Dinuclear Metal Complexes Research Articles

Implementation of 2,2'-azobispyridine radical mono- and dianions in dinuclear rare earth metal complexes.

The seminal isolation of a dinuclear rare earth metal complex comprising a bridging 2,2'-azobispyridyl radical anion, [(Cptet2Y)2(μ-abpy˙)](BPh4), is presented, which was obtained from a one-electron chemical oxidation of [(Cptet2Y)2(μ-abpy)]. The unprecedented compounds were characterized by crystallography, spectroscopy and DFT computations. The radical character was proven by EPR spectroscopy.

Di-μ-adipato-κ4 O 1,O 1':O 6,O 6'-bis-[(2,2'-di-pyridyl-amine-κ2 N,N')zinc(II)] trihydrate.

The title compound, [Zn2(C6H8O4)2(C10H9N3)2]·3H2O or {Zn2[(C5H4N)2NH]2[μ-(CH2)4(COO)2]2}·3H2O, was separ-ated from the solvothermal reaction of zinc(II) sulfate hepta-hydrate, 2,2'-di-pyridyl-amine and sodium adipate. The dinuclear metal complex has a centrosymmetric structure, with the ZnII atom adopting a highly distorted octa-hedral coordination sphere composed of four oxygen atoms from bridging adipato ligands and two pyridine nitro-gen atoms. In the crystal, the title compound aggregates into a tri-periodic supra-molecular structure through inter-molecular hydrogen-bonding networks of the form O-H⋯O and N-H⋯O.

Simulating thermodynamic properties of dinuclear metal complexes using Variational Quantum Algorithms

Abstract In this paper, we investigate the use of variational quantum algorithms for simulating the thermodynamic properties of dinuclear metal complexes. Our study highlights the potential of quantum computing to transform advanced simulations and provide insights into the physical behavior of quantum systems. The results demonstrate the effectiveness of variational quantum algorithms in simulating thermal states and exploring the thermodynamic properties of low-dimensional molecular magnetic systems. The findings from this research contribute to broadening our understanding of quantum systems and pave the way for future advancements in materials science through quantum computing.

A Planar-Structured Dinuclear Cobalt(II) Complex with Indirect Synergy for Photocatalytic CO2-to-CO Conversion.

Dinuclear metal synergistic catalysis (DMSC) has been proved an effective approach to enhance catalytic efficiency in photocatalytic CO2 reduction reaction, while it remains challenge to design dinuclear metal complexes that can show DMSC effect. The main reason is that the influence of the microenvironment around dinuclear metal centres on catalytic activity has not been well recognized and revealed. Herein, we report a dinuclear cobalt complex featuring a planar structure, which displays outstanding catalytic efficiency for photochemical CO2-to-CO conversion. The turnover number (TON) and turnover frequency (TOF) values reach as high as 14457 and 0.40 s-1 respectively, 8.6 times higher than those of the corresponding mononuclear cobalt complex. Control experiments and theoretical calculations revealed that the enhanced catalytic efficiency of the dinuclear cobalt complex is due to the indirect DMSC effect between two CoII ions, energetically feasible one step two-electron transfer process by Co2 I,I intermediate to afford Co2 II,II(CO2 2-) intermediate and fast mass transfer closely related with the planar structure.

A Planar‐Structured Dinuclear Cobalt(II) Complex with Indirect Synergy for Photocatalytic CO2‐to‐CO Conversion

Dinuclear metal synergistic catalysis (DMSC) has been proved an effective approach to enhance catalytic efficiency in photocatalytic CO2 reduction reaction, while it remains challenge to design dinuclear metal complexes that can show DMSC effect. The main reason is that the influence of the microenvironment around dinuclear metal centres on catalytic activity has not been well recognized and revealed. Herein, we report a dinuclear cobalt complex featuring a planar structure, which displays outstanding catalytic efficiency for photochemical CO2‐to‐CO conversion. The turnover number (TON) and turnover frequency (TOF) values reach as high as 14457 and 0.40 s‐1 respectively, 8.6 times higher than those of the corresponding mononuclear cobalt complex. Control experiments and DFT calculations revealed that the enhanced catalytic efficiency of the dinuclear cobalt complex is due to the indirect DMSC effect between two CoII ions, energetically feasible one step two‐electron transfer process by Co2I,I intermediate to afford Co2II,II(CO22‐) intermediate and fast mass transfer closely related with the planar structure.

Unveiling the role of proton concentration in dinuclear metal complexes for boosting photocatalytic CO2 reduction

The reaction kinetics of photocatalytic CO2 reduction is highly dependent on the transfer rate of electrons and protons to the CO2 molecules adsorbed on catalytic centers. Studies on uncovering the proton effect in catalysts on photocatalytic activity of CO2 reduction are significant but rarely reported. In this paper, we, from the molecular level, revealed that the photocatalytic activity of CO2 reduction is closely related to the proton availability in catalysts. Specifically, four dinuclear Co(II) complexes based on Robson-type ligands with different number of carboxylic groups (-nCOOH; n = 0, 2, 4, 6) were designed and synthesized. All these complexes show photocatalytic activity for CO2 reduction to CO in a water-containing system upon visible-light illumination. Interestingly, the CO yields increase positively with the increase of the carboxylic-group number in dinuclear Co(II) complexes. The one containing -6COOH shows the best photocatalytic activity for CO2 reduction to CO, with the TON value reaching as high as 10,294. The value is 1.8, 3.4, and 7.8 times higher than those containing -4COOH, -2COOH, and -0COOH, respectively. The high TON value also makes the dinuclear Co(II) complex with -6COOH outstanding among reported homogeneous molecular catalysts for photocatalytic CO2 reduction. Control experiments and density functional theory calculation indicated that more carboxylic groups in the catalyst endow the catalyst with more proton relays, thus accelerating the proton transfer and boosting the photocatalytic CO2 reduction. This study, at a molecular level, elucidates that more carboxylic groups in catalysts are beneficial for boosting the reaction kinetics of photocatalytic CO2 reduction.

The performance and efficiency of twelve range-separated hybrid DFT functionals for calculation of the magnetic exchange coupling constants of di-nuclear first row transition metal complexes

The performance and efficiency of twelve range-separated hybrid functionals are compared with each other in calculating magnetic exchange coupling constant (J) data on eleven di-nuclear first-row transition metal complexes having di-copper (Cu) and di-vanadium (V) as their central atoms. The J values are then compared with the experimental findings. In addition to that we also computed the B3LYP results of these complexes. We compared them with the results obtained from range-separated functionals as well as with the experimental results to understand their performances in predicting the magnetic exchange coupling constant. When computing, we reoptimized all the structures of the complexes taken from the crystal data, and then the values of Js were determined. The performances are predicted in terms of four statistical error matrices, namely, the mean absolute error (MAE), mean fractional error (MFE), mean signed error (MSE), root mean square error (RMSE) in cm−1.

The Research work of Dr. Ishida ‐ including Syntheses and Their Photocatalytic CO2 Reduction of Dinuclear Metal Complexes with Peptide Linkages project

The process of photosynthesis holds potential to be harnessed for addressing increasing CO2 levels, as well as for finding solutions for energy shortages resulting from depleted fossil fuel reserves. Professor Hitoshi Ishida, Laboratory on Functional Metal Complexes, Kansai University, has extensive expertise in creating artificial enzymes and is interested in developing techniques to emulate photosynthesis. The plan is to create a new photocatalyst by combining photochemical CO2 reduction catalytic reactions for artificial photosynthesis with the technology of functional molecule design using ‘peptide origami’, whereby proteins fold to form higher-order structures and exhibit functions. Ishida and his team are seeking to achieve artificial photosynthesis by using ruthenium complexes as catalysts in CO2 reduction reactions that can reduce CO2 to carbon monoxide (CO) and formic acid (HCOOH), which are useful as energy sources. Ishida has created functional molecules combining metal complexes with proteins, including artificial metalloproteins ‐ a type of protein containing a metal ion ‐ using synthetic bipyridyl amino acid 5Bpy. This focused on a rare transition metal called ruthenium as the ruthenium complexes the researchers are investigating have a selectivity for carbon monoxide and formic acid reduction products that change depending on the reaction conditions. The ultimate goal of Ishida’s work is to find a solution to the problem of pollution, while addressing the need for alternatives to fossil fuels.

Metal- and ligand-substitution-induced changes in the kinetics and thermodynamics of hydrogen activation and hydricity in a dinuclear metal complex.

Catalytic function in organometallic complexes is achieved by carefully selecting their central metals and ligands. In this study, the effects of a metal and a ligand on the kinetics and thermodynamics of hydrogen activation, hydricity degree of the hydride complex, and susceptibility to electronic oxidation in bioinspired NiFe complexes, [NiIIX FeII(Cl)(CO)Y]+ ([NiFe(Cl)(CO)]+; X = N,N'-diethyl-3,7-diazanonane-1,9-dithiolato and Y = 1,2-bis(diphenylphosphino)ethane), were investigated. The density functional theory calculations revealed that the following order thermodynamically favored hydrogen activation: [NiFe(CO)]2+ > [NiRu(CO)]2+ > [NiFe(CNMe)]2+ ∼ [PdRu(CO)]2+ ∼ [PdFe(CO)]2+ ≫ [NiFe(NCS)]+. Moreover, the reverse order thermodynamically favored the hydricity degree.

Helical dinuclear 3d metal complexes with bis(bidentate) [S,N] ligands: synthesis, structural and computational studies.

A diprotic bis(β-thioketoimine) ligand precursor featuring a flexible 4,4'-methylbis(aniline) linker, H22, was synthesised via treatment of the corresponding bis(β-ketoimine) with Lawesson's reagent. Lithiation of H22 and coordination with one equivalent of d-block metal(II) chlorides MCl2(THF)x (M = Fe, Co and Zn) yielded a corresponding series of homoleptic dinuclear complexes, [M2(μ-2)2]. X-ray diffraction analysis reveals a tetrahedral geometry for the two metals and a double-stranded helicate structure arising from inter-strand face-face π-stacking. These interactions create a helical 'twist' of ca. 70°. Utilising a bulky mononucleating β-thioketoiminate ligand, [3]-, the analogous series of homoleptic monometallic complexes, [M(3)2] (M = Fe, Co and Zn), were prepared and characterised by spectroscopic and analytical techniques. A comprehensive DFT study of all complexes reveals a stronger M-S bonding compared to M-N due to a higher degree of covalency. Solution magnetic studies and natural bonding orbital calculations on the mono- and dinuclear iron and cobalt complexes are consistent with high-spin tetrahedral Fe(II) and Co(II) centres, and cyclic voltammetry reveals both oxidation and reduction processes are accessible.

Coordination Chemistry of Open-Ring Hemiporphyrazines

Hemiporphyrazines, phthalocyanine analogues consisting of two isoindoline subunits and two pyridine or other aromatic subunits, have attracted considerable interest not only from the viewpoint of their fundamental properties but also in materials science. Since the first report on hemiporphyrazine about 70 years ago, various types of hemiporphyrazines have been synthesized to date. However, when comparing the rich chemistry of porphyrins and other porphyrinoids, the structural diversity of hemiporphyrazines and azaporphyrinoids is still limited. In particular, much less attention has been paid for acyclic hemiporphyrazines, which is in sharp contrast to many reports on acyclic porphyrinoids. Herein we report synthesis of open-ring hemiporphyrazines and their coordination chemistry. Helical metal complexes (1M ) and dinuclear metal complexes ((2M)2 ) were obtained depending on the terminal subunit of the open-hemiporphyrazine ligands. The effects of the central metal ion on molecular and electronic structures will be discussed in the presentation. Figure 1

Reactivity of Rare-Earth Oxides in Anhydrous Imidazolium Acetate Ionic Liquids

Rare-earth metal sesquioxides (RE2O3) are stable compounds that require high activation energies in solid-state reactions or strong acids for dissolution in aqueous media. Alternatively, dissolution and downstream chemistry of RE2O3 have been achieved with ionic liquids (ILs), but typically with additional water. In contrast, the anhydrous IL 1-butyl-3-methylimidazolium acetate [BMIm][OAc] dissolves RE2O3 for RE = La–Ho and forms homoleptic dinuclear metal complexes that crystallize as [BMIm]2[RE2(OAc)8] salts. Chloride ions promote the dissolution without being included in the compounds. Since the lattice energy of RE2O3 increases with decreasing size of the RE3+ cation, Ho2O3 dissolves very slowly, while the sesquioxides with even smaller cations appear to be inert under the applied conditions. The Sm and Eu complex salts show blue and red photoluminescence and Van Vleck paramagnetism. The proton source for the dissolution is the imidazolium cation. Abstraction of the acidic proton at the C2-atom yields an N-heterocyclic carbene (imidazole-2-ylidene). The IL can be regenerated by subsequent reaction with acetic acid. In the overall process, RE2O3 is dissolved by anhydrous acetic acid, a reaction that does not proceed directly.

Quantum Stirling engine based on dinuclear metal complexes

Low-dimensional metal complexes are versatile materials with tunable physical and chemical properties that make these systems promising platforms for caloric applications. In this context, this work proposes a quantum Stirling cycle based on a dinuclear metal complex as a working substance. The results show that the quantum cycle operational modes can be managed when considering the change in the magnetic coupling of the material and the temperature of the reservoirs. Moreover, magnetic susceptibility can be used to characterize the heat exchanges of each cycle step and, therefore, its performance. As a proof of concept, the efficiency of the heat engine is obtained from experimental susceptibility data. These results open doors for studying quantum thermodynamic cycles by using metal complexes; and further the development of emerging quantum technologies based on these advanced materials.

Observation of protonation-induced intra-molecular metal-to-metal charge transfer in cyano-bridged [Fe-CN-Mn/Ni] dinuclear complexes.

A key challenge in the design of magnetic molecules with intramolecular charge transfer behavior is to obtain reversible magnetic bistability triggered by external stimuli. Here, we show that two dinuclear metal complexes, [(bbp)Fe(CN)3Mn(Py5Me2)]·2.5CH3OH (4) and [(bbp)Fe(CN)3Ni(Py5Me2)]·2.5CH3OH (5) (Py5Me2 = 2,6-bis(1,1-di(pyridine-2-yl)ethyl)pyridine, H2bbp = 2,6-bis(benzimidazole-2-yl)pyridine), were self-assembly synthesized by (Bu4N)2[(bbp)FeIII(CN)3] and [Mn(Py5Me2)(OH2)](ClO4)2 or [Ni(Py5Me2)(OH2)](ClO4)2, respectively. Complexes 4 and 5 exhibited intramolecular metal-to-metal charge transfer with the addition of acids or bases in solution by UV-visible spectrophotometric measurements and electrochemistry studies, and concomitant switching of the {FeIII(μ-CN)MnII/NiII} state to the {FeII(μ-CN)MnIII/NiIII} state.

A metal-organic framework-supported dinuclear iron catalyst for hydroboration of carbonyl compounds.

Preparation of catalytically active dinuclear transition metal complexes with an open coordination sphere is a challenging task because the metal sites tend to be "saturated" with excess donor atoms around during synthesis. By isolating the binding scaffolds with the metal-organic framework (MOF) skeleton and installing metal sites through post-synthetic modification, we succeed in constructing a MOF-supported metal catalyst, namely FICN-7-Fe2, with dinuclear Fe2 sites. FICN-7-Fe2 effectively catalyses the hydroboration of a broad range of ketone, aldehyde, and imine substrates with a low loading of 0.05 mol%. Remarkably, kinetic measurements showed that FICN-7-Fe2 is 15 times more active than its mononuclear counterpart FICN-7-Fe1, indicating that cooperative substrate activation on the two Fe centres significantly enhances the catalysis.

Highly Charged Ru(II) Polypyridyl Complexes as Photosensitizer Agents in Photodynamic Therapy of Epithelial Ovarian Cancer Cells.

Ovarian cancer recurrence is frequent and associated with chemoresistance, leading to extremely poor prognosis. Herein, we explored the potential anti-cancer effect of a series of highly charged Ru(II)-polypyridyl complexes as photosensitizers in photodynamic therapy (PDT), which were able to efficiently sensitize the formation of singlet oxygen upon irradiation (Ru12+ and Ru22+) and to produce reactive oxygen species (ROS) in their corresponding dinuclear metal complexes with the Fenton active Cu(II) ion/s ([CuRu1]4+ and [Cu2Ru2]6+). Their cytotoxic and anti-tumor effects were evaluated on human ovarian cancer A2780 cells both in the absence or presence of photoirradiation, respectively. All the compounds tested were well tolerated under dark conditions, whereas they switched to exert anti-tumor activity following photoirradiation. The specific effect was mediated by the onset of programed cell death, but only in the case of Ru12+ and Ru22+ was preceded by the loss of mitochondrial membrane potential soon after photoactivation and ROS production, thus supporting the occurrence of apoptosis via type II photochemical reactions. Thus, Ru(II)-polypyridyl-based photosensitizers represent challenging tools to be further investigated in the identification of new therapeutic approaches to overcome the innate chemoresistance to platinum derivatives of some ovarian epithelial cancers and to find innovative drugs for recurrent ovarian cancer.

Asymmetric Hydrophosphonylation of α,β-Unsaturated Ketones Catalyzed by Rare-Earth Metal Complexes Bearing Trost Ligands.

Chiral dinuclear rare-earth metal complexes RE2Ln2 (n = 1, RE = Y(1), Eu(2), Nd(3), La(4), Gd(5); n = 2, RE = Eu(6), Gd(7)) stabilized by the corresponding Trost ligands H3L1 or H3L2 (H3L1 = (S,S)-2,6-bis[2-(hydroxydiphenylmethyl)pyrrolidin-1-ylmethyl]-4-methylphenol, H3L2 = (S,S)-2,6-bis[2-(hydroxydiphenylmethyl)pyrrolidin-1-ylmethyl]-4-chlorophenol) were prepared and three unknown complexes 5-7 were characterized by X-ray diffraction analysis. The chiral rare-earth metal complexes 1-7 displayed high reactivity in the asymmetric hydrophosphonylation of α,β-unsaturated ketones, and 5 mol % of complex 7 together with 10 mol % of chiral diamine (1S,2S)-1,2-cyclohexanediamine were proved to be the optimal catalyst combination. Various hydrophosphonylation products with excellent yields and high to excellent enantiomeric excess (ee) values were obtained in toluene (up to 99% yield, >99% ee).

Electronic structures, bonding aspects and spectroscopic parameters of homo/hetero valent bridged dinuclear transition metal complexes

Bridged dinuclear metal complexes have fascinated scientists worldwide, and remarkable success has been achieved to unravel the electronic structures, structure–function relationship, coordination environments, and fine mechanistic details of the enzymes owing to the repercussion of biomimetic studies carried out on dinuclear model systems. Molecular level study of these systems integrated with spectroscopic study helps in gaining deep insights about structural and electronic aspects of natural enzymatic systems. Considering the same, here first time we report DFT study on bridged non-heme metal complexes based on N-Et-HPTB ligand system containing homovalent (MIIMII); {[(MnII)2(O2CCH3)(N-Et-HPTB)]2+; Species I), [(FeII)2(O2CCH3)(N-Et-HPTB)]2+; Species II), [(CoII)2(O2CCH3)(N-Et-HPTB)]2+; Species III)} and heterovalent (MIIIMII): {[(MnIII)(MnII)(O2)(N-Et-HPTB)]2+; Species Ia) [(FeIII)(FeII)(O2)(N-Et-HPTB)]2+; Species IIa) and [(CoIII)(CoII)(O2)(N-Et-HPTB)]2+; Species IIIa)} dinuclear metal centres. Bridging oxygen bears a significant spin density which may prompt important chemical reactions involving activation of bonds like C-H/O-H/N-H etc. TD-DFT calculations for UV–Visible absorption have been carried out to further shed light on structural–functional and electronic structures of these dinuclear species. Studying these dinuclear species may be a good starting point for the study of active sites of the bimetallic centre of dinuclear enzymes and thus may serve as fascinating spectroscopic models. Further, FMO analysis, MEP mapping, and NBO calculations were employed to analyze bonding aspects predict theoretical reactivity behaviour and any kind of stabilizing interactions present in the reported species.

Heterospin frustration in a metal-fullerene-bonded semiconductive antiferromagnet

Lithium-ion-encapsulated fullerenes (Li+@C60) are 3D superatoms with rich oxidative states. Here we show a conductive and magnetically frustrated metal–fullerene-bonded framework {[Cu4(Li@C60)(L)(py)4](NTf2)(hexane)}n (1) (L = 1,2,4,5-tetrakis(methanesulfonamido)benzene, py = pyridine, NTf2− = bis(trifluoromethane)sulfonamide anion) prepared from redox-active dinuclear metal complex Cu2(L)(py)4 and lithium-ion-encapsulated fullerene salt (Li+@C60)(NTf2−). Electron donor Cu2(L)(py)2 bonds to acceptor Li+@C60 via eight Cu‒C bonds. Cu–C bond formation stems from spontaneous charge transfer (CT) between Cu2(L)(py)4 and (Li+@C60)(NTf2−) by removing the two-terminal py molecules, yielding triplet ground state [Cu2(L)(py)2]+(Li+@C60•−), evidenced by absorption and electron paramagnetic resonance (EPR) spectra, magnetic properties and quantum chemical calculations. Moreover, Li+@C60•− radicals (S = ½) and Cu2+ ions (S = ½) interact antiferromagnetically in triangular spin lattices in the absence of long-range magnetic ordering to 1.8 K. The low-temperature heat capacity indicated that compound 1 is a potential candidate for an S = ½ quantum spin liquid (QSL).

The ascidian Lissoclinum patella, the patellamides and copper

The ascidian species Lissoclinum patella is found, amongst other places, around Heron Island on the Great Barrier Reef, Australia. L. patella has a cyanobacterial symbiont, Prochloron didemni, known to produce various cyclic peptides, including quantities of the cyclic pseudo-octapeptides, the patellamides. Patellamides are of pharmaceutical interest and have attracted the curiosity of coordination chemists because they can form quite stable mono- and di-nuclear transition metal complexes, particularly with copper(ii). For some patellamide derivatives, the binding of two CuII centres is cooperative and solution equilibria involving metal-free peptides, mono- and di-nuclear copper(ii) complexes, and various functions of these complexes have been described. These studies were also driven by the observation that the ascidians possess copper concentrations in excess of that in the seawater around Heron Island, and accumulation factors of approximately 104 have repeatedly been reported. New data presented here, based on inductively coupled plasma atomic emission spectroscopy (ICP-OES) and ICP-mass spectromety (MS) measurements, indicate that the 104 factor is overestimated and a factor >500 and up to approximately 3000 is more realistic.