Metal-metal Interactions Research Articles

Bimetallic Zn3Sn2 electrocatalyst derived from mixed oxides enhances formate production towards CO2 electroreduction reaction

As a potential approach to mitigate greenhouse effect meanwhile produce value-added chemical, electrochemical reduction reaction of CO2 (eCO2RR) to formate has gained increasing popularity recently, while its development is impeded by lack of electrocatalyst with satisfying selectivity and activity and low toxicity. Herein, we develop bimetallic Zn3Sn2 catalyst in-situ originated from the hetero-structured ZnxSnyOz nanoparticles supported on CNTs. With an optimized composition, the Zn3Sn2 catalyst (YSn = 39.1 %) achieves higher selectivity for formate by suppressing CO adsorption and reducing the energy barrier of formate intermediate *OCHO compared to its pristine counterparts, which is supported by DFT calculation. It enables a remarkably high Faradic efficiency (FE)formate of 96.7 %, formate yield (924 ppm h−1 mg−1), 26.0 mA cm−2 partial current density of formate (jformate), and better durability in flow cell at −1.1 V vs. reversible hydrogen electrode (RHE), which outperforms most of the reported electrocatalysts for CO2-to-formate conversion. The enhanced formate production from eCO2RR is unlocked for the synergistic effect between Zn-Sn system, implicating vast possibility to improve the electrocatalytic reactivity utilizing metal-metal interaction.

Metal-Metal Oxide Catalytic Interface Formation and Structural Evolution: A Discovery of Strong Metal-Support Bonding, Ordered Intermetallics, and Single Atoms.

In-depth investigation of metal-metal oxide interactions and their corresponding evolution is of paramount importance to heterogeneous catalysis as it allows the understanding and maneuvering of the structure of catalytic motifs. Herein, using a series of core/shell metal/iron oxide (M/FeOx, M = Pd, Pt, Au) nanoparticles and through a combination of in situ and ex situ electron and X-ray investigations, we revealed anomalous and dissimilar M-FeOx interactions among different systems under reducing conditions. Pd interacts strongly with FeOx after high-temperature reductive treatment, featured by the formation of Pd single atoms in the FeOx matrix and increased Pd-Fe bonding, while Pt transforms into ordered PtFe intermetallics and Pt single atoms immediately upon the coating of FeOx. In contrast, Au does not manifest strong bonding with FeOx. As a proof of concept of tailoring metal-metal oxide interactions for catalysis, optimized Pd/FeOx demonstrates 100% conversion and 86.5% selectivity at 60 °C for acetylene semihydrogenation.

Efficient electrocatalysts with strong core-shell interaction for water splitting: The modulation of selectivity and activity

Optimum of electrocatalysts plays a key role in the design and development of cost-effective and environmentally benign technologies for energy conversion and storage. In this work, we study two kinds of core-shell structured electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acid and alkali electrolyte. The electrocatalyst of cobalt@cobalt phosphide nanoparticles is grown on carbon nanotubes (Co@CoP/CNT) and shows a current density of 10 mA cm−2 at an overpotential of 67 mV in acid and 125 mV in alkali, demonstrating the strong metal-metal phosphide interaction facilitating hydrogen reduction. However, the in situ formed cobalt@cobalt oxide (Co@Co3O4/CNT) electrocatalysts from the Co@CoP/CNT can retard both the HER and OER performances through the metal-metal oxide interaction. The underlying mechanisms of the activity and selectivity of the core-shell catalysts towards water splitting reactions is further unveiled by density functional theory (DFT) simulation. The different catalytic behaviors of the core-shell structured catalysts in HER and OER are attributed to the different interactions between the metallic cores, shells and the adsorbed intermediate species. This study not only promises a facile and general strategy to fabricate high performance electrocatalysts but also sheds new light on crucial design principles of catalyst materials for intermediate-selective electrocatalytic reactions.

Synthesis of Square Planar Cu4 Clusters.

Template-assisted synthesis of well-defined polynuclear clusters remains a challenge for [M4 ] square planar topologies. Herein, we present a tetraamine scaffold R L(NH2 )4 , where L is a rigidified resorcin[4]arene, to direct the formation of C4 -symmetric R L(NH)4 Cu4 clusters with Cu-Cu distances around 2.7 Å, suggesting metal-metal direct interactions are operative since the sum of copper's van der Waals radii is 2.8 Å. DFT calculations display HOMO to HOMO-3 residing all within a 0.1 eV gap. These four orbitals display significant electron density contribution from the Cu centers suggesting a delocalized electronic structure. The one-electron oxidized [Cu4 ]+ species was probed by variable temperature X-band continuous wave-electron paramagnetic resonance (CW-EPR), which displays a multiline spectrum at room temperature. This work presents a novel synthetic strategy for [M4 ] clusters and a new platform to investigate activation of small molecules.

Green synthesis approach for preparing zeolite based Co-Cu bimetallic catalysts for low temperature CO2 hydrogenation to methanol

In this study, zeolite based Cu-Co bimetallic catalysts were synthesized by green deposition precipitation method. To investigate the optimum metal-metal ratio, catalysts with different Cu-Co metal weight ratios were evaluated for CO2 hydrogenation to methanol. The XRD analysis revealed crystalline nature of zeolite support with deposition of highly dispersed Cu-Co metal oxides. The FESEM observation showed well dispersed morphology of zeolite based Cu-Co bimetallic catalysts. The nitrogen adsorption-desorption studies showed that surface area of Cu-Co bimetallic catalysts was slightly decreased by increasing Cu content in bimetallic catalysts. Temperature program reduction studies exhibited synergism between the Cu-Co metals which resulted variation in reduction behavior of zeolite based Cu-Co bimetallic catalysts. Similarly, XPS studies revealed metal-metal interaction by shifting XPS peaks to higher binding energies regions. Temperature program desorption investigations showed the existence of three types of basic sites on the surface of zeolite based Cu-Co bimetallic catalysts. Activity profiles of zeolite based Cu-Co bimetallic catalysts were examined for low temperature CO2 hydrogenation to methanol in slurry reactor. The activity studies documented enhancement in methanol synthesis rate from 7.5 to 25.6 g/Kgcat.h by increasing the Cu content in catalysts. Based on the physico-chemicals findings and activity data, structure-activity patterns were elaborated in details.

Tuning crystal-phase of bimetallic single-nanoparticle for catalytic hydrogenation

Bimetallic nanoparticles afford geometric variation and electron redistribution via strong metal-metal interactions that substantially promote the activity and selectivity in catalysis. Quantitatively describing the atomic configuration of the catalytically active sites, however, is experimentally challenged by the averaging ensemble effect that is caused by the interplay between particle size and crystal-phase at elevated temperatures and under reactive gases. Here, we report that the intrinsic activity of the body-centered cubic PdCu nanoparticle, for acetylene hydrogenation, is one order of magnitude greater than that of the face-centered cubic one. This finding is based on precisely identifying the atomic structures of the active sites over the same-sized but crystal-phase-varied single-particles. The densely-populated Pd-Cu bond on the chemically ordered nanoparticle possesses isolated Pd site with a lower coordination number and a high-lying valence d-band center, and thus greatly expedites the dissociation of H2 over Pd atom and efficiently accommodates the activated H atoms on the particle top/subsurfaces.

Design of macrostructured bimetallic MWCNT catalysts for multi-phasic hydrogenation in water treatment with pre- and post-coating metal phase impregnation

The development of macrostructured catalysts for remediation processes is a key step towards the sustainability of multi-phase environmental systems, such as the catalytic reduction of inorganic contaminants. The advances towards practical applications faces great challenges regarding the availability of active centers on catalysts surface. To improve the catalytic activity of macrostructured bimetallic catalysts, it is crucial to understand which are the properties that most influence the catalytic activity of materials deposited on macrostructured supports. This work presents a systematic study on the design of macrostructured bimetallic catalysts with enhanced catalytic activity and selectivity. These materials were tested for selective NO3- conversion to N2. The adoption of different synthesis methodologies allowed a higher metal-metal interaction, which is an important property influencing the efficiency of the bimetallic catalyst. Metal phase distribution through coating layers proved to be a key-step for the synthesis of more active and N2 selective structured catalysts.

Carrier-induced metal-insulator transition in trirutile MgTa2O6

Materials exhibiting metal-insulator transitions (MITs) are proposed platforms for next-generation low-power electronics. Many of these materials exhibit strong coupling between the electronic and lattice degrees of freedom, which makes them ideal systems to examine the interplay between lattice dynamics, electronic structure, and magnetic order. The rutile structure, featuring edge-connected octahedral chains along its $c$ axis, permits metal-metal interactions that can induce metal-insulator transitions. Although the MITs in rutile-structured compounds have been thoroughly studied, the derivative trirutile phase, which accommodates similar metal-metal interactions, has yet to be examined in the context of MITs. Here we use density functional theory calculations to investigate a carrier-driven MIT in trirutile ${\mathrm{MgTa}}_{2}{\mathrm{O}}_{6}$, a ${d}^{0}$ insulator with a suitable axial ratio. Our calculations suggest the existence of four distinct phases in ${\mathrm{MgTa}}_{2}{\mathrm{O}}_{6}$ with increasing electron concentration: nonmagnetic insulator, ferromagnetic (FM) metal, FM half-metal, and nonmagnetic insulator. We explain how the resulting electronic phases arise from changes in atomic structure with increasing carrier density. Our results indicate that trirutile oxides may be a promising materials class for which to access and functionalize MITs.

(Invited) Actinide-Metal Interactions in Endohedral Fullerenes: An-an@C2n and an-M@C2n

The existence of actinide-actinide (An-An) bonding interactions has been a controversial and actively researched topic in inorganic chemistry for many years. Calculations for An-An interactions inside fullerene cages (endohedral fullerenes) typically conclude that the weak interactions observed are the result of compression due to the presence of the carbon cage but these results and interpretations fail to address the mechanistic implications of the conclusions because they don't address the reasons why two An atoms would find themselves trapped inside a cage if they don't really like to interact with each other. How can we understand the prevalence of so many An-An@C2n as well as An-M@C2n endohedral compounds, some of which are obtained in very reasonable quantities, if there is no real driving force for their simultaneous incorporation inside the carbon cages. In this work we will present experimental and theoretical results that together show that there are reasonable metal-metal interactions inside these endohedral structures.

Boosting the deep oxidation of propane over zeolite encapsulated Rh-Mn bimetallic nanoclusters: Elucidating the role of confinement and synergy effects

Metal nanocluster catalysts with superior activity and stability are urgently needed in the deep oxidation of volatile organic compounds (VOCs). In this study, a novel silicalite-1 zeolite confined rhodium-manganese bimetallic nano-cluster (1.6 nm) catalyst (Rh-MnOx@S-1) was designed and prepared by a simple one-pot method using a dual confinement strategy (shell confinement and strong metal-metal oxide interaction) and applied in the deep oxidation of propane. The results revealed that the temperature at 90% conversion (T90) for propane over Rh-MnOx@S-1 was as low as 264 °C, which is evidently higher than the conventional supported (Rh-MnOx/S-1, T90 = 369 °C) and the MnOx-free (Rh@S-1, T90 = 285 °C) catalysts. Moreover, the turnover frequency (TOF) value of Rh-MnOx@S-1 at 220 °C was up to 16 × 10−3 s−1, which is approximately 5–6 times higher than those of comparable catalysts. Most importantly, Rh-MnOx@S-1 also exhibited excellent high temperature thermal stability, water resistance and recyclability, which can be attributed to the confinement effect of the zeolite shell and the synergistic electronic-structure interaction between the Rh and MnOx species. The in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) analysis indicates that the C3H8 deep oxidation mechanism over Rh-MnOx@S-1 catalyst follows the Mars-van Krevelen (MvK) mechanism, i.e., the adsorbed C3H8 species reacted with the activated oxygen species from Rh-MnOx interfaces. The dual confinement strategy developed in this study provides a new way to design high performance catalysts for the removal of VOCs under harsh reaction conditions.

Model Compounds for Intermediates and Transition States in Sonogashira and Negishi Coupling:d8–d10Bonds in Large Heterobimetallic Complexes Are Weaker than Computational Chemistry Predicts

We report an experimental study, with accompanying DFT calculations, on a series of heterobimetallic complexes with Pd(II) and Cu(I), Ag(I), or Au(I). The isolable pincer complexes are models for the intermediates and transition state for the transmetalation step in Sonogashira and Negishi coupling reactions, among which, according to the DFT calculations, only the transition state has the two metal centers within bonding distance. Furthermore, we report a substituted version of an analogous heterobimetallic complex in which a competing dissociation sets an upper-bound on the strength of the d8-d10 metal-metal bond. Analysis of the structures in the solid state and in solution, and the competitive dissociation experiment in the gas phase, indicate that the dispersion-corrected DFT method used in the study appears to overestimate the strength of the metal-metal interaction, thus distorting the shape of the computed potential energy surface systematically for transmetalation.

Which Is Better for Hydrogen Evolution on Metal@MoS2 Heterostructures from a Theoretical Perspective: Single Atom or Monolayer?

Single atom (SA)- and monolayer (ML)-supported catalysts are two main technical routines to increase electrochemical catalytic performance and reduce cost. To date, it is still a debate which one is better for catalysis in experiments as both routines face a puzzling problem of searching for balance between stability and catalytic activity. Here, hydrogen evolution on two-dimensional 2H-MoS2 with SA- and ML-adsorbed metal atoms (23 kinds in total) is taken as an example to solve this question by first-principles calculations. The thermodynamic stability during synthesis, in vacuum, and in electrochemical reaction conditions is determined to access the stability of MoS2 loaded with single (MS@MoS2) and monolayer metal atoms (MM@MoS2). The realistic catalytic surfaces determined by surface Pourbaix diagrams, the free energy changes of hydrogen atoms at different coverages, and the exchange current densities are applied to determine hydrogen evolution reaction (HER) activity. The results show that all MM@MoS2 are much more stable than the corresponding MS@MoS2 as the metal-metal interaction in MLs could make the former structures more stable. In general, MM@MoS2 show higher hydrogen evolution activities than those of MS@MoS2. In detail, the exchange current densities of MoS2 loaded by Pd ML and Au ML are 6.208, and 1.109 mA/cm-2, respectively, which are comparable to Pt(111). Combining with small binding energies, the Pd and Au MLs are the most promising catalysts for hydrogen evolution. The purpose of this work is to highlight the advantages and disadvantages of SA- and ML-supported surfaces as HER catalysts and provide a fundamental standard for studying them.

Supramolecular Hybrids from Cyanometallate Complexes and Diblock Copolypeptide Amphiphiles in Water.

The self-assembly of discrete cyanometallates has attracted significant interest due to the potential of these materials to undergo soft metallophilic interactions as well as their optical properties. Diblock copolypeptide amphiphiles have also been investigated concerning their capacity for self-assembly into morphologies such as nanostructures. The present work combined these two concepts by examining supramolecular hybrids comprising cyanometallates with diblock copolypeptide amphiphiles in aqueous solutions. Discrete cyanometallates such as [Au(CN)2]−, [Ag(CN)2]−, and [Pt(CN)4]2− dispersed at the molecular level in water cannot interact with each other at low concentrations. However, the results of this work demonstrate that the addition of diblock copolypeptide amphiphiles such as poly-(L-lysine)-block-(L-cysteine) (Lysm-b-Cysn) to solutions of these complexes induces the supramolecular assembly of the discrete cyanometallates, resulting in photoluminescence originating from multinuclear complexes with metal-metal interactions. Electron microscopy images confirmed the formation of nanostructures of several hundred nanometers in size that grew to form advanced nanoarchitectures, including those resembling the original nanostructures. This concept of combining diblock copolypeptide amphiphiles with discrete cyanometallates allows the design of flexible and functional supramolecular hybrid systems in water.

TM3 (TM = V, Fe, Mo, W) single-cluster catalyst confined on porous BN for electrocatalytic nitrogen reduction

• Confined metal clusters in the triplet form as sub-nanometer reactors for NRR. • Mo 3 @p-BN exhibits excellent catalytic activity and selectivity. • A rather low limiting potential (−0.34 V) was obtained. • Mo atoms act as “cache” to accelerate electron transfer. • Synergistic effect makes the “donation–backdonation” mechanism more efficient. Confined metal clusters as sub-nanometer reactors for electrocatalytic N 2 reduction reaction (eNRR) have received increasing attention due to the unique metal-metal interaction and higher activity than single-atom catalysts. Herein, the inspiration of the superior capacitance and unique microenvironment with regular surface cavities of the porous boron nitride (p-BN) nanosheets, we systematically studied the catalytic activity for NRR of transition-metal single-clusters in the triplet form (V 3 , Fe 3 , Mo 3 and W 3 ) confined in the surface cavities of the p-BN sheets by spin-polarized density functional theory (DFT) calculations. After a two-step screening strategy, Mo 3 @p-BN was found to have high catalytic activity and selectivity with a rather low limiting potential (–0.34 V) for the NRR. The anchored Mo 3 single-cluster can be stably embedded on the surface cavities of the substrate preventing the diffusion of the active Mo atoms. More importantly, the Mo atoms in the Mo 3 single-cluster would act as “cache” to accelerate electron transfer between active metal centers and nitrogen-containing intermediates via the intimate Mo-Mo interactions. The cooperation of Mo atoms can also provide a large number of occupied and unoccupied d orbitals to make the "donation–backdonation" mechanism more effective. This work not only provides a quite promising electrocatalyst for NRR, but also brings new insights into the rational design of triple-atom NRR catalysts.

Metal-metal interactions in correlated single-atom catalysts

Single-atom catalysts (SACs) include a promising family of electrocatalysts with unique geometric structures. Beyond conventional ones with fully isolated metal sites, an emerging class of catalysts with the adjacent metal single atoms exhibiting intersite metal-metal interactions appear in recent years and can be denoted as correlated SACs (C-SACs). This type of catalysts provides more opportunities to achieve substantial structural modification and performance enhancement toward a wider range of electrocatalytic applications. On the basis of a clear identification of metal-metal interactions, this review critically examines the recent research progress in C-SACs. It shows that the control of metal-metal interactions enables regulation of atomic structure, local coordination, and electronic properties of metal single atoms, which facilitate the modulation of electrocatalytic behavior of C-SACs. Last, we outline directions for future work in the design and development of C-SACs, which is indispensable for creating high-performing new SAC architectures.

Recent Advances in Carbon and Metal Based Supramolecular Technology for Supercapacitor Applications.

As the world moves towards renewable and sustainable energy sources, the need for systems that can quickly and safely store this energy is also rising. Supercapacitors (SCs) are among the most promising alternatives to conventional lithium-ion batteries. SCs are more stable, have higher-power densities, and can be charged much faster. However, SCs have their issues, and three of the main drawbacks of current SCs are 1) lower energy densities, 2) high cost of production, and 3) safety concerns in wearable devices. In this review, we discuss recent progress made in supramolecule-based SCs (SSCs). In supramolecular systems, molecules are held stable using non-covalent-type bonds. This allows for a flexible system in which the molecular interaction sites can easily break and reform at low energy, allowing for exposure of highly active sites and self-healing. When heterometal atoms are introduced into these supramolecular systems, this allows for further activation of the metal sites through the metal-metal interaction along with the metal-ligand interactions. This review discusses different types of SSCs (carbon-based and metal-incorporated) that have been utilized in recent years depending on their synthesis process. The working principle of SSCs and the utilization of different supramolecular elements that enhance the performance of SCs have also been discussed.

Hybrid Cu-Containing Compounds Based on Lacunary Strandberg Anions: Synthesis under Mild Conditions, Crystal Structure, and Magnetic Properties.

A one-pot reaction of a copper source (metallic powder Cu0 or Cu2+ salts) and bpy (bpy = 2,2'-bipyridine) in the presence of (NH4)2HPO4 and (NH4)6Mo7O24·4H2O yields heterometallic hybrid compounds of the general type {[Cu(bpy)n(H2O)m]p[P2MoxOy]}. The structures exhibit a number of phosphomolybdate POMs including not only a common Strandberg anion [P2Mo5O23]6- but also its unprecedented bi- and trilacunary derivatives [P2Mo3O18]8- and [P2Mo2O15]8-. The structural determinants including the metal source (copper powder vs copper salts), counterion of the salts, and stoichiometry of the reagents were examined. An ex situ EPR study revealed the formation of different CuII complexes in the reaction mixture depending on the copper precursor. The obtained compounds have been found to possess selectivity toward the sorption of methylene blue in a mixture of organic dyes. DC magnetic measurements of 1-3 indicate rather strong antiferromagnetic metal-metal exchange interactions. Compound 1 exhibits field-induced slow magnetic relaxation in AC magnetic measurements, which is a rarely observed phenomenon among Cu(II) complexes.

A Bis-(carbone) Pincer Ligand and Its Coordinative Behavior toward Multi-Metallic Configurations.

Carbones are divalent carbon(0) species that contain two lone pairs of electrons. Herein, we have prepared the first known stable and isolable free bis-(carbone) pincer framework with a well-defined solid-state structure. This bis-(carbone) ligand is an effective scaffold for forming monometallic (Ni and Pd) and trinuclear heterometallic complexes with Au-Pd-Au, Au-Ni-Au, and Cu-Ni-Cu configurations. Sophisticated quantum-theoretical analyses found that the metal-metal interactions are too weak to play a significant role in upholding these multi-metallic configurations; rather, the four lone pairs of electrons within the bis-(carbone) framework are the main contributors to the stability of the complexes.

Structural Control and Chiroptical Response in Intrinsically Tetra- and Pentanuclear Chiral Gold Clusters.

Controlling the synthesis of chiral metal clusters in the aspects of nuclearity number, metal-metal interaction, and spatial arrangement of metal atoms is crucial for establishing the correlation of detailed structural factors with chiroptical activity. Herein, a series of enantiopure gold complexes with nuclearity numbers ranging from 2 to 5 were constructed and structurally characterized. On the basis of the annulation reaction between two aurated μ2-imido nucleophilic units with various aldehydes, we finely adjusted the metal-metal interaction and torsion angles of a characteristic tetranuclear metal cluster by introducing different substituents into the resulting imidazolidine dianionic chiral skeleton. Further structural investigations, contrast experiments, and time-dependent density functional theory calculations confirmed that the chiroptical response of the acquired asymmetric metal clusters was mainly affected by the geometrically twisted arrangement of metal atoms. Finally, the tetranuclear gold cluster compound with the shortest intermetallic interaction and the largest torsion angle of a Au4 core showed the highest absorption anisotropy factor up to 2.2 × 10-3. In addition, the correlation of structural factors with the stability of chiral gold clusters was thoroughly evaluated by monitoring the CD, UV-vis, and NMR spectra at elevated temperatures. Insight into the relationship between the structural factors with the chiroptical property and stability of chiral gold clusters in this work will help us to design and achieve more stable chiral metal clusters and stimulate their practical applications in chiroptical functional materials.

Self-Assembly of Molecular Trefoil Knots Featuring Pentadecanuclear Homoleptic AuI -, AuI /AgI -, or AuI /CuI -Alkynyl Coordination.

Metal-free and metal-containing molecular trefoil knots are fascinating ensembles that are usually covalently assembled, the latter requiring the rational design of di- or multidentate/multipodal ligands as connectors. In this work, we describe the self-assembly of pentadecanuclear AuI trefoil knots [Au15 (C≡CR)15 ] from monoalkynes HC≡CR (R=9,9-X2 -fluorenyl with X=nBu, n-hexyl) and [AuI (THT)Cl]. Hetero-bimetallic counterparts [Au9 M6 (C≡CR)15 ] (M=Cu/Ag) were self-assembled by reactions of [Au15 (C≡CR)15 ] with [Cu(MeCN)4 ]+ /AgNO3 and HC≡CR. The type of pentadecanuclear trefoil knots described herein is characterized by X-ray crystallography, 2D NMR and HR-ESI-MS. [Au9 Cu6 (C≡CR)15 ] is relatively stable in hexane; its excited state properties were investigated. DFT calculations revealed that non-covalent metal-metal and metal-ligand interactions, together with longer alkyl chain-strengthened inter-ligand dispersion interactions, govern the stability of the trefoil knot structures.