Binuclear Complexes Research Articles

Coordination of Fluorine-Substituted 1,10-Phenanthroline Diphosphonates with Americium(III) and Lanthanides(III): Solvent Extraction, Complexation, XRD, and Theoretical Study.

Hybrid N,O-donor ligands based on 1,10-phenanthroline are a promising class of compounds for processing high-level waste. Here, we synthesized novel phenanthroline-based diphosphonates containing electron-withdrawing fluorine atoms in alkyl substituents. We studied their extraction properties for Am(III) and, for the first time, for the entire series of lanthanides(III). The extraction of nitric acid for these diphosphonates was also studied. It has been shown that replacing one hydrogen atom with a fluorine atom in the ethyl substituent of a diphosphonate leads to a decrease in the affinity of the ligands for metal cations. Replacing two hydrogen atoms leads to a decrease in the affinity of the ligands for both metal cations and protons. But such modifications led to a change in the nature of the extraction of Am(III) and Eu(III) from nitric acid solutions, and as a result, the diphosphonate with two substituted hydrogen atoms retains its extraction properties when extracted from 5 mol/L HNO3. The complexation in solution was studied by using ultraviolet-visible (UV-vis) titration for Nd(NO3)3 and Eu(NO3)3. The study of complexation in solid form using SC-XRD revealed the formation of complexes of the composition LnL(NO3)3, as well as the possibility of the formation of hydrolyzed binuclear complexes [Eu(μ2,κ4-(RO)2P(O)Phen(O)2(OR))(NO3)2]2. Density functional theory (DFT) calculations were performed to gain more insight into coordination properties and describe experimental data. It was shown that introducing fluorine atoms decreases the charge modules for both Nphen and OP═O and decreases the protonation energy.

Precisely Engineering of Ångström‐Scale Dual Single Atom Drive [Co‐O] Spin‐Orbit Coupling to Boost Lithium–Oxygen Batteries Electrocatalysis

AbstractDual‐atom catalysts (DACs) have emerged as a novel area of investigation in lithium–oxygen (Li‐O2) batteries due to their distinctive synergistic mechanisms. However, achieving precise control of the active site structure and unraveling the synergistic effects of bimetallic species remains a significant challenge. Here, the study reports a pre‐encapsulated pyrolysis strategy using a Co‐based Robson‐type binuclear complex as a precursor to mediate the synthesis of dual single‐atom Co (Co‐DAC) with precise angstrom‐scale inter‐site distance configuration, serving as an efficient catalyst for Li‐O2 batteries. The tailored structure induces significant charge redistribution, reducing crystal field splitting energy (ΔO). The high‐spin Co species generate a strong electronic driving force, forming flexible σ and δ‐like bonds with the crucial oxygen intermediate (*O). Simultaneously, enhanced Co‐O spin‐orbit coupling facilitates electron transport along the bridging O‐channel, forming highly active Co‐O‐O‐Co electron chains that synergistically adsorb *O, establishing a favorable reaction pathway. Significant optimization of Li‐O2 batteries redox kinetics is achieved based on the well‐defined local structure of dual single‐atom Co sites. This work enhances the understanding of the dependence between rational design of custom structures and corresponding electron transfer dynamics, while providing new strategies and theoretical guidance for DACs to help develop high‐performance Li‐O2 batteries.

Structural optimization of pyridine quinoxaline cobalt (II) catalysts for MMA polymerization based on systematical SCSC transformation study

The Schiff base condensation reaction was adopted to synthesize a series of pyridine-based quinoxaline ligands (L1, L2, L3, L4) using 2-acetylpyridine and 1,2-phenylenediamine aromatic amines with different substituents of –OCH3, –F, -Cl, -Br. Then, four symmetrical dinuclear metal complexes (1–4) were obtained by coordination reaction of the synthesized ligands with CoCl2·6H2O, and six unexpectedly systematic and novel solvent-involved asymmetric mononuclear metal complexes (1A-4A, 3B, 4B) were obtained during single crystals cultivating by solvent diffusion method. The microscopic composition of the complexes were proved by a series of characterizations such as elemental analysis, IR and UV–vis. At the same time, by improving the single crystal culture technology, full crystal sample of compounds was obtained and X-ray single crystal diffraction showed a rare single crystal to single crystal structure transition (SCSC) phenomenon in this study. Furthermore, the catalytic properties of the complexes for MMA polymerization was explored, it was found that the catalytic activity of complexes 1–4 containing different types of substituents on pyridyl quinoxaline ligand was in the order of 1 < 2 <3 < 4, indicating that the complex with an electron-withdrawing substituent showed the higher activity than that of electron-donating substituent. Complexes 1A-4A, 3B and 4B showed higher catalytic activity in MMA polymerization than 1–4, which confirmed that the catalytic activity of mononuclear complexes were generally higher than that of binuclear complexes.

A multichromotropic dinuclear copper(II) complex: Unveiling its structural and spectroscopic properties

A novel dinuclear copper(II) complex, [Cu₂L₂(μ-Cl)₂]Cl₂•4H₂O, was synthesized using a tetradentate hemilabile ligand, 3,3′-((pyridin-2-ylmethyl)azanediyl)dipropanamide (L). The complex was characterized by various spectroscopic techniques, including FT-IR, UV-Vis spectroscopy, elemental analysis, TG-DTA, and conductivity measurements. X-ray crystallography confirmed the formation of the binuclear complex, revealing a dicationic unit with distorted octahedral geometry at the copper centers, bridged by two chloride ions. The coordination environment around each copper ion includes two nitrogen and two oxygen donors from the ligand, along with the bridging chlorides. Notably, the complex exhibits significant chromotropism, including solvatochromism, halochromism, ionochromism, and thermochromism, which are attributed to the Jahn-Teller effect and the flexible coordination environment around the copper centers. Thermal analysis indicates the stability of the complex up to 118°C, with subsequent decomposition occurring in distinct stages. Hirshfeld surface analysis further elucidates the intermolecular interactions within the crystal lattice. Computational studies were conducted using Time Dependent Density Functional Theory (TD-DFT) to gain insights into the nature of the observed chromotropism. The computed absorption spectra closely matched the experimental data, validating the proposed electronic transitions responsible for the chromotropic behavior. The multifaceted chromotropic behavior of this complex highlights its potential applications in sensing technologies and smart materials. The study advances the understanding of chromotropism in metal complexes and provides insights into the design of responsive materials based on transition metal chemistry.

The Role of Spacers as a Probe in Variation of Photoluminescence Properties of Mono- and Bi-Nuclear Boron Compounds.

A series of N,O donor-based mono- and binuclear four-coordinated boron complexes were synthesized. Depending on the substitution and spacer, these complexes exhibit intense blue, green and yellow emission in solution states. Notably, the fluorescence quantum yields (ΦF) and fluorescence decay (lifetime, τ) of mononuclear boron complexes (2 a-2 e) were higher than the binuclear boron complexes (2 f-2 k). The lowest lifetime and quantum yield in binuclear boron complexes were due to intramolecular rotation induced non radiative processes. The disulphide spacer-based boron complexes 2 i-2 k showed aggregation-caused quenching in the THF/H2O mixture whereas no other complexes were ACQ responsive. These complexes show large Stokes shift, one of them i. e. 2 e has the highest Stokes shift of 130 nm. Further, the electrochemical study suggests the presence of two redox incidences. Theoretical studies show close corroboration between the TD-DFT computed and experimentally measured absorption maxima as well as DFT (GIAO) calculated and experimentally measured 11B NMR values. This complements the appropriate selection of the theoretical methods to shed light on the electronic transitions in the mono- and binuclear BF2 complexes.

Incorporation of a Binuclear Cobalt Complex into MOFs for Photocatalytic CO2 Reduction with H2O as an Electron Donor.

The development of molecular composite photocatalysts for cost-effective, sacrificial-reagent-free CO2 reduction is desirable but challenging. Herein, we employed an in situ encapsulation strategy to encapsulate the binuclear cobalt complex (Co2L) within NH2-MIL-125 and synthesized a range of MOF-based composites with varying cobalt content for photocatalytic CO2 reduction. The photocatalytic results showed that the catalytic performance increased with the increase in Co2L content, reaching a rapid CO generation rate of 27.95 μmol·g-1·h-1, over 5 times that of bare NH2-MIL-125, with water as the electron donor instead of any organic sacrificial agent. This composite catalyst effectively harnesses the advantages of both molecular catalysts and MOFs, leveraging the superior catalytic activity of molecular catalysts while also capitalizing on the light absorption and water oxidation capabilities of MOFs, resulting in a remarkable ability for photocatalytic CO2 reduction. The photocatalytic mechanism involving electron transfer and CO2 activation has been revealed by photoluminescence spectroscopy, in situ X-ray photoelectron spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy, and other control experiments.

Integrated Design of Homogeneous/Heterogeneous Copper Complex Catalysts to Enable Synergistic Effects on Sulfur and Lithium Evolution Reactions.

Fatal polysulfide shuttling, sluggish sulfur redox kinetics and detrimental lithium dendrites have curtailed the real discharge capacity, working lifespan and safety of lithium-sulfur (Li-S) batteries. Organic small molecule promotors as one type of emerging active catalysts can fulfil the management of the electrochemical species evolution behaviors. Herein, an integrated engineering is organized by synthesizing dual chlorine-bridge enabled binuclear copper complex (Cu2(phen)2Cl2) and its derivative generated in electrolyte (Cu-ETL) as the heterogeneous and homogeneous catalyst, respectively. The well-designed Cu-ETL with a optimized concentration of 0.25 wt% as a homogeneous enabler offers highly utilized Cu centers and the sufficient interface contact for guiding the Li2S nucleation/decomposition reactions. The Cu2(phen)2Cl2 loaded on carbon spheres as an interlayer (Cu-INT) can break through the catalytic limitation resulting from the saturated concentration of Cu-ETL and thus offers an extended manipulation effect. Benefiting from the synergistic effect, the Li-S battery shows stable cycling at 3 C upon 500 cycles with a capacity degradation rate as low as 0.029 % per cycle. Of specific note, an actual cell energy density of 372.1 Wh kg-1 is harvested by a 1.2 Ah-level soft-packaged pouch cell, implying a chance for requiring the demand of high-energy batteries.

Integrated Design of Homogeneous/Heterogeneous Copper Complex Catalysts to Enable Synergistic Effects on Sulfur and Lithium Evolution Reactions

AbstractFatal polysulfide shuttling, sluggish sulfur redox kinetics and detrimental lithium dendrites have curtailed the real discharge capacity, working lifespan and safety of lithium−sulfur (Li−S) batteries. Organic small molecule promotors as one type of emerging active catalysts can fulfil the management of the electrochemical species evolution behaviors. Herein, an integrated engineering is organized by synthesizing dual chlorine‐bridge enabled binuclear copper complex (Cu2(phen)2Cl2) and its derivative generated in electrolyte (Cu‐ETL) as the heterogeneous and homogeneous catalyst, respectively. The well‐designed Cu‐ETL with a optimized concentration of 0.25 wt% as a homogeneous enabler offers highly utilized Cu centers and the sufficient interface contact for guiding the Li2S nucleation/decomposition reactions. The Cu2(phen)2Cl2 loaded on carbon spheres as an interlayer (Cu‐INT) can break through the catalytic limitation resulting from the saturated concentration of Cu‐ETL and thus offers an extended manipulation effect. Benefiting from the synergistic effect, the Li−S battery shows stable cycling at 3 C upon 500 cycles with a capacity degradation rate as low as 0.029 % per cycle. Of specific note, an actual cell energy density of 372.1 Wh kg−1 is harvested by a 1.2 Ah‐level soft‐packaged pouch cell, implying a chance for requiring the demand of high‐energy batteries.

Coordination Compounds of Alkali and Rare Earth Metals Based on Centrosymmetric Chlorine-Substituted Bis-Mercaptooxazole. Synthesis, Structure, and Luminescence

New coordination polymers were synthesized. A ditopic centrosymmetric organic ligand containing oxazole heterocycles, 4,8-dichlorobenzo[1,2d:4,5d´]bis(oxazole)-2,6(3H,7H)-dithione (H2L), was prepared and structurally characterized. It was shown that deprotonated H2L forms non-luminescent binuclear molecular complexes Li2L(THF)6 (I) and Na2L(DME)4 (II) with alkali metals, while complexes of H2L with lanthanides are ionic compounds [Ln(DMSO)8][L]1.5 (Ln = Nd (III), Yb (IV)) exhibiting moderate metalcentered emission in the near-infrared (IR) range, despite the absence of coordination of the ligand L to lanthanide ions. The molecular structures of H2L·2DMSO and I–III were established by X-ray diffraction (CCDC no. 2320461 (H2L·2DMSO), 2320462 (I), 2320463 (II), 2320464 (III)).

Isothermal conversion of methane to methanol over Cu-CHA using different oxidants

Methane oxidation to methanol in cyclic processes using CuO-zeolites has traditionally employed O2 and N2O as oxidants. This study explores the use of Cu-CHA zeolite, demonstrating that CO2 can substitute O2 in an isothermal reaction at 400 °C, analogous to previous findings using Cu-MAZ. The use of in situ UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and density functional theory (DFT) theoretical calculations identified the formation of a binuclear copper hydroxide complex, Z-[CuOH-HOCu]2+-Z, on the Cu-CHA. Initial treatment using CO2 led to marginally superior catalytic activity, compared to the use of O2 alone, indicating the stability of the Z-[CuOH-HOCu]2+-Z complex against self-reduction at 400 °C. In subsequent cycles, activation with O2 facilitated the oxidation of adsorbed methanol, yielding water and reconstituting the active sites. Conversely, activation with CO2 led to the partial desorption of methanol, precluding water production and subsequent catalyst regeneration. The findings suggested that both O2 and CO2 activations necessitated a post-reaction water extraction step, followed by thermal treatment to replenish the active sites. Importantly, the results indicated that CO2 could be used as a viable alternative oxidant to O2 in this catalytic process, potentially enhancing the sustainability of industrial methanol production.

Binuclear complexes of all first row 3d metals (Sc to Zn) with a cyclic N4-tetradentate ligand: metal-metal bond strengths and bond orders

Metal-metal (MM) bonds in binuclear complexes M2L2 (L = tetradentate ligand) for the first row transition metals are studied using DFT to design novel complexes which mimic lantern complexes having four bidentate ligands. Two orientations for the ligand array are applied − orthogonal (orth) and lateral (lat). Ground states for all complexes are identified from several low-lying spin states, where each orth isomer is generally lower in energy than the corresponding lat isomer. All the MM bonds are assigned formal bond order (fBO) values through MO analysis and/or electron counting. The M2L2orth complexes in many ways mimic the geometrical and electronic structure of known tetragonal lantern complexes. The formal shortness ratio (FSR) and the Wiberg index WMM for the MM bond correlate well with the fBO values, validating their use as measures of intrinsic MM bond strength.

Design of dinuclear osmium complex doped antifouling cellulose nanoparticles for targeting and dual photodynamic/photothermal therapy under near infrared irradiation

Transition metal-ligand has been explored in the treatment of tumors in photodynamic theray (PDT) or photothermal therapy (PTT) and Osmium complex attracts attentration due to its lower toxicity and longer absorption wavelength. However, there was no report about binuclear Os complex for combined therapy of PDT and PTT which could have a synergistic effect and improve the effectiveness. Herein, we synthesis of mono/dinuclear Os complexes (OsY1, OsY2) with dual PDT/PTT capabilities under a single near-infrared (NIR) excitation wavelength. These features arise from the large π-conjugated structure of our dinuclear Os complex coupled with efficient metal-to-ligand charge transfer, which bring in ultralow energy gaps of 0.733 eV and 0.308 eV for OsY1 and OsY2, respectively. Furthermore, we prepared the Osmium complex-doped, aptamer-conjugated cellulose NPs via the emulsion polymerization method. These NPs exhibit a notable ability to target mitochondria and posse a “protein corona-free” status, showing much higher efficiency in tumor ablation (76 %) than the commercialized indocyanine green (ICG) doped cellulose NPs (24 %) under 808 nm irradiation. Consequently, our designed mono/dinuclear Os complex, featuring a single-molecule dual PDT/PTT effect within doped antifouling NPs, holds promise for potential applications in cancer therapy.

Luminescence Thermochromism of a Noncluster Copper Iodide Complex.

Hybrid copper(I) halide materials are currently attracting significant attention due to their exceptional luminescence properties, offering great potential for the development of multifunctional emissive materials with, in addition, eco-friendly features. A binuclear copper iodide complex, based on the [Cu2I2L4] motif with phosphite derivatives as ligands, has been synthesized and structurally characterized. Photophysical investigations indicate that this complex displays luminescence thermochromic properties, which are characterized by a temperature-dependent change in the relative intensity of two emission bands. The high-contrast luminescence thermochromism, with an important color variation from purple to cyan, is ascribed to the thermal equilibrium of two different excited states. While thermochromism is relatively known for multimetallic complexes, the perfectly controlled thermochromism of the studied compound is unprecedented for a binuclear complex. From theoretical investigations, this original feature is due to the coordination of phosphite ligands, which induces a specific energy layout of the complex, presenting vacant orbitals of varying nature. This single-component, dual-emissive binuclear complex, displaying relevant sensitivity temperature response, presents great potential for luminescence ratiometric thermometry applications. This study underlines the relevance of the ligand engineering strategy in developing original, emissive, and sustainable copper-based materials.

Synthesis and evaluation of new mono- and binuclear salen complexes for the Cα-alkylation reaction of amino acid substrates as chiral phase transfer catalysts

In this study, we present a series of Zn(II) mono- and Cu(II) binuclear salen complexes synthesized and assessed for their effectiveness in the Cα-alkylation reaction. Through systematic experimentation, it was observed that the introduction of a methoxy group at position 3 of the phenyl group in the salicylidene ligand led to a notable enhancement in asymmetric yield, while an allyl group reduced yield. Computational DFT calculations supported the involvement of the binuclear complex in the transition state of the reaction, elucidating the underlying mechanisms governing the observed catalytic behavior. A newly synthesized binuclear complex exhibited significantly higher catalytic activity compared to its mononuclear counterpart which could potentially be explained by increased intramolecular rigidity. This comprehensive investigation not only advances our understanding of structure-activity relationships in chiral salen complexes but also provides valuable insights for the rational design and optimization of catalysts for the asymmetric Cα-alkylation reaction.

The first type of binuclear copper complex with terminal sulfide: synthesis, structural characterization, and cytotoxicity evaluation

A novel copper complex of [CuII (μ2–S)(terminal-S)(2-acetylpyrdine oxime)2 (1) is synthesized and characterized by X-ray single-crystal diffraction. The free ligand of 2-acetylpyrdine oxime is an unexpected product obtained from a condensation reaction of p-aminobenzene sulfonamide and 2-acetylpyridine and is characterized by IR, 1HNMR, and 13CNMR spectroscopic methods. X-ray crystallography showed strictly planar bridged μ2- Cu2(S)2 core, and each copper(II) center exhibits distorted square pyramidal coordination geometry. The cytotoxicity of the complex was tested in vitro against esophageal cancer (SKGT-4) cell lines by metabolic tests, using 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide as a reagent. Complex 1 showed a remarkable inhibition response in SKGT-4 cell lines.

Neutral water-soluble µ-S nitrosyl iron complex with acetylcysteine non-silent in EPR spectra

The water-soluble neutral binuclear nitrosyl iron complex with N-acetyl-L-cysteine was synthesized. As follows from X-ray analysis, the complex crystallizes in the monoclinic crystal system, space group P2(1). The distance between iron atoms is 2.7 Å The complex belongs to Roussin's red salt esters (RRE) and is expected to be diamagnetic. However, in the EPR-spectrum there is a broad line with a g-factor of 2.010, which disappears upon the dissolution of the complex in water or alcohol. However, dissolution of the complex in DMSO leads to an increase in the classical signal for mononuclear nitrosyl iron complex with a g-factor of 2.03. The IR-spectrum of the crystalline sample of the complex shows an atypical pattern among RREs. This behaviour was studied with quantum-chemical calculations. The magnetic properties of the complex are also unusual for a complex of this structural type. The complex was also studied by Mössbauer and UV-spectroscopy.

Eu(III) complexes derived from 2-quinolinecarbohydrazide Schiff base ligand, relations between structure and luminescence properties

A series of Eu(III) complexes were obtained following the template condensation of 2-quinolinecarbohydrazide and 2,6-diacetylpyridine, namely: [Eu(H2pbqh)(NO3)3]·MeOH (1), [Eu(Hpqh)(NO3)3]·2MeCN (2), [Eu(H2pbqh)(SCN2)(MeOH)2](SCN) (3) and [Eu2(pbqh)2(NO3)2(H2O)2]·2.5MeOH (4). The structures of complexes and a new H2pbqh ligand (N',N'''-((1E,1′E)-pyridine-2,6-diylbis(ethan-1-yl-1-ylidene))bis(quinoline-2- carbohydrazides)) were elucidated by single-crystal X-ray diffraction. H2pbqh coordinate pentadentate ONNNO and forms mononuclear complexes 1 and 3. The bis-deprotonated ligand pbqh2- act as hexadentate/bridging mode generates the binuclear complex in 4. The partially condensed ligand Hpqh, tetradentate ONNO, was recorded in complex 2. The crystallographic results reveals that the coordinated H2pbqh/Hpqh ligands and Eu3+ cation form a planar structure in these complexes and nitrate anions coordinate chelate, completing the coordination sphere of Eu3+. The solid state photoluminescent emission was investigated highlighting the nitrate complexes 1 and 2 that exhibit red intense luminescence (λmax = 618 nm). Moreover, the computational calculations reveal different pathways of energy transfer from ligand to Eu3+ electronic states explaining the luminescent behavior.

Antifungal Activity of Some New Binuclear Complexes

Three complexes of copper(II) and iron(II) with mixed ligands acetylacetonebis(thio-semicarbazone)- ABTSH2 and benzaldazine- BA have been prepared and characterized using different physico-chemical techniques including the determination of metal contents, mole-cular weight, measurement of molar conductivity, magnetic moment, molar refraction, infrared and electronic spectra. Accordingly, octahedral complexes having general formulaes [Cu2(ABTSH2)2(BA)2Cl2]Cl2 and [M2(ABTSH2)2(BA)2(SO4)2] {M= Cu(II) or (Fe(II)} have been proposed. The resulted complexes screened for antifungal activity in vitro against the citrus pathogen Aspergillus niger and Fusarium sp. which caused root rot of sugar and the beans pathogen Alternaria sp. All the complexes exhibited significant antifungal activities against these pathogens. The antifungal activity of these complexes were comparable with the standard fungicides in ethanol. The complex [Cu2(ABTSH2)2(BA)2Cl2]Cl2 had the best antifungal activity against Alternaria sp.

Double-stranded binuclear helical complexes of 5,5’-bisdiazo-dipyrromethane with Zn(II): synthesis, structures, photophysical properties, and DFT calculations

The reaction of two 5,5΄-bisdiazo-dipyrromethane compounds (H2L1 and H2L2 ) with ZnCl2 afford two Zn(II) complexes (Zn2L1 2 and Zn2L2 2 ). The X-ray crystallographic studies revealed that both complexes were double-stranded binuclear helicates. Each Zn(II) ion was coordinated to four nitrogen atoms of two azopyrrole units from two ligands in a distorted tetrahedral geometry. Due to the existence of the hydroxyl groups, the Zn2 L 2 2 complex self-assembled into a two-fold interpenetrating grid structure through O-H…O and N-H…O hydrogen bonds. Zn2 L 2 1 and Zn2 L 2 2 displayed intense absorptions at 439 and 446 nm and shoulder peaks at 486 and 497 nm, respectively. Both complexes were also weakly fluorescent with a fluorescence band at 602 nm. DFT calculations revealed that the hydroxyl group can destabilize the frontier molecular orbitals and decrease the energy gap (ΔE), and finally caused Zn2 L 2 2 higher HOMO and LUMO orbital levels, smaller energy gap (ΔE), and longer λmax absorption than Zn2 L 2 1 .

Synthesis, Structure, and Biological Activity of Binuclear Mixed-Ligand Complexes of Nickel(II) Benzoylhydrazone 2-(N-Tosylamino)Benzaldehyde

Synthesis, Structure, and Biological Activity of Binuclear Mixed-Ligand Complexes of Nickel(II) Benzoylhydrazone 2-(N-Tosylamino)Benzaldehyde