Dinuclear Copper Complexes Research Articles

A Multichromotropic Dinuclear Copper(II) Complex: Unveiling its Structural and Spectroscopic Properties

A Multichromotropic Dinuclear Copper(II) Complex: Unveiling its Structural and Spectroscopic Properties

Dinuclear Copper(II) Complex with Intramolecular O–H⋅⋅⋅O Hydrogen Bonding: Magneto‐Structural Correlation for Acylhydrazone‐Based Phenoxido Bridged Copper(II) Complexes

The μ‐phenoxido‐bridged dinuclear copper(II) complex, [Cu2(L1)2(dmso)(MeOH)] (1), has been synthesized using N′‐(4‐(diethylamino)‐2‐hydroxybenzylidene)‐1‐naphthohydrazide (H2L1) as ligand. The structural analysis of 1 reveals that the coordination geometry at the copper ions is best described as a square pyramidal with a Cu···Cu distance in the dinuclear complex of 303 pm which is supported by hydrogen bonding between the two apical oxygen donor ligands (O···O 277 pm). Magnetic studies indicate that 1 exhibits a strong antiferromagnetic interaction between the two copper(II) ions with a coupling constant of J = −450 cm−1. The magnetic exchange is transmitted through the central [Cu2(OR)2]2+ core, a fragment for which different magneto‐structural correlations have been reported depending on the substituent at the bridging oxygen atom. However, the properties of complex 1 cannot be explained by any of the established correlations. Nevertheless, complex 1, together with the series of compounds based on an acylhydrazone ligand framework reported so far, shows a magneto‐structural correlation as a function of the Cu−O−Cu bridging angle that significantly differs from all previously reported.

Glucoconjugated Dinuclear Copper(II) Complex: An Efficient Catalyst for Stereoselective Synthesis of Trisubstituted Propargylamines via Solvent-free A3 Coupling Reaction.

Development of catalytic systems using nontoxic natural precursors is the need of the era, and along this line, we have synthesized a new D-glucose derived ligand (4,6-O-ethylidene-N-(2-hydroxy-4-(octyloxy)benzylidene)-β-D-glucopyranosylamine) and its dinuclear copper(II) complex. The molecular structure of the complex has been established by single-crystal X-ray diffraction studies and detailed noncovalent intermolecular interactions present in it have been explored by Hirshfeld surface analysis. Further, the complex has been used as a catalyst in the enantioselective (87-99 % ee) synthesis of propargylamines in good to excellent yield (82-95 %) via aldehyde-amines-alkynes (A3) coupling reaction under solvent-free condition. The formation of aminal intermediate during the reaction has been confirmed by 1H-NMR and single-crystal X-ray diffraction studies. The catalytic system is reusable without any appreciable loss in the enantioselectivity or product yield.

Syntheses, characterization and antibacterial activity of mononuclear and dinuclear copper(II) complexes containing a hydrazone ligand

An aroylhydrazone compound (HL) was prepared and explored as a ligand (HL = N’-(2-hydroxy-4-methoxybenzylidene)-3-hydroxy-4-methoxybenzohydrazide). Reaction of the aroylhydrazone ligand with copper bromide and copper chloride afforded two new copper(II) complexes, [Cu2Br2L2] (1) and [CuL(DMF)]Cl (2), respectively. The aroylhydrazone ligand and copper complexes were characterized by CHN elemental analyses and infrared spectroscopy. Structures were further confirmed by single crystal X-ray diffraction experiments. The aroylhydrazone compound coordinates to Cu atoms through its phenolate oxygen, imino nitrogen and carbonyl oxygen. The Cu atom in 1 adopts a square pyramidal coordination, with three donor atoms of one L and one phenolate oxygen of a second L in the basal plane, and with one Br ligand at the apical position. The Cu atom in 2 is square pyramidal, with three donor atoms of one L and one oxygen of a DMF ligand in the basal plane, and with one Cl ligand at the apical position. Crystal structures of the aroylhydrazone and the copper complexes are stabilized by hydrogen bonds. The complexes possess antibacterial activities against B. subtilis, S. aureus and E. coli.

Dithiodipropionate and Fumarate Ni, Cu, and Zn Mixed Ligand Complexes

Three nickel, copper, and zinc complexes with dicarboxylic acids (3,3′-dithiodipropionic acid (H2dtdp) and fumaric acid (H2fu)) and N-donor ligands (1,10-phenanthroline (phen), N′–methyldipropylenetriamine (mdpta), and N,N,N′,N″,N″-pentamethyldiethylenetriamine (pmdien)) were synthesized. These complexes were characterized using elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. Interestingly, [Ni(dtdp)(phen)(H2O)3]∙0.5H2O (1) is a mononuclear complex, where the dtdp dianion employs only one carboxylate group for coordination to the central nickel atom. [(ClO4)(mdpta)Cu(μ-dtdp)Cu(mdpta)(H2O)](ClO4) (2) is a dinuclear copper complex with a dtdp bridge and different coordination on the copper center. [{Zn(pmdien)(H2O)}2(μ-fu)](ClO4)2 (3) is a symmetric dimer with a bridging fumarate ligand. These coordination compounds were tested for their antibacterial activities on Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis bacteria strains. All the complexes show moderate activities on the mentioned strains.

Bio-inspired copper complexes with Cu2S cores: (solvent) effects on oxygen reduction reactions.

The need for effective alternative energy sources and "green" industrial processes is a more crucial societal topic than ever. In this context, mastering oxygen reduction reactions (ORRs) is a key step to develop fuel cells or to propose alternatives to energy-intensive setups such as the anthraquinone process for hydrogen peroxide production. Achieving this goal using bio-inspired metal complexes based on abundant and non-toxic elements could provide an environmentally friendly option. Given the prevalence of Cu-containing active sites capable of reductive activation of dioxygen in nature, the development of Cu-based catalysts for the ORR thus appears to be a relevant approach. We herein report the preparation, full characterization and (TD)DFT investigation of a new dinuclear mixed-valent copper complex 6 exhibiting a Cu2S core and a bridging triflate anion. Its ORR activity was compared with that of its parent catalyst 1. Two types of solvents were used, acetonitrile and acetone, and various catalyst/Me8Fc (electron source) ratios were tested. Our results highlight a counterintuitive solvent effect for 1 and a drastic drop in the activity for 6 in coordinating acetonitrile together with the modification of its chemical structure.

Development of pivalic acid conjugated Nafion modified glassy carbon electrode for sensitive detection of Cu(II) by electrochemical approach

In this work, pivalic acid (pivH) molecule is employed for an electrochemical sensing of copper cations in an aqueous medium. For sensitive as well as selective potential sensor application, pivH was fabricated onto a glassy carbon electrode (GCE) facilitated by adhesive conducting binder, nafion, so as make it selective and effective electrochemical probe (pivH/Nafion/GCE) towards specific heavy metal cations. This newly fabricated pivH/Nafion/GCE reveals enhance electrochemical activity toward copper ions in the presence of other interfering heavy metal cations in phosphate buffer solution (PBS) of pH=7. The calibration plot was linear (r2 = 0.9879) across broad linear dynamic range (LDR) spanning Cu2+ concentration from 0.1 nM to 0.01 M. The sensitivity and detection limit was found to be 0.0212 × 10−2 µAµM−1cm−2 and 0.014 nM, respectively. So, this newly fabricated GCE as selective electrochemical probe offers a sensitive as well as selective detection of Cu2+ cations in real environmental samples using a novel electrochemical, current–potential (I-V), approach, for the first time. Further, we explored pivalic acid for the preparation of new di-nuclear copper complex, [Cu2(piv)4(pivH)2] (where piv = pivalate; pivH=pivalic acid) and characterized by Fourier transform infrared spectroscopy (FTIR) spectroscopy, elemental analysis and single crystal X-ray diffractometry. Density functional theory (DFT) calculations were carried out to confirm the interactions and these calculations well-support to experimental data. In case of deprotonated form of pivH, Molecular Electrostatic Potential (MEP) analysis exhibits electrostatic potential equals to −148.4 kcal/mol which suggest about the strong interaction of –COOH with copper centers. Similarly, interaction energies, the quantum theory of atoms in molecules (QTAIM) study and Natural Bond Orbital (NBO) analysis also favor to experimental work. Thus, this novel study demonstrates an excellent approach for highly selective and sensitive detection of Cu2+ cations in short response time with low detection limit and good reproducibility by using I-V method based on newly designed pivH/Nafion/GCE as selective Cu2+ cationic electrochemical sensor. The experimental data was compactable with theoretical calculations.

Structural Investigation of Schiff Base Ligand and Dinuclear Copper Complex: Synthesis, Crystal Structure, Computational, and Latent Fingerprint Analysis.

The structural studies of the fluorinated Schiff base ligand and its copper complex were synthesized and characterized by Fourier transform infrared, UV-visible, and photoluminescence spectroscopy. Single-crystal X-ray diffraction analysis unveils a dinuclear copper complex arising from double bridging acetate anions to copper ions that are chelated by the tridentate Schiff base ligand Cu(LS). The trigonality index τ5 of 0.080 indicates a distorted square pyramidal coordination geometry for the metal. The SL ligand and complex exhibit intra- and intermolecular interactions, leading to unique supramolecular architectures. The structural changes between the free halogenated Schiff base ligand and upon coordination with the metal were extensively studied by experimental and theoretical approaches. The intra- and intermolecular interactions have been analyzed by Hirshfeld surface and quantum theory of atoms in molecules analysis, and the enrichment ratio highlights the most favored interactions in the formation of molecular packing. The chemical and physical properties, such as the HOMO - LUMO energy gap, chemical reactivity, and electron density topology, are studied using density functional theory studies. In addition, the Schiff base ligand compound is used to study the latent fingerprint analysis.

Synthesis of Asymmetric Variants in a Dinucleating Ligand Family and Application for Dinuclear Copper(II) Complexes

AbstractWe developed a dinucleating ligand system with two identical tetradentate coordination compartments and varying terminal donors. Here, we report the synthesis of two differently asymmetric dinucleating ligands: the ligand selma (=4,7,10‐trimethyl‐1,1,10‐tris(2‐pyridylmethyl)‐1,4,7,10‐tetraazadecane) with one N3‐ and one N4‐ and the ligand susan (=4,7‐dimethyl‐1,1‐bis(6‐methylpyridine‐2‐yl‐methyl)‐10,10‐bis(2‐pyridylmethyl)‐1,4,7,10‐tetraazadecane) with two different N4‐coordination compartments. The initial synthesis of the ligand selma based on extending dipicolylamine with 2‐(methylamino)ethyl units in repeated reductive aminations. Synthesis of 1‐trifluoroacetyl‐4,7‐dimethyl‐1,4,7,10‐tetraazadecane allowed the synthesis of both ligands selma and susan . To study the influence of the terminal donors, the CuII chloride complexes of selma and susan and the two symmetric susan and susan6−Me were synthesized. The introduction of the 6‐methyl substituents on the pyridines increases the bond lengths, reduces the electron donation, and shifts the reduction potentials anodically. The large 6‐methyl substituents enforce a meridional coordination of the dipicolylamine subunits, while it is mainly facial without the 6‐methyl substituents. Analysis of the solid‐state structures and the d‐d transitions in solution demonstrate a flat potential energy surface for the 5‐coordinate polyhedra. Analysis of d‐d transitions and reduction potentials indicate that the properties of the CuIICuII complexes are additive for but cooperative for selma reflecting the difference of these asymmetric dinucleating ligands.

Theoretical and electrochemical analysis of halogenated salmphen-type dinuclear copper(II) complex: The influence of halogenated ligands on bandgap

The predictable control of energy levels in coordination polymer is an essential issue in molecular science. To explore a simple and feasible strategy for tuning the energy levels of Schiff base materials, the present work synthesized a novel halogen-substituted cofacial Schiff base compound, CuII2(2-Cl-Salmphen)2 (Cu-2-Cl-Salmphen), and the non-halogenated analogue CuII2(H-Salmphen)2 (Cu-H-Salmphen) was introduced for comparison. Experimental results show that the introduction of halogen atoms can effectively increase the absorbance and decrease the impedance of the compound. Further theoretical analyses revealed that the substitutional halogen atoms can not only enlarge the conjugation area but also change the electron density and the molecular orbital energy levels, thus enabling modulation of the bandgap values of the compounds. Besides, NCI studies have demonstrated that the substitution of halogens can form additional intermolecular interaction pathways, adjusting the interactions between adjacent molecules.

A Dinuclear Copper(II) Complex Electrochemically Obtained via the Endogenous Hydroxylation of a Carbamate Schiff Base Ligand: Synthesis, Structure and Catalase Activity.

In the present work, we report a neutral dinuclear copper(II) complex, [Cu2(L1)(OH)], derived from a new [N,O] donor Schiff base ligand L1 that was formed after the endogenous hydroxylation of an initial carbamate Schiff base H2L coordinated with copper ions in an electrochemical cell. The copper(II) complex has been fully characterized using different techniques, including X-ray diffraction. Direct current (DC) magnetic susceptibility measurements were also performed at variable temperatures, showing evidence of antiferromagnetic behavior. Its catalase-like activity was also tested, demonstrating that this activity is affected by temperature.

Modelling the Binding of Cytotoxic Dinuclear Copper Complexes to two Neighboring Phosphate Esters of DNA Using Glutarate: A Tetranuclear Metallo‐Macrocycle vs a Dinuclear Model

AbstractA family of dinuclear complexes was rationally designed to bind to two neighboring phosphate diesters of DNA by molecular recognition. Although these complexes bind strongly and irreversibly to DNA and induce apoptosis in cancer cells, a direct proof of the intended binding mode is missing. To mimic two neighboring phosphate diesters of DNA, we use here the dicarboxylate glutarate as a difunctional ligand. Starting from the acetate‐bound CuII2 complex, protonation results in the de‐coordination of acetate and allows the synthesis of the glutarate‐bound complex. Instead of bridging two CuII ions of one dinuclear complex, two glutarates bridge two dinuclear complexes resulting in a tetranuclear metallo‐macrocycle. The molecular structures of two different salts differ in the square‐pyramidal coordination to the CuII ions. The carboxylate stretching modes, the d‐d and the CT transtitions are not sensitive enough to resolve these differences. The exchange coupling is weakly antiferromagnetic between the CuII ions in the dinuclear subunits and negligible between the subunits via the glutarates. The consequences for suited ligands to model the binding to two neighboring phosphate diesters in the DNA backbone is discussed.

Dinuclear copper(II) complexes with a bridging bis(chalcone) ligand reveal considerable in vitro cytotoxicity on human cancer cells and enhanced selectivity

A bis(chalcone) molecule (H2L) was synthesized via Aldol's condensation from terephthalaldehyde and 2′-hydroxyacetophenone and it was used as bridging ligand for the preparation of five dinuclear copper(II) complexes of the composition [Cu(NN)(μ–L)Cu(NN)](NO3)2⋅nH2O (n = 0–2) (1–5), where NN stands for a bidentate N-donor ligand such as phen (1,10-phenanthroline, 1), bpy (2,2′-bipyridine, 2), mebpy (5,5′-dimethyl-2,2′-dipyridine, 3), bphen (bathophenanthroline, 4) and nphen (5-nitro-1,10-phenanthroline, 5). The compounds were characterized by different suitable techniques to confirm their purity, composition, and structure. Moreover, the products were evaluated for their in vitro cytotoxicity on a panel of human cancer cell lines: ovarian (A2780), ovarian resistant to cisplatin (A2780R), prostate (PC3), osteosarcoma (HOS), breast (MCF7) and lung (A549), and normal fibroblasts (MRC-5), showing significant cytotoxicity in most cases, with IC50 ≈ 0.35–7.8 μM. Additionally, the time-dependent cytotoxicity and cellular uptake of copper, together with flow cytometric studies concerning cell-cycle arrest, induction of cell death and autophagy and induction of intracellular ROS/superoxide production in A2780 cells, were also performed. The results of biological testing on A2780 cells pointed out a possible mechanism of action characterized by the G2/M cell cycle arrest and induction of apoptosis by triggering the intrinsic signalling pathway associated with the damage of mitochondrial structure and depletion of mitochondrial membrane potential. SynopsisDinuclear Cu(II) complexes bearing a bridging bis(chalcone) ligand revealed high in vitro cytotoxicity, initiated A2780 cell arrest at G2/M phase and efficiently triggered intrinsic pathway of apoptosis.

Mechanochromic photoluminescence in a dinuclear alkynyl copper(i) complex with an extremely short Cu(i)⋯Cu(i) separation

Mechanochromic phosphorescence of a rare copper(i) dinuclear complex with an extremely short Cu(i)⋯Cu(i) separation.

Synthesis, structure and biological properties of a series of dicopper(bis-thiosemicarbazone) complexes

A series of dinuclear copper(ii) complexes obtained with various phenol-bis-thiosemicarbazone ligands are investigated revealing a large diversity in structures and biological properties comparable to those of drugs of reference.

Chemical fixation of atmospheric CO2 in tricopper(II)-carbonato complexes with tetradentate N-donor ligands: reactive intermediates, probable mechanisms, and catalytic and magneto-structural studies.

In the present era, the fixation of atmospheric CO2 is of significant importance and plays a crucial role in maintaining the balance of carbon and energy flow within ecosystems. Generally, CO2 fixation is carried out by autotrophic organisms; however, the scientific community has paid substantial attention to execute this process in laboratory. In this report, we synthesized two carbonato-bridged trinuclear copper(II) complexes, [Cu3(L1)3(μ3-CO3)](ClO4)3 (1) and [Cu3(L2)3(μ3-CO3)](ClO4)3 (2) via atmospheric fixation of CO2 starting with Cu(ClO4)2·6H2O and easily accessible pyridine/pyrazine-based N4 donor Schiff base ligands L1 and L2, respectively. Under very similar reaction conditions, the ligand framework embedded with the phenolate moiety (HL3) fails to do so because of the reduction of the Lewis acidity of the metal center, inhibiting the formation of a reactive hydroxide bound copper(II) species, which is required for the fixation of atmospheric CO2. X-ray crystal structures display that carbonate-oxygen atoms bridge three copper(II) centers in μ3syn-anti disposition in 1 and 2, whereas [Cu(HL3)(ClO4)] (3) is a mononuclear complex. Interestingly, we also isolated an important intermediate of atmospheric CO2 fixation and structurally characterized it as an anti-anti μ2 carbonato-bridged dinuclear copper(II) complex, [Cu2(L2)2(μ2-CO3)](ClO4)2·MeOH (2-I), providing an in-depth understanding of CO2 fixation in these systems. Variable temperature magnetic susceptibility measurement suggests ferromagnetic interactions between the metal centers in both 1 and 2, and the results have been further supported by DFT calculations. The catalytic efficiency of our synthesized complexes 1-3 was checked by means of catechol oxidase and phenoxazinone synthase-like activities. While complexes 1 and 2 showed oxidase-like activity for aerobic oxidation of o-aminophenol and 3,5-di-tert-butylcatechol, complex 3 was found to be feebly active. ESI mass spectrometry revealed that the oxidation reaction proceeds through the formation of complex-substrate intermediations and was further substantiated by DFT calculations. Moreover, active catalysts 1 and 2 were effectively utilized for the base-free oxidation of benzylic alcohols in the presence of air as a green and sustainable oxidant and catalytic amount of TEMPO in acetonitrile. Various substituted benzylic alcohols smoothly converted to their corresponding aldehydes under very mild conditions and ambient temperature. The present catalytic protocol showcases its environmental sustainability by producing minimal waste.

Enhancing oxygen reduction activity of dinuclear copper complexes loaded on an N-doped carbon support via a low-temperature pyrolysis strategy.

Bioinspired by the active sites of multicopper oxidases (MCOs), bi/multinuclear copper complexes have attracted great attention in promoting catalytic activity for the oxygen reduction reaction (ORR). Herein, we report the preparation of a Cu-N-C electrocatalyst Cu-BPOZ@CNB-400 for efficient ORR, which was obtained by low temperature pyrolysis of a dinuclear 2,5-bis(2-pyridyl)-1,3,4-oxadiazole (BPOZ) copper complex loaded on a N-doped carbon support at 400 °C. Cu-BPOZ@CNB-400 exhibited a half-wave potential (E1/2) of 0.86 V vs. RHE for the ORR in 0.1 M KOH solution, which was significantly higher than that of the Cu-BPOZ@CNB-800 (E1/2 = 0.83 V) catalyst treated under high temperature (at 800 °C) and the control catalyst Cu-Phen@CNB-400 (E1/2 = 0.82 V) derived from low-temperature-treatment (at 400 °C) of a mononuclear phenanthroline-coordinated-Cu complex loaded on a N-doped carbon support. When Cu-BPOZ@CNB-400 was applied as the cathode catalyst in zinc-air batteries a maximum power density (Pmax) of 127 mW cm-2 could be achieved, demonstrating comparable catalyst performance to the commercial 20 wt% Pt/C (Pmax = 122 mW cm-2) and the control Cu-Phen@CNB-400 catalyst (Pmax = 105 mW cm-2) under similar experimental conditions. Low-temperature pyrolysis of dinuclear copper complexes on a carbon support improved the charge transfer efficiency, inhibited metal aggregation, and could produce highly dispersed Cu-N-C catalysts with dinuclear copper sites for promoting the 4e--reduction selectivity of the ORR. It thus provides a cost-effective approach for the controllable fabrication of efficient ORR catalysts to be applied for energy conversion devices.

Structural, spectroscopic, theoretical calculation and Hirshfeld surface analyses of 3-D supramolecular dinuclear zinc(II) and copper(II) complexes

Two three-dimensional dinuclear zinc(II) and copper(II) complexes, [Zn2(L2)2(CH3COO)2] (1) and [Cu2(L2)2(NO3)2] (2) (HL2 = 1-(2-{[(E)-2-hydroxy-benzyli-dene]amino}phenyl)ethanone oxime), were synthesized by Zn(II) acetate tetrahydrate or Cu(II) nitrate trihydrate with based ligand HL1 (2-(2-phenoxy)-4-methyl-1,2-quinazoline-N3-oxide, H is the deprotonate hydrogen) originally. HL1 and both complexes were characterized by elemental analyses and spectroscopic methods, as well as were confirmed by single-crystal X-ray crystallography. It was revealed that two complexes had 2:2 ligand-to-metal ratios and 1 was hexa-coordinated whereas 2 was penta-coordinated. In the crystal structures, HL1 showed a chain-like, while complexes showed 2-D network stacking constructions, and both complexes further formed a 3-D supramolecular structure. The frontier molecular orbital energy of all compounds was calculated, and TD-DFT calculations were performed to analyze the electronic transitions of HL1 and both complexes. Additionally, the structural optimization and electronic transitions of the molecules were obtained via DFT calculations, molecular electrostatic potential (ESP), Hirshfeld surface analysis (HSA), and two-dimensional fingerprint (2D-FP), supporting X-ray diffraction results with the existence of the H···H and C/O···H bonds as the main interactions in the crystal lattice. Especially, cyclic voltammetry (CV) and electron paramagnetic resonance (EPR) spectroscopy properties of 2 were further analyzed. In terms of biological applications, all compounds were investigated for antibacterial activity, and the results displayed two complexes had the best antibacterial performance than others.

Synthesis, Crystal Structure, and Hirshfeld Surface Analysis of a Dinuclear Copper Complex with Pyrazole

Synthesis, Crystal Structure, and Hirshfeld Surface Analysis of a Dinuclear Copper Complex with Pyrazole

Dinuclear copper(II) complexes bridged with acetate and nitrate anions: Study of protein binding and in-vitro anticancer activity

Two dinuclear copper(Ⅱ) complexes [Cu(L)(μ-AcO)2]2·H2O (1) and [Cu(L)(bpy)(μ-NO3)]2. (ClO4)2 (2) were synthesized with the ligand L = N-(3-pyridyl)-1,8-naphthalimide (where, OAc = Acetate, bpy = 2,2′-bipyridine). The complexes were characterized with FT-IR, UV–vis, fluorescence, EPR, and single crystal X-ray diffraction technique. Complex 1 contains two copper(Ⅱ) units bridged by four acetate ions via oxygen atoms having distorted square pyramidal geometry around both the copper(Ⅱ) centers. Complex 2 consists of two copper(Ⅱ) centers with two bridging nitrates via oxygen atoms in a distorted square pyramidal environment. The complexes 1 and 2 efficiently bind to BSA (bovine serum albumin) showing a dynamic quenching mechanism. The in-vitro anticancer activity have been investigated against HeLa cell lines using MTT assay. Complex 1 is two times more active than cisplatin under the same experimental conditions, whereas complex 2 is twelve times more active.