Two mono- and dinuclear Cu (II) complexes derived from 3-ethoxy salicylaldehyde: X-ray structures, spectroscopic, electrochemical, antibacterial activities, Hirshfeld surfaces analyses, and time-dependent density functional theory studies

The quinazoline-type ligand 2-(3-ethoxy-2-hydroxyphenyl)-4-methyl-1,2-dihydroquinazolin 3-oxide (HL1, H is the deprotonatable hydrogen) was synthesized. Two mono- and dinuclear Cu (II) complexes, [Cu(L-2)(2)]center dot 2CH(3)OH (1), and [Cu-4(L-2)(4)(NO3)(2)] (2) (HL2 = 1-(2-{[(E)-(3-ethoxy-2-hydroxybenzylidene]amino}phenyl)ethanone oxime), were obtained via complexation of HL1 with Cu (II) acetate monohydrate or Cu (II) nitrate trihydrate in methanol. HL1 and both complexes were characterized by elemental analyses and spectroscopic methods. The structures of complexes were confirmed by single-crystal X-ray crystallography and the ratio of ligand to metal in 1 was 2:1 whereas 2 was 1:1. In the crystal structures, hexa-coordinated Cu (II) complex 1 was assembled into an infinite 1-D, 2-D network and 3-D supramolecular framework. Complex 2 included four deprotonated (L-2)(-) units, four coordinated Cu (II) and two coordinated nitrate anions, forming an infinite 2-D layer and interesting butterfly-shaped 3-D supramolecular skeleton. Specifically, the Cu1 and Cu4 centers were four-coordinated, while the Cu2 and Cu3 centers were penta-coordinated in 2. Furthermore, electrochemical properties and antibacterial activities of both complexes were also investigated. In addition, the electron paramagnetic resonance (EPR) spectra of 1 and 2 were also studied. The optimal geometries, HOMO-LUMO energies and molecular electrostatic potential diagrams of two complexes were calculated using density functional theory (DFT)/B3LYP, and specific electronic transitions in the UV-vis spectra of 1 and 2 were recorded by time-dependent DFT (TD-DFT) calculations. Additionally, the noncovalent interactions between both complexes were also confirmed by Hirshfeld surfaces.