization, DFT calculations and superoxide dismutase enzymatic activity

Several new copper(II) mono- and binuclear complexes, [Cu(HL)(ClO4)(H2O)]CH3OH (1), [Cu(HL)(DMF)] (ClO4) CH3OH (2), [Cu-2(HL)(2)(pyrazine)](ClO4)(2) (3) and [Cu-2(HL)(2)(4,4-bipy)(ClO4)(2)]2H(2)O (HL = 4-bromo-2-(pyridine-2-ylhydrazonomethyl)-phenol, 4,4-bipy = 4,4-bipyridyl) have been synthesized and characterized by elemental analysis, FTIR, UV-vis and electron paramagnetic resonance (Epr) spectroscopy. Molecular structures of all complexes have been obtained using single crystal X-ray analysis. The geometry of copper(II) in 1 is distorted square pyramidal and distorted square planar in 2. In binuclear complexes each copper(II) centre has distorted square planar and distorted square pyramidal geometry in 3 and 4, respectively. The complexes 1-4 possess the self-assembled supramolecular structures via different molecular interactions (hydrogen bondings, CH center dot center dot center dot pi and pi center dot center dot center dot pi stacking interactions). The possible intermolecular interactions were explored using 3D Hirshfeld surface and related 2D fingerprint plots, spectroscopic properties were studied using UV-visible and electron paramagnetic resonance techniques. Optimized geometry, frontier molecular orbital (FMO) and natural bond order (NBO) analysis were performed using density functional theory (DFT) calculations. To predict the chemical reactivity of complexes some global reactivity descriptors (chemical potential electronegativity x, hardness eta and electrophilicity index omega) have been evaluated using DFT. The low temperature magnetic susceptibility measurements of binuclear complexes have been obtained predicts the magnetic exchange coupling value (J) by variable temperature measurements. The magnetic exchange coupling value (J) obtained are -8.1 and -2.4 cm(-1) for 3 and 4, respectively. The superoxide dismutases (SOD) of all complexes were measured using NBT assay method. The complexes show moderate superoxide dismutase (SOD) mimetic activity.