Heterometallic Clusters Research Articles

Pyrazine-bridged polymetallic copper-iridium clusters.

Single crystals of the mol-ecular compound, {Cu20Ir6Cl8(C21H24N2)6(C4H4N2)3]·3.18CH3OH or [({Cu10Ir3}Cl4(IMes)3(pyrazine))2(pyrazine)]·3.18CH3OH [where IMes is 1,3-bis-(2,4,6-trimethylphen-yl)imidazol-2-yl-idene], with a unique heterometallic cluster have been prepared and the structure revealed using single-crystal X-ray diffraction. The mol-ecule is centrosymmetric with two {Cu10Ir3} cores bridged by a pyrazine ligand. The polymetallic cluster contains three stabilizing N-heterocyclic carbenes, four Cl ligands, and a non-bridging pyrazine ligand. Notably, the Cu-Ir core is arranged in an unusual shape containing 13 vertices, 22 faces, and 32 sides. The atoms within the trideca-metallic cluster are arranged in four planes, with 2, 4, 4, 3 metals in each plane. Ir atoms are present in alternate planes with an Ir atom featuring in the peripheral bimetallic plane, and two Ir atoms featuring on opposite sides of the non-adjacent tetra-metallic plane. The crystal contains two disordered methanol solvent mol-ecules with an additional region of non-modelled electron density corrected for using the SQUEEZE routine in PLATON [Spek (2015 ▸). Acta Cryst. C71, 9-18]. The given chemical formula and other crystal data do not take into account the unmodelled methanol solvent mol-ecule(s).

Robust heterometallic {In2CdO}-Organic framework for efficiently catalyzing CO2 cycloaddition and Knoevenagel condensation

The catalytic performance of MOFs mainly comes from the coordination defects of their metal ions. However, developing promising MOF catalysts with a large number of small coordination molecules on metal ions remains a huge challenge. Herein, we report a highly robust heterometallic {In2CdO}-organic framework of {[In2Cd(CPPDP)(µ3 − OH)(H2O)5](NO3)2⋅2DMF⋅3H2O}n (NUC-103) with scarcely reported [In2Cd(OH)(O2CR)5(H2O)5] clusters (abbreviated as {In2CdO}) as secondary building units (SBUs), each of which contains five associated water molecules, implying that activated host framework can serve as strong Lewis acid. In NUC-103, three rows of {In2CdO} are shaped into hierarchical triangle-nanochannels of 17.42 × 17.98 Å2 and triangle-microchannels of 10.15 × 11.00 Å2 along c axis. On account of the following unique characteristics such as three kinds of active sites (Lewis acid sites of In3+ and Cd2+, Lewis base sites of free Npyridine atoms and electrophilic H-bond donors (HBD) of µ3 − OH moieties), large solvent-free channels, high thermal stability, and resistance to various solvents, NUC-103a is a promising catalytic platform. Catalytic experiments prove that NUC-103a is a significant heterogeneous catalyst for the cycloaddition of CO2 with epoxides with exclusive selectivity and high conversion. In addition, NUC-103a as a bifunctional catalyst displays the high catalytic performance on the Knoevenagel condensation reactions of aldehydes and malononitrile. Therefore, this work not only provides an indium(III) + cadmium(II)-based heterometallic cluster of {In2CdO}, but also provides a valuable insight into designing metal–organic catalytic materials with high defect coordination.

Synthesis Strategies and Structures of Molecular Heterometallic Oxo Clusters.

Multinuclear heterometallic oxo clusters, composed of two or more different metal cations bridged by oxo ligands, represent an important class of molecular complexes known for their unique magnetic, catalytic, and electrochemical properties resulting from cooperative interactions between the metal cations. If three or more types of metal cations can be arranged as designed, their chemical and physical properties can be precisely and flexibly controlled, potentially creating innovative materials. However, research on hetero-trimetallic and hetero-tetrametallic oxo clusters remains limited. This review presents an interdisciplinary search of multinuclear heterometallic oxo clusters, regardless of the type of ligand, to explain and classify their synthesis strategies and structures. By cataloging crystallographically characterized heterometallic oxo clusters using ligand-per-metal values and synthesis method notations, valuable insights have been gained into effective synthesis methods for the precise arrangement of metal cations. The advantages and disadvantages of one-pot synthesis methods and synthesis strategies for achieving precise structural control of heterometallic oxo clusters are discussed with an emphasis on the prediction of their final structures. The insights from this review are expected to drive the development of synthetic and analytical techniques for the precise synthesis of heterometallic complexes in a predictable way.

Chiral Star-Shaped [CoIII3LnIII] Clusters with Enantiopure Schiff Bases: Synthesis, Structure, and Magnetism.

Two enantiomeric pairs of new 3d-4f heterometallic clusters have been synthesized from two enantiomer Schiff base derivatives: (R/S)-2-[(2-hydroxy-1-phenylethylimino)methyl] phenol (R-/S-H2L). The formulae of the series clusters are Co3Ln(R-L)6 (Ln = Dy (1R), Gd (2R)), Co3Ln (S-L)6 (Ln = Dy (1S), Gd (2S)), whose crystal structures and magnetic properties have been characterized. Structural analysis indicated that the above clusters crystallize in the chiral P213 group space. The central lanthanide ion has a coordination geometry of D3 surrounded by three [CoIII(L)2]- anions using six aliphatic oxygen atoms of L2- featuring a star-shaped [CoIII3LnIII] configuration. Magnetic measurements showed the presence of slow magnetic relaxation with an effective energy barrier of 22.33 K in the DyIII derivatives under a zero-dc field. Furthermore, the circular dichroism (CD) spectra of 1R and 1S confirmed their enantiomeric nature.

Unraveling the Intertwining Factors Underlying the Assembly of High-Nuclearity Heterometallic Clusters.

Two closely related yet distinctly different cationic clusters, [Dy52Ni44(HEIDA)36(OH)138(OAc)24(H2O)30]10+ (1) and [Dy112Ni76(HEIDA)44(EIDA)24(IDA)4(OH)268(OAc)48(H2O)44]4+ (2) (HEIDA=N-(2-hydroxyethyl)iminodiacetate), each featuring a multi-shell core of Platonic and Archimedean polyhedra, were obtained. Depending on the specific conditions used for the co-hydrolysis of Dy3+ and Ni2+, the product can be crystallized out as one particular type of cluster or as a mixture of 1 and 2. How the reaction process was affected by the amount of hydrolysis-facilitating base and/or by the reaction temperature and duration was investigated. It has been found that a reaction at a high temperature and/or for an extended period favors the formation of the compact and thermodynamically more stable 1, while a brief reaction with a large amount of the base is good for the kinetic product 2. By tuning these intertwining conditions, the reaction can be regulated toward a particular product.

Construction of S-doped cellulose nanocrystals with edge sulfur vacancies to enhance the generation of 1O2 and promote peroxymonosulfate (PMS) activation

The strategy of constructing edge sulfur vacancies at cellulose surface interfaces has attracted widespread interest in fields such as electronics, photonics, optoelectronics, electrocatalysis, environmental remediation, and biosensing. In this study, NiCo2S4 (NCS) was modified onto cellulose sulfide nanocrystals (SCNC) with chiral helical structures. Utilizing high energy β Particle bombardment on the surface of photocatalysts induces the generation of edge S vacancies in SCNC, while promoting the formation of heterometallic single-atom clusters (Con, Nin) in NCS. The edge sulfur vacancies on the surface of SCNC exhibit high reactivity and adsorption capacity. The aggregation of Co and Ni at this position can transfer photo generated electrons to the edge sulfur vacancies, thereby protecting the edge sulfur vacancies and prolonging the carrier lifetime. Electrons enriched in edge S vacancies can activate the O–O bond of PMS, thereby achieving efficient degradation of ciprofloxacin (CIP). The degradation kinetics constant of Con-Nin/NCS/SCNC-Sv/PMS is 1.69 times higher than that of NCS/SCNC/PMS. In addition, electron paramagnetic resonance (EPR) shows that the sample produces a large amount of 1O2 during photocatalysis This article constructs a new approach for protecting edge S vacancies with heterogeneous single atom clusters, providing a new perspective for achieving efficient photocatalytic degradation of CIP.

Oxidative Addition of E-H (E=C, N) Bonds to Transient Uranium(II) Centers.

Two-electron oxidative addition is one of the most important elementary reactions for d-block transition metals but it is uncommon for f-block elements. Here, we report the first examples of intermolecular oxidative addition of E-H (E=C, N) bonds to uranium(II) centers. The transient U(II) species was formed in-situ by reducing a heterometallic cluster featuring U(IV)-Pd(0) bonds with potassium-graphite (KC8). Oxidative addition of C-H or N-H bonds to the U(II) centers was observed when this transient U(II) species was treated with benzene, carbazole or 1-adamantylamine, respectively. The U(II) centers could also react with tetracene, biphenylene or N2O, leading to the formation of arene reduced U(IV) products and uranyl(VI) species via two- or four-electron processes. This study demonstrates that the intermolecular two-electron oxidative addition reactions are viable for actinide elements.

Oxidative Addition of E−H (E=C, N) Bonds to Transient Uranium(II) Centers

AbstractTwo‐electron oxidative addition is one of the most important elementary reactions for d‐block transition metals but it is uncommon for f‐block elements. Here, we report the first examples of intermolecular oxidative addition of E−H (E=C, N) bonds to uranium(II) centers. The transient U(II) species was formed in‐situ by reducing a heterometallic cluster featuring U(IV)‐Pd(0) bonds with potassium‐graphite (KC8). Oxidative addition of C−H or N−H bonds to the U(II) centers was observed when this transient U(II) species was treated with benzene, carbazole or 1‐adamantylamine, respectively. The U(II) centers could also react with tetracene, biphenylene or N2O, leading to the formation of arene reduced U(IV) products and uranyl(VI) species via two‐ or four‐electron processes. This study demonstrates that the intermolecular two‐electron oxidative addition reactions are viable for actinide elements.

Three [Ln2Co2] cluster-based three-dimensional frameworks: Syntheses, structure, and magnetocaloric effect

The heterometallic 3d-4f clusters are being researched, for some time now, as being applicable to molecular magnetism. Especially, the Gd3+-containing multi-nuclear clusters attract wide study attention, on account of the significant magnetocaloric effect (MCE). Herein, three-dimensional (3D) 3d-4f heterometallic clusters are successfully gained via solvothermal conditions, formulated as {[Ln2Co2Na2(L)2(C2O4)2(H2O)4]·(H2O)2}n (abbreviated as Ln2Co2, Ln = Gd for 1; Ln = Tb for 2, and Ln = Dy for 3; L = ethylenediaminetetraacetic acid disodium salt). Structural analysis shows that Ln2Co2 clusters are mainly consistent of the [Ln2Co2Na2(L)2(C2O4)2(H2O)4] metal frames, which are the asymmetric building units. Interestingly, [Ln2Co2Na2(L)2(C2O4)2(H2O)4] metal frames can be constructed by one chain-shaped [Ln2(C2O4)2], one [Na2(H2O)2] dimer, and two [CoL(H2O)] units. Tree building units are connected to constitute 3D structure of Ln2Co2. In addition, the metal ions make Gd2Co2 exhibit the magnetic entropy change (-∆Sm = 31.17 J kg−1 K−1 at 2.0 K and 7.0 T) and ideal -∆Sm value at low-field condition (20.18 J kg−1 K−1 at 2.0 K and 2.0 T).

Synthesis and crystal structure of the cluster (Et4N)[(Tp*)MoFe3S3(μ3-NSiMe3)(N3)3

The title compound, tetraethylammonium triazidotri-μ3-sulfido-[μ3-(trimethylsilyl)azanediido][tris(3,5-dimethylpyrazol-1-yl)hydroborato]triiron(+2.33)molybdenum(IV), (C8H20N)[Fe3MoS3(C15H22BN6)(C3H9NSi)(N3)3] or (Et4N)[(Tp*)MoFe3S3(μ3-NSiMe3)(N3)3] [Tp* = tris(3,5-dimethylpyrazol-1-yl)hydroborate(1−)], crystallizes as needle-like black crystals in space group P\overline{1}. In this cluster, the Mo site is in a distorted octahedral coordination model, coordinating three N atoms on the Tp* ligand and three μ3-bridging S atoms in the core. The Fe sites are in a distorted tetrahedral coordination model, coordinating two μ3-bridging S atoms, one μ3-bridging N atom from Me3SiN2−, and another N atom on the terminal azide ligand. This type of heterometallic and heteroleptic single cubane cluster represents a typical example within the Mo–Fe–S cluster family, which may be a good reference for understanding the structure and function of the nitrogenase FeMo cofactor. The residual electron density of disordered solvent molecules in the void space could not be reasonably modeled, thus the SQUEEZE [Spek (2015). Acta Cryst. C71, 9–18] function was applied. The solvent contribution is not included in the reported molecular weight and density.

Electronic Delocalization and σ-Aromaticity in Heterometallic Cluster with Multiple Thorium-Palladium Bonds.

Research on metal-metal bonds involving f-block actinides, such as thorium, lags far behind the well-studied metal-metal bonds of d-block transition metals. The complexes with Th-TM bonds are extremely rare; all previously identified examples have only a single Th-TM bond with the Th center at an invariably +IV oxidation state. Herein, we report a series of Th2Pdn (n = 2, 3, and 6) clusters (complexes 3, 4, and 7) with multiple Th(III)-Pd bonds. Theoretical studies reveal that the Th2Pdn unit allows electronic delocalization and σ aromaticity, leading to unexpected closed-shell singlet structures for these Th(III) species. This electronic delocalization is evident in the highest occupied molecular orbital of Th(III) complexes and facilitates a 2e reduction of alkyne by complex 7, resulting in the formation of 8. Complexes 7 and 8 are distinctive in featuring a Th2Pd6 core with six and eight Th-Pd bonds, respectively, making them the largest known d-f heterometallic clusters exhibiting metal-metal bonding.

Magneto-optical Properties of Chiral Co2Ln and Co3Ln2 (Ln = Dy and Er) Clusters.

A series of chiral heterometallic Ln-Co clusters, denoted as Co2Ln and Co3Ln2 (Ln = Dy and Er), were synthesized by reacting the chiral chelating ligand (R/S)-2-(1-hydroxyethyl)pyridine (Hmpm), CoAc2·4H2O, and Ln(NO3)3·6H2O. Co2Ln and Co3Ln2 exhibit perfect mirror images in circular dichroism within the 320-700 nm range. Notably, the Co2Er and Co3Er2 clusters display pronounced magnetic circular dichroism (MCD) responses of the hypersensitive f-f transitions 4I15/2-4G11/2 at 375 nm and 4I15/2-2H11/2 at 520 nm of ErIII ions. This study highlights the strong magneto-optical activity associated with hypersensitive f-f transitions in chiral 3d-4f magnetic clusters.

Tuning Electrocatalytic Water Oxidation Activity: Insights from the Active-Site Distance in LnCu6 Clusters.

Atomically precise metal clusters serve as a unique model for unraveling the intricate mechanism of the catalytic reaction and exploring the complex relationship between structure and activity. Herein, three series of water-soluble heterometallic clusters LnCu6, abbreviated as LnCu6-AC (Ln = La, Nd, Gd, Er, Yb; HAC = acetic acid), LnCu6-IM (Ln = La and Nd; IM = Imidazole), and LnCu6-IDA (Ln = Nd; H2IDA = Iminodiacetic acid) are presented, each featuring a uniform metallic core stabilized by distinct protected ligands. Crystal structure analysis reveals a triangular prism topology formed by six Cu2+ ions around one Ln3+ ion in LnCu6, with variations in Cu···Cu distances attributed to different ligands. Electrocatalytic oxygen evolution reaction (OER) shows that these different LnCu6 clusters exhibit different OER activities with remarkable turnover frequency of 135s-1 for NdCu6-AC, 79s-1 for NdCu6-IM and 32s-1 for NdCu6-IDA. Structural analysis and Density Functional Theory (DFT) calculations underscore the correlation between shorter Cu···Cu distances and improves OER catalytic activity, emphasizing the pivotal role of active-site distance in regulating electrocatalytic OER activities. These results provide valuable insights into the OER mechanism and contribute to the design of efficient homogeneous OER electrocatalysts.

Study on magnetic properties of two dysprosium(III)-substituted antimonotungstates with different substitution modes

Two Polyoxometalates have been constructed by simple hydrothermal synthesis using rare-earth (RE) and antimonotungstates (ATs) {B-α-SbW9O33} as raw materials with the molecular formulas of H4.5Na1.5(H2O)6(C3H5N2)3{Na(Sb3O)2[B-β-SbW8O31Dy(H2O)2]3}·12H2O (1) and H9(C3H5N2)5{[Sb6IIISbVDy2WO10(H2O)5][(B-β-SbW9O33)2(B-α-SbW9O33)]}·16H2O (2). X-ray Single crystal diffractometer analysis shows that both 1 and 2 possess trimer configurations. Polyoxoanion 1 is assembled from three trilacunary {B-β-SbW8O31Dy(H2O)2}p units linked via {Na(Sb3O)2} cluster, where the trilacunary {B-β-SbW8O31Dy(H2O)2} unit is formed by the tetralacunary {B-β-SbW8O31} unit captures one Dy(H2O)23+ cation. Polyoxoanion 2 is composed of a novel 5p−4f heterometallic cluster {Sb6IIISbVDy2WO12(H2O)5} simultaneously stabilized by two {B-β-SbW9O33} units and one {B-α-SbW9O33} unit. In addition, two-dimensional correlation infrared spectroscopy (2D COS-IR) under magnetic disturbance was measured to investigate the difference of the variable temperature magnetic susceptibility between two compounds to explore the source of magnetic properties, and further magnetic property tests indicate that 1 and 2 may exhibit single-molecule-magnet behavior with distinct frequency dependence. This work deepens the theory of 2D COS-IR and also enriches the theoretical and experimental data of magnetism.

Development of Heterometallic Annular Tetranuclear Clusters in Metal–Organic Frameworks for Methane Purification and Storage

Development of Heterometallic Annular Tetranuclear Clusters in Metal–Organic Frameworks for Methane Purification and Storage

A topological analysis of the bonding interaction within the tri-nuclear heterometallic cluster [Mo–Ru–Co(µ3–S)(CO)8(Cp)COOCH3], (Cp = η5-C5H4)

A topological analysis of the bonding interaction within the tri-nuclear heterometallic cluster [Mo–Ru–Co(µ3–S)(CO)8(Cp)COOCH3], (Cp = η5-C5H4)

Interplay between protonation and Jahn-Teller effects in a manganese vanadium cubane water oxidation catalyst.

Understanding the protonation behavior of metal-oxo water oxidation catalysts is essential to improve catalyst efficiency and long-term performance, as well as to tune their properties for specific applications. In this work, we explore the basicity and protonation effects of the highly active water oxidation catalyst [(Mn4O4) (V4O13) (OAc)3]3- using density functional theory. We computed the relative free energies of protonation in a systematic fashion for all symmetry-inequivalent O atoms, where the presence of multiple oxidation states from Mn4IV to Mn4III and a rich Jahn-Teller isomerism adds a significant amount of complexity. For high oxidation states, the compound behaves like some other polyoxometalates, showing protonation preferably at the terminal and μ2-bridging O atoms of the vanadate cap. However, upon reduction, eventually, the protonation preference switches to the cubane O atoms, mostly driven by a strong increase in basicity for O atoms located along the Jahn-Teller axes. Our work further evidences that protonation can potentially lead to several chemical transformations, like disproportionation and charge transfer to vanadium, dissociation of ligands, or the opening of the cubane structure. Our simulated UV/Vis absorption spectra additionally provide valuable insights about how the protonation of the catalyst could be tracked experimentally. Overall, our analysis highlights the complexity involved in the protonation of heterometallic polyoxometalate clusters.

Three-Coordinate Nickel and Metal-Metal Interactions in a Heterometallic Iron-Sulfur Cluster.

Biological multielectron reactions often are performed by metalloenzymes with heterometallic sites, such as anaerobic carbon monoxide dehydrogenase (CODH), which has a nickel-iron-sulfide cubane with a possible three-coordinate nickel site. Here, we isolate the first synthetic iron-sulfur clusters having a nickel atom with only three donors, showing that this structural feature is feasible. These have a core with two tetrahedral irons, one octahedral tungsten, and a three-coordinate nickel connected by sulfide and thiolate bridges. Electron paramagnetic resonance (EPR), Mössbauer, and superconducting quantum interference device (SQUID) data are combined with density functional theory (DFT) computations to show how the electronic structure of the cluster arises from strong magnetic coupling between the Ni, Fe, and W sites. X-ray absorption spectroscopy, together with spectroscopically validated DFT analysis, suggests that the electronic structure can be described with a formal Ni1+ atom participating in a nonpolar Ni-W σ-bond. This metal-metal bond, which minimizes spin density at Ni1+, is conserved in two cluster oxidation states. Fe-W bonding is found in all clusters, in one case stabilizing a local non-Hund state at tungsten. Based on these results, we compare different M-M interactions and speculate that other heterometallic clusters, including metalloenzyme active sites, could likewise store redox equivalents and stabilize low-valent metal centers through metal-metal bonding.

Soluble Gd6Cu24 clusters: effective molecular electrocatalysts for water oxidation.

The water oxidation half reaction in water splitting for hydrogen production is extremely rate-limiting. This study reports the synthesis of two heterometallic clusters (Gd6Cu24-IM and Gd6Cu24-AC) for application as efficient water oxidation catalysts. Interestingly, the maximum turnover frequency of Gd6Cu24-IM in an NaAc solution of a weak acid (pH 6) was 319 s-1. The trimetallic catalytic site, H2O-GdIIICuII2-H2O, underwent two consecutive two-electron two-proton coupled transfer processes to form high-valent GdIII-O-O-CuIII2 intermediates. Furthermore, the O-O bond was formed via intramolecular interactions between the CuIII and GdIII centers. The results of this study revealed that synergistic catalytic water oxidation between polymetallic sites can be an effective strategy for regulating O-O bond formation.

Cluster dynamics of heterometallic trinuclear clusters during ligand substitution, redox chemistry, and group transfer processes.

Stepwise metalation of the hexadentate ligand tbsLH6 (tbsLH6 = 1,3,5-C6H9(NHC6H4-o-NHSiMe2tBu)3) affords bimetallic trinuclear clusters (tbsL)Fe2Zn(thf) and (tbsL)Fe2Zn(py). Reactivity studies were pursued to understand metal atom lability as the clusters undergo ligand substitution, redox chemistry, and group transfer processes. Chloride addition to (tbsL)Fe2Zn(thf) resulted in a mixture of species including both all-zinc and all-iron products. Addition of ArN3 (Ar = Ph, 3,5-(CF3)2C6H3) to (tbsL)Fe2Zn(py) yielded a mixture of two trinuclear products: (tbsL)Fe3(μ3-NAr) and (tbsL)Fe2Zn(μ3-NAr)(py). The two imido species were separated via crystallization, and outer sphere reduction of (tbsL)Fe2Zn(μ3-NAr)(py) resulted in the formation of a single product, [2,2,2-crypt(K)][(tbsL)Fe2Zn(μ3-NAr)]. These results provide insight into the relationship between heterometallic cluster structure and substitutional lability and could help inform both future catalyst design and our understanding of metal atom lability in bioinorganic systems.