High spin ground state copper(II) and nickel(II) complexes possessing the 3,5-di-tert-butyl-1,2-semiquinonate radical anion

Cu(II) complexes with a salicylaldehyde derivative and α-diimines as co-ligands: synthesis, characterization, biological activity. Experimental and theoretical approach

Copper(II) complexes with an α-diimine show a wide variety of biological activities, such as antibacterial, antifungal, antioxidant and anticancer. In this work, we synthesized and structurally characterized two novel Cu(II) complexes with methyl 3-formyl-4-hydroxybenzoate (HL) and α-diimines: 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen). Crystal structure analysis shows that the formulas of the compounds are [Cu(bipy)(L)(BF4)] (1) and [Cu(phen)(L)(H2O)](BF4)·H2O (2), with BF4- as a ligand in complex 1, which is rarely coordinated to metals. Both complexes have a square pyramidal geometry, while DFT calculations showed that the most stable structures of complexes 1 and 2 in a water/DMSO mixture are square-planar derivatives [Cu(bipy)(L)]+ and [Cu(phen)(L)]+. The antibacterial activity of compounds was evaluated in vitro on four Gram-negative and four Gram-positive bacterial strains. Complex 2 showed greater antibacterial activity towards all bacterial strains comparable to the control compound Amikacin. Complex 2 exerted a strong cytotoxic effect against the tested cancer cell lines (IC50 values ranging from 0.32 to 0.44 μM). Both complexes caused apoptotic cell death in HeLa cells and a noticeable in vitro antiangiogenic effect. In the concentration range of 5 to 100 μM, the complexes showed the absence of a genotoxic effect and displayed a protective effect against oxidative DNA damage induced by H2O2 in human peripheral blood cells. The interaction between the compounds and calf-thymus DNA was evaluated by diverse techniques suggesting a tight binding, which was also confirmed by molecular docking. In addition, it was found that the complexes bind tightly and reversibly to bovine and human serum albumin.

Understanding the Exchange Interaction between Paramagnetic Metal Ions and Radical Ligands: DFT and Ab Initio Study on Semiquinonato Cu(II) Complexes

The exchange coupling, represented by the J parameter, is of tremendous importance in understanding the reactivity and magnetic behavior of open-shell molecular systems. In the past, it was the subject of theoretical investigations, but these studies are mostly limited to the interaction between metallic centers. The exchange coupling between paramagnetic metal ions and radical ligands has hitherto received scant attention in theoretical studies, and thus the understanding of the factors governing this interaction is lacking. In this paper, we use DFT, CASSCF, CASSCF/NEVPT2, and DDCI3 methods to provide insight into exchange interaction in semiquinonato copper(II) complexes. Our primary objective is to identify structural features that affect this magnetic interaction. We demonstrate that the magnetic character of Cu(II)-semiquinone complexes are mainly determined by the relative position of the semiquinone ligand to the Cu(II) ion. The results can support the experimental interpretation of magnetic data for similar systems and can be used for the in-silico design of magnetic complexes with radical ligands.

Synthesis and Characterization of Catecholato Copper(II) Complexes with Sterically Hindered Neutral and Anionic N3 Type Ligands: Tris(3,5-diisopropyl-1-pyrazolyl)methane and Hydrotris(3,5-diisopropyl-1-pyrazolyl)borate

Three catecholato copper(II) complexes, [Cu(catCl4)(L1′)], [Cu(catBr4)(L1′)], and [Cu(catCl4)(L1H)], supported by sterically hindered neutral and anionic N3 type ligands: tris(3,5-diisopropyl-1-pyrazolyl)methane (referred to as L1′) and hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (referred to as L1−), are synthesized and characterized in detail. Their X-ray structures reveal that both [Cu(catCl4)(L1′)] and [Cu(catBr4)(L1′)] complexes have a five-coordinate square-pyramidal geometry and [Cu(catCl4)(L1H)] complex has a four-coordinate square-planar geometry. The L1H is unusual protonated ligand that controls its overall charge. For the three catecholato copper(II) complexes, the oxidation state of copper is divalent, and catechol exists in catecholate as two minus anion. This difference in coordination geometry affects their d-d and CT transitions energy and ESR parameters.

Novel dioxolene nickel complexes with sterically hindered diazabutadienes. Coupling of aza-ligands coordinated to nickel

Coupling of nickel complexes containing N,N′-disubstituted-2,3-dimethyl-1,4-diazabutadiene-1,3 occurs through the methyl group of the latter in nonpolar media in the presence of free o-quinone.