Transition Metal Clusters Research Articles

Prediction Descriptor for Catalytic Activity of Platinum Nanoparticles/Metal-Organic Framework Composites.

Supported metal nanoparticles (MNPs) have exhibited superior catalytic performance in various heterogeneous catalysis applications, which is usually influenced or even determined by the physicochemical properties of their porous supports. It is well acknowledged that understanding the regulation mechanism of supports is an important prerequisite to predict the catalytic performance of supported MNPs as well as the development of advanced catalysts. Here, we demonstrated that different transition-metal clusters (from Group IIIB to Group IIB) within metal-organic frameworks (MOFs) could accurately regulate the surface electronic status of supported platinum nanoparticles (Pt NPs), and the Pt/MOF composites showed a periodic activity trend in hydrogenation of 1-hexene. A strong correlation was found between the catalytic activity of Pt/MOF composites and the number of electrons in their outmost d orbitals of the transition-metal species, suggesting that the latter could play the role of prediction descriptor. Furthermore, this descriptor can be extended to predict the hydrogenation activity of more Pt/MOF composites and provide an important guiding principle for the design of supported MNPs catalysts.

Ab initio investigation of the adsorption of phenolic compounds, CO, and H[formula omitted]O over metallic cluster/silica catalysts for hydrodeoxygenation process

The catalytic hydrodeoxygenation (HDO) of lignin is an important route to produce green aromatics. Herein we study the adsorption of key phenolic molecules (phenol, catechol, guaiacol, anisole) over various metallic nanoparticles (NP) (Ni, Cu, Co, Fe) supported over amorphous silica, by the periodic spin polarized density functional theory (DFT). CO and water are potential inhibiting molecules present in the lignin pyrolysis gas. Therefore their competing adsorption is also studied in details. Our calculations show that the oxygenated compounds have a stronger interaction at the interface between the NP cluster and the silica for all the studied metals. By comparing the resulting adsorption energies, we found that the Ni13@silica catalyst is the most attractive one for oxygenated molecules. The most stable configuration is a phenol adsorption at the interface through the OH group with the silica surface and the aromatic ring with the transition metal cluster. In addition, we show that the adsorption of the oxygenated compounds is not impacted by the presence of inhibiting molecules on Fe13@silica, Co13@silica and Ni13@silica catalysts. This type of DFT investigation appears to be useful to suggest suitable formulations for an optimal HDO of lignin.

Linear and nonlinear machine learning correlation of transition metal cluster characteristics

Linear and nonlinear machine learning correlation of transition metal cluster characteristics

Evidence of cluster formation of croconic acid with Ag, Au and Cu cages, enhancement of electronic properties and Raman activity

Investigation of the adsorption properties croconic acid (CCA) with metal clusters (mC: Ag, Au and Cu) are reported using DFT method. CCA is found to form stable cluster with transition metal clusters of copper, silver and gold. The drug-cluster complexaton energy is slightly more for the copper nanocluster-drug complex. Non-covalent interaction analysis indicated that strong interactions and weak van der Waal interaction is present between drug and metal clusters. Dipole moment of the drug-gold cluster is found to be higher than that of the other systems. SERS studies demonstrates improved Raman signals for multiple wavenumbers of all CCA-metal cluster complexes. Mulliken charge analysis show that all CCA oxygen atom’s charge changes due to the interactions with the mCs. Clustering of CCA with metal cages enhances the medicinal properties and the metal nanoclusters will act as a drug carrier of CCA.

Magnetic coupling in oximato bridged {MnIII6} clusters bridged by diamagnetic dicyano-metallato linkers: A theoretical perspective

Oximato bridged {MnIII6} clusters are among the best known SMMs for transition metal clusters that exhibit a very large barrier height for magnetization reversal and decent blocking temperatures. Several attempts were made to improve the magnetic properties of this family, among others, employing dicyano-metallo linkers such as [Au/Ag(CN)2]- to link two {MnIII6} clusters gained attention as this paves the way forward to construct supramolecular architecture based on {MnIII6} units and also facilitate a way to control the intercluster exchange coupling – a parameter vital to Qubit application. In this work, we have employed DFT calculations to estimate various exchange coupling constants within the {MnIII6} clusters ([MnIII6(μ3-O)2(Et-sao)6(3-py)2(MeOH)2 (M(CN)2)2] M = Au (1), Ag (2) here sao2- is the dianion of salicylaldoxime or 2-hydroxybenzaldeyhyde oxime). We have identified four different Js within the cluster based on the orientation of the Jahn-Teller axes and the MnNOM dihedral angles. The computed J values within the clusters are in the borderline of ferro and antiferromagnetic coupling, leading to a competing interaction within the cluster, and for this reason, several spin states are found to lie close to each other. The computed Js reproduce the experimental susceptibility data and yield very small/negligible {MnIII6-MI-MnIII6} intercluster interaction. The reason for such weak couplings was analysed, and a search for stronger exchange coupling was undertaken by studying in detail the J values in [{Mn(salen)(EtOH)}3{M(CN)6}] (here M = FeIII (3), CrIII (4); Salen = N,N′-bis(salicylidene)ethylenediamine) clusters. This predictive strategy suggests that incorporating a metal ion such as CrIII could be a game-changer as this promotes a very strong ferromagnetic coupling between two MnIII centers. If this prediction is attempted for oximato bridged {MnIII6} clusters, it could be very rewarding.

Resolution of Low-Energy States in Spin-Exchange Transition-Metal Clusters: Case Study of Singlet States in [Fe(III)4S4] Cubanes.

Polynuclear transition-metal (PNTM) clusters owe their catalytic activity to numerous energetically low-lying spin states and stable oxidation states. The characterization of their electronic structure represents one of the greatest challenges of modern chemistry. We propose a theoretical framework that enables the resolution of targeted electronic states with ease and apply it to two [Fe(III)4S4] cubanes. Through direct access to their many-body wave functions, we identify important correlation mechanisms and their interplay with the geometrical distortions observed in these clusters, which are core properties in understanding their catalytic activity. The simulated magnetic coupling constants predicted by our strategy allow us to make qualitative connections between spin interactions and geometrical distortions, demonstrating its predictive power. Moreover, despite its simplicity, the strategy provides magnetic coupling constants in good agreement with the available experimental ones. The complexes are intrinsically frustrated anti-ferromagnets, and the obtained spin structures together with the geometrical distortions represent two possible ways to release spin frustration (spin-driven Jahn–Teller distortion). Our paradigm provides a simple, yet rigorous, route to uncover the electronic structure of PNTM clusters and may be applied to a wide variety of such clusters.

Tetrahedral Pt10– Cluster with Unique Beta Aromaticity and Superatomic Feature in Mimicking Methane

Utilizing a customized metal cluster source in tandem with a flow tube reactor and a reflectron time-of-flight mass spectrometer, we have obtained well-resolved pure metal clusters Ptn- and observed their gas-phase reactions with a few small gas molecules. Interestingly, the remarkable inertness of Pt10- was repeatedly observed in different reactions. Meanwhile, we have determined the structure of Pt10- within a regular tetrahedron. Considering that Pt possesses 5d96s1 electron configuration, the tetrahedral Pt10- exhibits unexpected stability at neither a magic number of valence electrons nor a shell closure of geometric structure. Comprehensive theoretical calculations unveil the stability of Pt10- is significantly associated with the all-metal aromaticity. In addition to the classical total aromaticity, which is mainly due to 6s electrons, there is unique beta-aromaticity ascribed to spin-polarized beta 5d electrons pertaining to singly occupied multicenter bonds. Further, we demonstrate the superatomic feature of such a transition metal cluster Pt10-, as Pt6@Pt4-, in mimicking methane.

Energy Decomposition to Access the Stability Changes Induced by CO Adsorption on Transition-Metal 13-Atom Clusters.

Our atomistic understanding of the physical-chemical parameters that drives the changes in the relative stability of clusters induced by adsorbed molecules is far from satisfactory. In this work, we employed density functional theory calculations to address this problem using CO adsorption on 13-atom transition-metal clusters, TM13, namely, nCO/TM13, where TM = Ru, Rh, Pd, and Ag, and n = 1-6. Unexpectedly, changes in the relative stability take place for all systems at a lower coverage, namely, at n = 3 (Ru13), 4 (Rh13, Ag13), and 2 (Pd13). To address the effects that lead to changes in the stability, we proposed an energy decomposition scheme for the binding energy of the nCO/TM13 systems, which yields that the change in relative stability is dominated by the interaction energy and cluster distortion energy upon adsorption, where the interaction energy is higher for high-energy unprotected clusters. Furthermore, we characterized all adsorption parameters, which helps us to complement our atomistic understanding.

Lawrence F. Dahl

Lawrence F. Dahl, 91, died March 20 in Madison, Wisconsin. “Professor Dahl’s research focused on inorganic chemistry, with an emphasis on the synthesis of well-defined transition-metal cluster comp...

A comparative study on the reactivity of cationic niobium clusters with nitrogen and oxygen

We have prepared well-resolved Nbn+ (n = 1–10) clusters and report here an in-depth study on the essentially different reactivity with N2 and O2, by utilizing a multiple-ion laminar flow tube reactor in tandem with a customized triple quadrupole mass spectrometer (MIFT-TQMS). As results, the Nbn+ clusters are found to readily react with N2 and form adsorption products NbnN2m+; in contrast, the reactions with O2 give rise to NbnO1−4+products, and the odd-oxygen products indicate O-O bond dissociation, as well as increased mass abundance of NbO+ pertaining to oxygen-etching reactions. We illustrate how N2 prefers a physical adsorption on Nbn+clusters with an end-on orientation for all the products, and allow for size-selective Nbn+clusters to act as electron donor or acceptor in forming NbnN2m+. In contrast to these nitrides, the dioxides NbnO2+display much larger binding energies, with O2 always as an electron acceptor, corresponding to superoxide or peroxide states in the initial reactions. Density-of-states and orbital analyses show that the interactions between Nbn+ and O2 are dominated by strong π-backdonation indicative of incidental electron transfer; whereas weak π-backdonation and simultaneous σ donation interactions exist in NbnN2+. Further, reaction dynamics analysis illustrates the different interactions for N2 and O2 in approaching the Nbn+ clusters, showing the energy diagrams for N2 adsorption and O-O bond dissociation in producing odd-oxygen products. Fragment analyses with orbital correlation and donor-acceptor charge transfer are also performed, giving rise to full insights into the reactivities and interactions of such transition metal clusters with typical diatomic molecules.

Theoretical Analysis of the Dynamical Effects of the Amino Acid Residue Replacement in the Vicinity of the [4Fe–4S] Proximal Cluster on the O2-Tolerance of [NiFe]-Hydrogenases

Hydrogenases are enzymes that catalyze the reversible reaction, \(\text{H}_{2} \rightleftharpoons 2\text{H}^{ + } + 2\text{e}^{ - }\), that occurs at the transition metal cluster in the catalytic c...

On-surface preparation of coordinated lanthanide-transition-metal clusters

The study of lanthanide (Ln)-transition-metal (TM) heterometallic clusters which play key roles in various high-tech applications is a rapid growing field of research. Despite the achievement of numerous Ln-TM cluster compounds comprising one Ln atom, the synthesis of Ln-TM clusters containing multiple Ln atoms remains challenging. Here, we present the preparation and self-assembly of a series of Au-bridged heterometallic clusters containing multiple cerium (Ce) atoms via on-surface coordination. By employing different pyridine and nitrile ligands, the ordered coordination assemblies of clusters containing 2, 3 and 4 Ce atoms bridged by Au adatoms are achieved on Au(111) and Au(100), as revealed by scanning tunneling microscopy. Density functional theory calculations uncover the indispensable role of the bridging Au adatoms in constructing the multi-Ce-containing clusters by connecting the Ce atoms via unsupported Ce-Au bonds. These findings demonstrate on-surface coordination as an efficient strategy for preparation and organization of the multi-Ln-containing heterometallic clusters.

Structure and magnetic properties of one carboxylate-bridged linear trinuclear [Ni3] and one paddle-wheel dinuclear [Cu2] cluster

Two carboxylate-bridged transition metal clusters, trinuclear [Ni3(CPA)6(bipy)2] (1) and dinuclear [Cu2(CPA)4(DMSO)2] (2), have been successfully prepared respectively based on mixed ligands of 4-chlorophenylacetic acid (HCPA) and 2,2′-bipyridine (bipy) or the single ligand of HCPA. Single crystal X-ray diffraction analyses reveal that complex 1 crystallizes in triclinic P-1 space group and has a structure of linear trinuclear [Ni3] cluster, and 2 crystallizes in monoclinic P21/n space group and includes a paddle-wheel dinuclear [Cu2] entity. The magnetic susceptibilities of 1 and 2 were quantitatively analyzed based on a linear trinuclear [Ni3] model with Hamiltonian Ĥ = -JŜ1Ŝ2-JŜ2Ŝ3 and a dimer [Cu2] model with Ĥ = -JŜ1Ŝ2, respectively, resulting in g = 2.18(1), J = -0.79(1) cm−1 for 1 and g = 2.19(1), J = -321(1) cm−1 for 2. These confirms that the neighboring spin centers both display antiferromagnetic coupling in 1 and 2.

Metal-rich metallaboranes: Clusters containing triply and tetra bridging borylene and boride units

Metal-rich metallaborane clusters, having triply and tetra bridging borylenes, and multicentred boride units are demanding renewed interest because of their diverse reactivity and unique structural features. Recent years have witnessed significant progress in the field of metal-rich metallaborane clusters. In spite of high instability of free borylene species, modern synthetic strategies utilizing transition metals have enabled to the isolation of borylene species, particularly as triply bridging borylene species. On the other hand, naked boron ‘boride’ has been encapsulated inside different types of transition metal and metallaborane clusters. The unique bonding ability of the boron of borylene and boride with multiple transition metals afforded a series of metal-rich metallaboranes. In this review, we have discussed the history of the synthesis of metal-rich clusters containing triply bridging borylene and boride moieties and their structure, bonding, and electron count. The reactivity of these metal-rich metallaboranes toward various substrates has also been discussed.

Adsorption of transition metal clusters on Boron-graphdiyne

Layered carbon materials can be useful as supports for catalytic metallic nanoparticles in different applications. Also, doping porous carbons with metal atoms and nanoparticles enhances the hydrogen storage capacity of those materials. We have investigated the adsorption of transition metal atoms and small clusters on boron graphdiyne (BGDY) using density functional theory. This layered material contains uniformly distributed large hexagonal holes that can host the metal clusters. Single V, Co and Pd atoms sit at the hexagon corners, near the B atoms. Their binding energies are large enough to make the systems suitable for single-atom catalysis but atomic diffusion cannot be overlooked. Formation of dimers of those three elements near the hexagon corners is preferred over decoration by two separated atoms. The octahedral structure of the free hexamers is preserved on adsorption of V6 and Co6, but it changes in Pd6. The adsorption sites of the three hexamers are different. The adsorption energies of single atoms, dimers and hexamers on BGDY are substantially larger than those on pristine graphene, and similar to those on graphdiyne, but the larger holes existing in BGDY make this system better tuned for some applications.

Decavanadate-based clusters as bifunctional catalysts for efficient treatment of carbon dioxide and simulant sulfur mustard

Reutilization of carbon dioxide (CO2) and destruction of chemical warfare agents (CWAs) at ambient conditions are deemed as two of the crucial challenges to steer toward a more sustainable future because they can cause great hazard to human beings and environment. Design of stable, selective and powerful catalysts for multi-functional catalysis is highly desirable yet largely unmet. In this work, a series of novel decavanadate-based transition metal clusters (POVs-TM, compounds 1–5) have been reported. Compounds 1–5 possess decavanadate-centered structures in which one decavanadate cluster bridged two bridged or free transition metal units. Decavanadate unit, serving as redox center can construct bifunctional catalysis platform with transition metal. Thus-obtained clusters can serve as powerful bifunctional catalysts in both cycloaddition of CO2 and degradation of sulfur mustard simulant. Specially, compound 1 presented high performance (conv. up to 99.4 %, sele. up to 99.5 %) in chemical fixation of CO2 into valuable cyclic carbonates with simulated flue gas as the gas resource. Besides, compound 3 performed superior efficiency (conv. 98.9 %, sele. 98.7 %) than other catalysts in the degradation of sulfur mustard simulant under ambient conditions. These dual-function validated POVs-TM clusters hold much promise in the exploration of novel catalysts for applications like continuous catalytic or flow bed reactions.

Systematic cluster growth: a structure search method for transition metal clusters.

The systematic cluster growth (SCG) method is a biased structure search strategy based on a seeding process for investigating the structural evolution and growth pattern of transition metal clusters. In SCG, a set of initial structures with size n are constructed based on the equilibrium structures of the preceding n- 1 cluster isomers by adding a single atom at all inequivalent binding sites. This strategy requires a relatively low number of evaluations for global minima localization on the potential energy surface, allowing its application in first-principles calculations. The performance of SCG is tested by using the Lennard Jones (LJ) potential energy surface. The 93.7% of the best-known solutions for Lennard Jones clusters were found for n≤ 80 by using a relatively low number of local optimizations. Most importantly, by using SCG combined with DFT calculations (SCG-DFT), we revisit and provide the ground state structures and growth pattern for transition metal clusters TMn (where TM = Ti, Ni, Cu, Ag, Pt; and n = 6-14). The application of the code for doped clusters is also discussed. A detailed description of the present method for generating the structures of the clusters is provided.

Theoretical insights into C-H bond activation of methane by transition metal clusters: the role of anharmonic effects.

In heterogeneous catalysis, the determination of active phases has been a long-standing challenge, as materials' properties change under operational conditions (i.e. temperature (T) and pressure (p) in an atmosphere of reactive molecules). As a first step towards materials design for methane activation, we study the T and p dependence of the composition, structure, and stability of metal oxide clusters in a reactive atmosphere at thermodynamic equilibrium using a prototypical model catalyst having wide practical applications: free transition metal (Ni) clusters in a combined oxygen and methane atmosphere. A robust methodological approach is employed, where the starting point is systematic scanning of the potential energy surface (PES) to obtain the global minimum structures using a massively parallel cascade genetic algorithm (cGA) at the hybrid density functional level. The low energy clusters are further analyzed to estimate their thermodynamic stability at realistic T, pO2 and pCH4 using ab initio atomistic thermodynamics (aiAT). To incorporate the anharmonicity in the vibrational free energy contribution to the configurational entropy, we evaluate the excess free energy of the clusters numerically by a thermodynamic integration method with ab initio molecular dynamics (aiMD) simulation inputs. By analyzing a large dataset, we show that the conventional harmonic approximation miserably fails for this class of materials, and capturing the anharmonic effects on the vibration free energy contribution is indispensable. The latter has a significant impact on detecting the activation of the C–H bond, while the harmonic infrared spectrum fails to capture this, due to the wrong prediction of the vibrational modes.

Ab initio investigation of the role of the d-states occupation on the adsorption properties of H2, CO, CH4 and CH3OH on the Fe13, Co13, Ni13 and Cu13 clusters

Here, we report a theoretical investigation, based on density functional theory calculations, into the role of the occupation d-states on the adsorption properties of CH4, CO, H2 and CH3OH on 3d 13-atom transition-metal (TM13) clusters (TM = Fe, Co, Ni, Cu). Except for Cu13, a gradual increase in the occupation of the d-states, i.e., from Fe13 to Ni13, increases the magnitude of the adsorption energy almost linearly for the H2/TM13 and CO/TM13 systems, which can be explained by the enhancement of the sp-d hybridization due to the shift of the d-states towards the highest occupied molecular orbital (HOMO). For Cu13, the d-states are located well below the HOMO, which reduces the sp-d hybridization, and hence, a smaller adsorption energy is obtained. However, this picture does not hold for CH4/TM13 and CH3OH/TM13, where the adsorption energy has nearly the same value for all TM13 clusters, which can be explained by electrostatic effects such as local polarization of the molecules and nearby TM atoms, and hence, the basic features of physisorption systems. Based on the electron density difference, the polarization effects are slightly larger for systems with empty d-states.

Au101-rGO nanocomposite: immobilization of phosphine-protected gold nanoclusters on reduced graphene oxide without aggregation.

Graphene supported transition metal clusters are of great interest for potential applications, such as catalysis, due to their unique properties. In this work, a simple approach to deposit Au101(PPh3)21Cl5 (Au101NC) on reduced graphene oxide (rGO) via an ex situ method is presented. Reduction of graphene oxide at native pH (pH ≈ 2) to rGO was performed under aqueous hydrothermal conditions. Decoration of rGO sheets with controlled content of 5 wt% Au was accomplished using only pre-synthesised Au101NC and rGO as precursors and methanol as solvent. High resolution scanning transmission electron microscopy indicated that the cluster size did not change upon deposition with an average diameter of 1.4 ± 0.4 nm. It was determined that the rGO reduction method was crucial to avoid agglomeration, with rGO reduced at pH ≈ 11 resulting in agglomeration. X-ray photoelectron spectroscopy was used to confirm the deposition of Au101NCs and show the presence of triphenyl phosphine ligands, which together with attenuated total reflectance Fourier transform infrared spectroscopy, advocates that the deposition of Au101NCs onto the surface of rGO was facilitated via non-covalent interactions with the phenyl groups of the ligands. Inductively coupled plasma mass spectrometry and thermogravimetric analysis were used to determine the gold loading and both agree with a gold loading of ca. 4.8–5 wt%. The presented simple and mild strategy demonstrates that good compatibility between size-specific phosphine protected gold clusters and rGO can prevent aggregation of the metal clusters. This work contributes towards producing an agglomeration-free synthesis of size-specific ligated gold clusters on rGO that could have wide range of applications.