Dinuclear and tetranuclear complexes of copper coordinated by an anthracene-based new μ-bis(tridentate) ligand: Synthesis, structure, spectroscopy and magnetic properties

Halide mediated modulation of magnetic interaction and anisotropy in dimeric Co(II) complexes

The burgeoning interest in the field of molecular magnetism is to perceive the high magnetic anisotropy in different geometries of metal complexes and hence to draw a magneto-structural correlation. Despite a handful of examples to exemplify the magnetic anisotropy in various coordination geometries of mononuclear complexes, the magnetic anisotropies for two different coordination geometries are underexplored. Employing an appropriate synthetic strategy utilizing the ligand LH2 [2,2'-{(1E,1'E)-pyridine2,6-diyl-bis(methaneylylidine)}-bis(azaneylylidine)diphenol] and cobalt halide salts in a 1 : 2 stoichiometric ratio in the presence of triethylamine allowed us to report a new family of dinuclear cobalt complexes [CoII2X2(L)(P)(Q)]·S with varying terminal halides [X = Cl, P = CH3CN, Q = H2O, S = H2O (1), X = Br, P = CH3CN, Q = H2O, S = H2O (2), X = I, P = CH3CN, and Q = CH3CN (3)]. All these complexes are characterized through single crystal X-ray crystallography, which reveals their crystallization in the monoclinic system P21/n space group with nearly identical structural features. These complexes share vital components, including Co(II) centers, a fully deprotonated ligand [L]2-, halide ions, and solvent molecules. The [L]2- ligand contains two Co(II) centers, where phenolate oxygen atoms bridge the Co(II) centers, forming a Co2O2 four-membered ring. Co1 demonstrates a distorted pentagonal-bipyramidal geometry with axial positions for solvent molecules, while Co2 displays a distorted tetrahedral geometry involving phenolate oxygen atoms and halide ions. Temperature-dependent dc magnetic susceptibility measurements were conducted on 1-3 within a range of 2 to 300 K at 1 kOe. The χmT vs. T plots exhibit similar trends, with χmT values at 300 K higher than the spin-only value, signifying a significant orbital contribution. As the temperature decreases, χmT decreases smoothly in all the complexes; however, no clear saturation at low temperatures is observed. Field-dependent magnetization measurements indicate a rapid increase below 20 kOe, with no hysteresis and a low magnetic blocking temperature. DFT and CASSCF/NEVPT2 theoretical calculations were performed to perceive the magnetic interaction and single-ion anisotropies of Co(II) ions in various ligand-field environments.

Design, Synthesis and Evaluation of a Series of Zinc(II) Complexes of Anthracene-Affixed Multifunctional Organic Assembly as Potential Antibacterial and Antibiofilm Agents against Methicillin-Resistant Staphylococcus aureus

A novel class of zinc(II)-based metal complexes, i.e., [Zn₂(acdp)(μ-Cl)]·2H₂O (1), [Zn₂(acdp)(μ-NO₃)]·2H₂O (2), and [Zn₂(acdp)(μ-O₂CCF₃)]·2H₂O (3) (Cl^- = chloride; NO₃^- = nitrate; CF₃CO₂^- = trifluoroacetate) of anthracene-affixed multifunctional organic assembly, H₃acdp (H₃acdp = N,N'-bis[anthracene-2-ylmethyl]-N,N'-bis[carboxymethyl]-1,3-diaminopropan-2-ol), have emerged as promising antibacterial and antibiofilm agents in the domain of medicinal chemistry. Accordingly, complexes 1-3 were synthesized by utilizing H₃acdp in combination with ZnCl₂, Zn(NO₃)₂·6H₂O, and Zn(CF₃CO₂)₂·H₂O respectively, in the presence of NaOH at ambient temperature. The complexation between H₃acdp and Zn²⁺ was delineated by a combined approach of spectrophotometric and spectrofluorometric titration studies. The stoichiometry of acdp^3-/Zn²⁺ in all three complexes is observed to be 1:2, as confirmed by spectrophotometric/spectrofluorometric titration data. Elemental analysis (C, H, N, Zn), molar conductance, FTIR, UV-vis, and thermoanalytical (TGA/DTA) data were effectively used to characterize these complexes. Besides, the structures of 1-3 were established by density functional theory (DFT) calculation using B3LYP/6-311G, specifying a self-assembled compact geometry with average Zn···Zn separation of 3.4629 Å. All three zinc complexes exhibited significantly high antibacterial and antibiofilm activity against methicillin-resistant Staphylococcus aureus (MRSA BAA1717). However, complex 1 showed a more recognizable activity than 2 and 3, with minimum inhibitory concentration (MIC) values of 200, 350, and 450 μg/mL, respectively. The antimicrobial activity was tested by employing the minimum inhibitory concentration (MIC) and time-kill assay. The crystal violet (CV) assay and microscopic study were performed to examine the antibiofilm activity. As observed, complexes 1-3 had an effect on the production of extracellular polymeric substance (EPS), biofilm cell-viability, and other virulence factors such as staphyloxanthin and hemolysin production, autoaggregation ability, and microbial cell-surface hydrophobicity. Reactive oxygen species (ROS) generated due to inhibition of staphyloxanthin production in response to 1-3 were also analyzed. Moreover, complexes 1-3 showed an ability to damage the bacterial cell membrane due to accumulation of ROS resulting in DNA leakage. In addition, complexes 1-3 displayed a synergistic/additive activity with a commercially available antibiotic drug, vancomycin, with enhanced antibacterial activity. On the whole, our investigation disclosed that complex 1 could be a promising drug lead and attract much attention to medicinal chemists compared to 2 and 3 from therapeutic aspects.

Exploring a new family of designer copper(II) complexes of anthracene-appended polyfunctional organic assembly displaying potential anticancer activity via cytochrome c mediated mitochondrial apoptotic pathway

The present article describes the systematic study on design and synthesis, physicochemical properties and spectroscopic features, and potential anticancer activities of a family of novel copper(II)-based designer metal complexes [Cu₂(acdp)(μ-Cl)(H₂O)₂] (1), [Cu₂(acdp)(μ-NO₃)(H₂O)₂] (2) and [Cu₂(acdp)(μ-O₂CCF₃)(H₂O)₂] (3) of anthracene-appended polyfunctional organic assembly, H₃acdp (H₃acdp = N,N'-bis[anthracene-2-ylmethyl]-N,N'-bis[carboxymethyl]-1,3-diaminopropan-2-ol). Synthesis of 1-3 was accomplished under facile experimental conditions, preserving their overall integrity in solution. The incorporation of polycyclic anthracene skeleton within the backbone of organic assembly increases lipophilicity of resulting complexes, thereby dictating the degree of cellular uptake with improved biological activity. Complexes 1-3 were characterized by elemental analysis, molar conductance, FTIR, UV-Vis absorption/fluorescence emission titration spectroscopy, PXRD and TGA/DTA studies, including DFT calculations. The cellular cytotoxicity of 1-3 when studied in HepG2 cancer cell line showed substantial cytotoxic effects, whereas no such cytotoxicity was observed when exposed to normal L6 skeletal muscle cell line. Thereafter, the signaling factors involved in the process of cytotoxicity in HepG2 cancer cells were investigated. Alteration of cytochrome c and Bcl-2 protein expression levels along with modulation of mitochondrial membrane potential (MMP) in the presence of 1-3, strongly suggested the possibility of activating mitochondria-mediated apoptotic pathway involved in halting the cancer cell propagation. However, when a comparative assessment on their bio-efficacies was made, 1 showed higher cytotoxicity, nuclear condensation, DNA binding and damage, ROS generation and lower rate of cell proliferation compared to 2 and 3 in HepG2 cell line, indicating that the anticancer activity of 1 is significantly higher than that of 2 and 3.

Tetranuclear copper(II) complex of 2-hydroxy-N,N′-bis[1-(2-hydroxyphenyl)ethylidene]propane-1,3-diamine

In the title Schiff base tetra­nuclear copper(II) complex, two discrete environments are present in the structure: CuNO₄ and CuNO₃. Two copper(II) cations are situated in distorted square-pyramidal environment, while two copper(II) cations are located in a slightly square-planar geometry. One bridging acetate group acting in an η¹:η¹-μ₂-mode connects two copper(II) ions, while another bridging acetate group connects three copper(II) ions in an η¹:-η²–μ₃-mode.

The title mol­ecular structure, namely, (μ₃-acetato)(μ₂-acetato)­bis­(μ₃-1,3-bis­{[1-(2-oxidophen­yl)ethyl­idene]amino}­propan-2-olato)tetra­copper(II) monohydrate, [Cu₄(C₁₉H₁₉N₂O₃)₂(CH₃CO₂)₂]·H₂O, corresponds to a non-symmetric tetra­nuclear copper complex. The complex exhibits one ligand mol­ecule that connects two copper Cu^II metal centres via its ethano­lato oxygen anion acting in a μ₂-mode and one ligand mol­ecule that connects three copper Cu^II metal centres via its ethano­lato oxygen anion acting in a μ₃-mode. One bridging acetate group acting in an η¹:η¹-μ₂-mode connects two copper(II) ions while another bridging acetate group connects three copper(II) ions in an η¹:-η²-μ₃-mode. A chair-like Cu₃O₃ structure is generated in which the two CuO₄N units are connected by one μ₂-O ethano­late oxygen atom. These two units are connected respectively to the CuO₃N unit via one μ₃-O ethano­late oxygen atom and one μ₂-O atom from an acetate group. The μ₃-O atom also connects one of the CuO₄N units and the CuO₃N unit to another CuO₃N unit, which is out of the chair-like structure. Each of the two penta­coordinated Cu^II cations has a distorted NO₄ square-pyramidal environment. The geometry of each of the two CuNO₃ units is best described as a slightly square-planar environment. A series of intra­molecular O—H⋯O hydrogen bonds is observed. In the crystal, the units are connected by inter­molecular C—H⋯O and O—H⋯O hydrogen bonds, thus forming sheets parallel to the ac plane

Inorganic Phosphate and Arsenate within New Tetranuclear Copper and Zinc Complexes: Syntheses, Crystal Structures, Magnetic, Electrochemical, and Thermal Studies

Three, PO₄ ^3-/HPO₄ ^2- and AsO₄ ^3--incorporated, new tetranuclear complexes of copper(II) and zinc(II) ions have been synthesized and fully characterized. In methanol-water, reactions of H₃cpdp (H₃cpdp = N,N'-Bis[2-carboxybenzomethyl]-N,N'-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol) with copper(II) chloride in the presence of either NaOH/Na₂HPO₄·2H₂O or KOH/Na₂HAsO₄·7H₂O lead to the isolation of the tetranuclear complexes Na₃[Cu₄(cpdp)₂(μ₄-PO₄)](OH)₂·14H₂O (1) and K₂[Cu₄(cpdp)₂(μ₄-AsO₄)](OH)·16²/₃H₂O (2), respectively. Similarly, the reaction of H₃cpdp with zinc(II) chloride in the presence of NaOH/Na₂HPO₄·2H₂O yields a tetranuclear complex, Na(H₃O)₂[Zn₄(cpdp)₂(μ₄-HPO₄)]Cl₃·12¹/₂H₂O (3). All complexes are characterized by single-crystal X-ray diffraction and other analytical techniques, such as Fourier transform infrared and UV-vis spectroscopy, thermogravimetric and electrochemical studies. The solid-state molecular framework of each complex contains two monocationic [M₂(cpdp)]⁺ (M = Cu, Zn) units, which are exclusively coordinated to either phosphate/hydrogen phosphate or arsenate groups in a unique mode. All three complexes exhibit a μ₄:η¹:η¹:η¹:η¹ bridging mode of the PO₄ ^3-/HPO₄ ^2-/AsO₄ ^3- groups, with each bridging among four metal ions. The thermal properties of all three complexes have been investigated by thermogravimetric analysis. Low-temperature magnetic studies of complexes 1 and 2 disclose moderate antiferromagnetic interactions mediated among the copper centers through alkoxide and phosphate/arsenate bridges. Electrochemical studies of complexes 1 and 2 in dimethylformamide using cyclic voltammetry reveal the presence of a fairly assessable one-electron metal-based irreversible reduction and one quasireversible oxidation couple.