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Two novel complexes [Zn(L)2·(NO3)2] (1) and [Ni(L)2·2H2O]·2CH3OH·(NO3)2 (2) (L = 2‐(2‐thiazolyl)‐4‐methyl‐1,2‐dihydroquinazoline‐N3‐oxide) were synthesized successfully and characterized by elemental analysis, as well as various spectroscopic techniques. Specifically, the photoluminescence behavior of complex 1 was explored in different solvents. The structural characterization of both complexes has been determined single‐crystal X‐ray diffraction. It revealed that the metals in 1 and 2 are chelated by two L ligands in centro‐symmetrically fashion and the complexes are counterbalanced by nitrate ions which act as coordinating species in 1, while two water molecules complete the Ni coordination sphere in 2. In the crystal structures, the adjacent molecules of complex 1 disclosed a ladder‐like 2‐D network and 3‐D supramolecular self‐assembly. Simultaneously, an infinite 1‐D chain, 2‐D layered skeleton, and even meter‐shaped 3‐D network of 2 was governed by molecular interactions (H–bonds, C–H⋯π). Most strikingly, the research of antibacterial activity proved that two complexes had good activity against two standard bacteria strains. To ascertain deeply the optimum geometric configurations and detect the frontier molecular orbital energy gaps, density functional theory (DFT) calculations were also investigated. Additionally, analyses of Hirshfeld surfaces (HS) and electrostatic potential (ESP) were also performed to quantify the presence of diverse noncovalent interactions. [ABSTRACT FROM AUTHOR]

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(L2)2]·2CH3OH (1), and [Cu4(L2)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 (L2)− 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. [ABSTRACT FROM AUTHOR]