Dinuclear Metal Complexes Research Articles

Dinuclear metal complexes: multifunctional properties and applications.

The development of metal complexes for optoelectronic applications is a fertile area of research. In contrast to the rigorous development of mononuclear metal complexes, dinuclear species have been less well studied and their fundamental chemistry and applications are under-explored. However, dinuclear species present special properties and functions compared with mononuclear species as a consequence of tuning the bridging ligands, the cyclometalated ligands or the two metal centers. More recently, dinuclear species have enabled important breakthroughs in the fields of OLEDs, photocatalytic water splitting and CO2 reduction, DSPEC, chemosensors, biosensors, PDT, smart materials and so on. Here we present an overview of recent developments of dinuclear metal complexes, their multifunctional properties and their various applications. The relationship between structure and property of dinuclear species and important factors which influence device performance are discussed. Finally, we illustrate some challenges and opportunities for future research into dinuclear metal complexes. This review aims to provide an up-to-date summary and outlook of functional dinuclear metal complexes and to stimulate more researchers to contribute to this exciting interdisciplinary field.

Exploratory studies on azido-bridged complexes (Ni2+ and Mn2+) as dual colourimetric chemosensors for S2- and Ag+: combined experimental and theoretical outcomes with real field applications.

We report two isostructural dinuclear transition metal complexes [M2(HL)2(N3)4], where M = Ni2+ (BS-1), Mn2+ (BS-2), and HL is (2-methyl-2-((pyridin-2-ylmethyl)amino)propan-1-ol) and investigate them as molecular sensors towards hazardous entities. BS-1 shows high selectivity towards the S2- and Ag+ ions, easily observed by the naked eye colour change and its detection limit in aqueous solutions for the S2- ion was calculated as 0.55 μM with a binding constant of 3.28 × 105 M-1, while the limit for the Ag+ ion is 21.8 μM. Notably, BS-2 shows good selectivity towards the Ag+ ion with a detection limit of 10.84 μM. Spectroscopic and DFT studies shed light on the mechanistic course of interaction between the host and guest entities, suggesting a sulphide-mediated reduction of the azide mechanism. In a nutshell, these simple transition metal complexes were exploited for discriminately detecting hazardous analytes with real field applications in analytical science (via. "Dip-Stick" approach) as well as engineering science, which provides a significant contribution in the recent advancement of supramolecular chemistry.

Synthesis and Catalytic Activity of Dinuclear Rare-Earth Metal Complexes with Nitrogen-Containing Bridged Dipyrrolyl Ligand towards Ring-Opening Polymerization of e-Caprolactone

Synthesis and Catalytic Activity of Dinuclear Rare-Earth Metal Complexes with Nitrogen-Containing Bridged Dipyrrolyl Ligand towards Ring-Opening Polymerization of <i>e</i>-Caprolactone

Luminescence spectral analysis for Eu(III), and the dinuclear (Zn(II), Cu(II)) complexes with organic ligands by quantum chemical methods

We are very interested in elucidating the theoretical reason why the luminescence of Eu(III)-organo-ligand complexes is enhanced in the presence of Zn(II)-Schiff base complexes, or quenched in the addition of Cu(II) ones. The reason for luminescence enhanced and quenching spectra is deduced from the dynamic (time-dependent) and static (time-independent) standpoints. In the dynamic behavior, we describe that such luminescence spectra depend upon the lifetimes of electron populations at the excited state for their metal-complexes by considering experimental investigations of Eu(III), Zn(II), Cu(II), and dinuclear Eu(III)-(Zn(II), or Cu(II)) complexes with organo-ligands. We also consider the chemical rate equations to form the dinuclear metal complexes, and derive the new equation for the ratio of quantum yields to estimate lifetimes of the Zn(II)- and Cu(II)-saltn complexes. From the static viewpoint, electronic states of septet Eu(III) (as an electron donor), singlet Zn(II) {(or doublet Cu(II)) as an electron acceptor}, and the dinucleus septet Eu(III)⋅Zn(II) (or octet Eu(III)⋅Cu(II)) complexes with organo-ligands are calculated by using DFT and TD-DFT methods. We discuss that the simulated UV–Vis spectra in the range of 450–700 nm reflect to the enhanced Eu(III)⋅Zn(II) and quenching Eu(III)⋅Cu(II) peaks with the experimental ones.

Multiply charged energetic metal ion emissions from dinuclear metal complex exposed to intense femtosecond laser fields

Coulomb explosion of nonmetal ions emerged from a variety of molecules has been studied and utilized for the determination of molecular structure and reaction dynamics. In contrast, Coulomb explosion of metal ions, particularly the large Coulombic interactions are expected, has not yet been explored. In this study, the angular distributions of Mnx+ (x = 1–5), Cy+ (y = 1–4), and Oz+ (z = 1–3) emerged from dimanganese decacarbonyl, in which two metal atoms are sandwiched by axial ligands, exposed to intense femtosecond laser fields (1 × 1014–3 × 1015 W cm−2) are investigated. Manganese ions are produced at relatively low laser intensity compared with other transition metal ions with the same charge number but emerged from mononuclear complexes such as metallocenes and metal hexacarbonyls. The kinetic energies of Mn4+ and Mn5+ are described by the simple Coulomb repulsion model of manganese dimer ion. Fairly high kinetic energy of oxygen and carbon ions compared with those emerged from metal hexacarbonyls strongly suggests that atomic ions originating in ligands are repelled by manganese ions at the moment of Coulomb explosion. The use of dinuclear metal complex is advantageous in the production of multiply charged metal ions accompanying high kinetic energy since two manganese ions are in close confinement due to the repulsions with axial ligand (atomic) ions.

Highly Selective Synthesis of Iridium(III) Metalla[2]catenanes through Component Pre-Orientation by π⋅⋅⋅π Stacking.

A series of molecular metalla[2]catenanes featuring Cp*Ir vertices have been prepared by the template-free, coordination-driven self-assembly of dinuclear iridium acceptors and 1,5-bis[2-(4-pyridyl)ethynyl]anthracene donors. The metalla[2]catenanes were formed by using a strategically selected linker type that is capable of participating in sandwich-type π-π stacking interactions. In the solid state, the [2]catenanes adopt two different configurations depending on the halogen atoms at the dinuclear metal complex bridge. Altering the solvent or the concentration, as well as the addition of guest molecules, enabled controlled transformations between metalla[2]catenanes and tetranuclear metallarectangles.

Isolable Cu(I) Complexes of Extremely Electron-Poor, Completely Unreduced o-Quinone and “Di-o-Quinone” Ligands Stabilized through π–π Interactions in the Secondary Coordination Sphere

The copper-quinone interaction plays important roles in diverse fields such as biochemistry, catalysis, and optically/magnetically switchable materials. Despite this fact, the isolation and thorough characterization of copper(I)-quinone complexes remains a highly challenging task owing to their intrinsic instability. We herein present systems where the stability imparted by the extended π-system of a pyrene ring is used to synthesize, isolate, and crystallographically characterize the first example of a dinuclear metal complex that is bridged by a completely unreduced "di- o-quinone"-type ligand. Additionally, we present the monocopper counterpart with the o-quinone-pyrene type of ligand. The copper complexes are redox-rich and display intriguing electrochemical, optical, and electron paramagnetic resonance (EPR) spectroscopic properties. The line-rich EPR spectra of the one-electron reduced copper(I) complexes were simulated and analyzed via density functional theory calculations. The results presented here establish π-π stacking as a viable alternative to stabilize otherwise unstable redox-active compounds with possible consequences for sensing and redox catalysis.

Silver(I) coordination polymers from dinucleating naphthyridine ligands

Two novel crystalline silver(I) coordination polymers have been synthesized and structurally characterized, using naphthyridine-based ligands that are typically expected to produce dinuclear metal complexes. Electrical conductivity studies on polycrystalline samples show that structural differences in the polymers lead to different conductivity values. These results highlight the flexible coordination chemistry of d10 silver(I) centers, as well as the challenges of ligand design when targeting well-defined multinuclear silver complexes.

Biomimetic catalytic oxidative coupling of thiols using thiolate-bridged dinuclear metal complexes containing iron in water under mild conditions

A green approach to disulfidesviaaerobic oxidative coupling of thiols was developed with a thiolate-bridged heteronuclear complex in water.

Guest encapsulations in non-porous crystals of fully fluorinated dinuclear metal complexes with the M2O2 core (M = Fe3+, Co2+, Ni2+).

Two different coordination types of fully fluorinated dinuclear metal complexes, [Fe2L4(OMe)2] and [M2L4(OH2)2] (M = Co2+, Ni2+ and HL = bis(pentafluorobenzoyl)methane), were obtained. All of the complexes form non-porous crystals, which act as hosts for the adsorption of various benzene derivatives, e.g., benzene, toluene, p-xylene, anisole, and small gas molecules, e.g., CO2, O2, and NO. The complex of iron selectively adsorbs NO in high amounts and the complex of cobalt is found to store adsorbed O2.

Linearly Polarized UV Light-Induced Optical Anisotropy of PVA Films and Flexible Macrocycle Schiff Base Ni(II), Cu(II), Zn(II) Dinuclear Complexes

Three dinuclear metal complexes (comprised of six-coordinated nNi2L and five-coordinated nCu2L and nZn2L) were confirmed by means of elemental analysis, UV-vis and IR spectra, and single X-ray crystal structural analysis in a spectroscopic study. The stable structures of these nNi2L, nCu2L, and nZn2L complexes in poly(vinylalcohol) (PVA) films were analyzed using UV-vis spectra. The molecular orientation of hybrid PVA film materials after linearly polarized light irradiation was analyzed to obtain the polarized spectra and dichroic ratio. Among the three materials, nNi2L and nZn2L complexes indicated an increasing optical anisotropy that depended on the flexibility of the complexes. We have included a discussion on the formation of the pseudo-crystallographic symmetry of the components in a soft matter (PVA films).

Polymerization and Copolymerization of Olefins by Double-Decker Type Dinuclear Metal Complex Catalysts

Polymerization and Copolymerization of Olefins by Double-Decker Type Dinuclear Metal Complex Catalysts

Biomimetics of mononuclear and dinuclear Cu(II) and Fe(III) complexes of a newly synthesized piperazyl Mannich base with or without thiocyanate towards catechol

This paper presents the synthesis and characterization of Cu(II) and Fe(III) complexes of a newly synthesized Mannich base N-[4-hydroxy-3-[[4-(pyridin-2-yl)piperazin-1-yl]methyl]phenyl]acetamide. The spectro-analytical techniques employed include 1H, 13C NMR, IR, UV spectroscopy, conductivity measurements, and elemental analysis. Both mononuclear and dinuclear metal complexes were encountered in the study. Utilizing 3,5-di-tert-butyl catechol (3,5-DTBC) as the substrate, catecholase activity of all four complexes was evaluated with the detailed kinetic studies reported. The nature of the bonding of the thiocyanate is discussed based on the observation of νCN (2150–2050 cm−1). All the metal complexes are catalytically active with turn over numbers ranging from 9.47 to 31.86 h−1 in DMF.

Magneto-electronic properties and structural features of unusual bis(μ-aqua) bis(μ-sulfato) bridges in binuclear cobalt-based 4-aminopyridine

In order to improve the relationship between the structure of bridging dinuclear complexes and their magnetic behavior, we did synthesize metal-organic [Co2(μ2-H2O)2(μ2-SO4)2(C5H6N2)4]·2.86(C2H6OS)·2.88(C4H8O) 1. This dinuclear transition metal complex was characterized by infrared and UV–vis spectroscopy as well as single X-ray diffraction. The thermal and magnetic behavior of this complex was studied. Single crystal X-ray diffraction studies confirmed that 1 consists of discrete dinuclear cobalt entities and two free solvent molecules (DMSO, THF). The two cobalt ions are bridged by two water oxygen atoms and two bidentate sulfate groups to form a four bridged dinuclear core. The optical band gap was determined by diffuse reflection spectroscopy to 3.06 eV for an indirect forbidden transition. The magnetic measurements and DFT calculations suggest the presence of ferromagnetic exchange between Co(II) centers with a strong easy-axis anisotropy.

Synthesis, spectral and crystallographic study, DNA binding and molecular docking studies of homo dinuclear Co(II) and Ni(II) complexes

Two homo dinuclear metal complexes with composition [M2(pda)2(H2O)5]·2H2O (M = Ni2+ and Co2+) have been synthesized and characterized by elemental, spectral and thermal analysis (UV–vis, FT-IR, Fluorescence, EPR, and TGA). The structures of complexes 1 and 2 have been determined by single crystal X-ray diffraction studies and the geometry around M(II) ion was elongated distorted octahedral. Binding studies of the complexes 1 and 2 with Ct-DNA was investigated by absorption, fluorescence and viscosity measurements. The experimental results of DNA binding studies were supported by theoretical (molecular docking analysis). DNA binding results reveal that complexes 1 and 2 bind to the minor groove of DNA and are stabilized through hydrogen bonding interactions.

7-Methyl-6-furylpurine forms dinuclear metal complexes with N3,N9 coordination

Abstract Two dinuclear metal complexes bearing the purine derivative 7-methyl-6-furylpurine (1b) as a ligand are reported. In [Ag2(1b)2(DMSO)2](ClO4)2·DMSO and [Cu2(1b)2(NO3)2], two bridging purine derivatives coordinate the two metal ions via their N3 and N9 positions. In the silver(I) complex, the coordination environment of each metal ion is completed by a DMSO ligand, whereas an additional nitrato ligand coordinates to each copper(I) ion. The intramolecular Ag···Ag distance of 3.1069(5) Å is in agreement with the presence of a weak argentophilic interaction, whereas the Cu···Cu distance of 2.9382(4) Å is too long to be indicative of a cuprophilic interaction. The compounds represent the first examples of dinuclear complexes comprising two N3,N9-bridging purine derivatives without any additional bridging ligand.

Reactions of pyridine-2-ethyl/methyl cyclopentadienes with metal carbonyls

Thermal treatment of pyridine-2-ethyl cyclopentadiene (1) with Fe(CO)5 and Ru3(CO)12 gave novel intramolecular C–H activated dinuclear products (3 and 5). In the case of Fe(CO)5, the reaction also afforded the normal bis(cyclopentadienyl) diiron complex (4). However, similar reaction of pyridine-2-methyl cyclopentadiene (2) with Fe(CO)5 and Ru3(CO)12 only afforded the normal bis(cyclopentadienyl) dinuclear metal complexes (7 and 8). For Ru3(CO)12, the reaction also yielded a pendant η1-pyridyl-coordinated product (9). In addition, the reactions of 1 and 2 with Re2(CO)10 formed the corresponding pyridylethyl/pyridylmethyl cyclopentadienyl rhenium tricarbonyl complexes 10 and 11, which further underwent pyridine to rhenium cyclization via photoirradiation to provide the rhenium dicarbonyl complexes 12 and 13. The molecular structures of 3, 5, 6, 7, 8, 9, and 12 were determined by X-ray diffraction.

Computational modeling of the dinuclear metal complexes with di-o-quinones comprising paramagnetic acene linker groups

Abstract The magnetically-active dinuclear metal complexes with previously unstudied di-o-quinone ligands comprising paramagnetic acene linkers have been investigated with the use of density functional theory quantum-chemical calculations (UTPSSh/UB3LYP/6-311++G(d,p)). Two types of linker groups are considered: linear acenes comprising various number of six-membered cycles and polycyclic hydrocarbons containing terminal five-membered rings. In sodium complexes replacement of terminal six-atomic hydrocarbon rings of the acene chain by five-membered cycles results in changing the type of the exchange interactions involving o-semiquinone radical-anions from antiferromagnetic to ferromagnetic. All paramagnetic centers in copper complexes with dicatecholate forms of the redox-active ligands are antiferromagnetically coupled. The performed computational modeling has shown that the nature and strength of the exchange interactions between paramagnetic centers of the compounds under study depend on the structure of the polycyclic hydrocarbon determined by the type of terminal rings and oxidation state of the redox-active moieties.

Selective recognition of HIV RNA by dinuclear metallic ligands

ABSTRACT We describe the development of dinuclear metallic ligands to target specific HIV RNA structures. Two series of dipyridinyl-N bridged dinuclear metal complexes were synthesized in moderate to good yields and their binding activities toward TAR and RRE RNA were studied both experimentally and theoretically. The docking calculation elucidated some structure features in dimetallic complexes that can affect TAR RNA-binding properties.

Dinuclear PhosphoiminoBINOL-Pd Container for Malononitrile: Catalytic Asymmetric Double Mannich Reaction for Chiral 1,3-Diamine Synthesis

A phosphoiminoBINOL ligand was designed to form a dinuclear metal complex that could hold a malononitrile molecule. The dinuclear bis(phosphoimino)binaphthoxy-Pd2(OAc)2 complex catalyzed a double Mannich reaction of N-Boc-imines with malononitrile to give chiral 1,3-diamines with high enantioselectivity. The rational asymmetric catalyst, which smoothly introduces the first coupling product to the second coupling reaction while avoiding the reverse reaction, facilitates the over-reaction into a productive reaction process.