Transition Metal Clusters Research Articles

Tunable interaction between metal clusters and graphene

We describe the interaction between small transition metal clusters and graphene using first principles calculations. The coupling is analyzed in terms of different features of the system: binding energy, decomposition into atomic orbitals, the presence of defects on the graphene layer, and both the band and geometrical structures. The binding strength is found to follow the d-band model, which anticipates the binding energies of clusters on graphene layers from the position of the cluster's d-band centers relative to the their highest-occupied and lowest-unoccupied molecular orbital levels. These findings are verified for 6-atom and 13-atom transition metal clusters (Ti, Pd, Pt, and Au) and considering different types of defects. The adhesion of the TM clusters is substantially larger on defective graphene layers than on pristine ones. Buckling of the graphene layer may arise from the presence of defects but it does not necessarily imply strong binding. However, buckling can sometimes offer configurational paths through which the adsorbed cluster is stabilized changing its original shape. Insights into this work offer mechanisms to tailor the electronic properties of the combined nanoparticle-graphene system by changing the size and composition of transition metal clusters.

Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of Chalcogenidoplumbates(II or IV).

The phases of "PbCh2" (Ch = Se, Te) are obtained from solid-state syntheses (i.e., by the fusion of the elements under inert conditions in silica glass ampules). Reduction of such phases by elemental alkaline metals in amines affords crystalline chalcogenidoplumbate(II) salts comprised of [PbTe3]2- or [Pb2Ch3]2- anions, depending upon which sequestering agent for the cations is present: crown ethers, like 18-crown-6, or cryptands, like [2.2.2]crypt. Reactions of solutions of such anions with transition-metal compounds yield (poly-)chalcogenide anions or transition-metal chalcogenide clusters, including one with a µ-PbSe ligand (i.e., the heaviest-known CO homolog). In contrast, the solid-state synthesis of a phase of the nominal composition "K2PbSe2" by successive reactions of the elements and by the subsequent solvothermal treatment in amines yields the first non-oxide/halide inorganic lead(IV) compound: a salt of the ortho-selenidoplumbate(IV) anion [PbSe4]4-. This was unexpected due to the redox potentials of Pb(IV) and Se(-II). Such methods can further be applied to other elemental combinations, leading to the formation of solutions with binary [HgTe2]2- or [BiSe3]3- anions, or to large-scale syntheses of K2Hg2Se3 or K3BiSe3 via the solid-state route. All compounds are characterized by single-crystal X-ray diffraction and elemental analysis; solutions of plumbate salts can be investigated by 205Pb and 77Se or 127Te NMR techniques. Quantum chemical calculations using density functional theory methods enable energy comparisons. They further allow for insights into the electronic configuration and thus, the bonding situation. Molecular Rh-containing Chevrel-type compounds were found to exhibit delocalized mixed valence, whereas similar telluridopalladate anions are electron-precise; the cluster with the µ-PbSe ligand is energetically favored over a hypothetical CO analog, in line with the unsuccessful attempt at its synthesis. The stability of formal Pb(IV) within the [PbSe4]4- anion is mainly due to a suitable stabilization within the crystal lattice.

Crystallizing Elusive Chromium Polycations

Summary Metal-oxo clusters are commonly isolated from water with ligands for preventing the precipitation of metal hydroxides. However, unligated clusters are important for both mechanistic studies and applications. Isolating open-shell transition-metal clusters is especially difficult without ligation. Herein, we elucidate a cluster-isolation process that yields an unligated Zn 2+ -Al 3+ -Cr 3+ polyoxocation. For decades, Cr 3+ -polyoxocations have proved elusive synthetic targets because of hydrolytic instability. We overcame the synthetic challenges by the following strategies: (1) pH-driven hydrolysis by oxidative dissolution of zinc; (2) metal nitrate concentrations 10× higher than conventional syntheses, suppressing cluster assembly; and (3) azeotropic evaporation of HNO 3 -H 2 O, driving cluster assembly and crystallization at the solution surface. Contrary to common cluster growth, the fully assembled cluster is never detected in the reaction solution. Because these reactive clusters do not persist in solution, uncontrolled precipitation of metal hydroxide is avoided. The proposed formation pathway opens opportunities to expand the composition space of metal-oxo clusters.

Large adsorption energies for CO on Scn (n = 2−8, 13) nanoclusters**Project supported by the Natural Science Foundation of Tibet Autonomous Region, China (Grant No. 2016-ZR-15-23), the Fund from the Key Laboratory of Optical Information Processing and Visualization Technology, Tibet Autonomous Region, China, the Young Talent Cultivation Plan of Xizang (Tibet) Minzu University, China (Grant No. 14myQP05), and the Important

In order to seek a transition metal cluster with high ability to adsorb CO molecule, the author performs a density function theory calculation on COScn (n = 2–8, 13) clusters. The results demonstrate that COScn (n = 2–8, 13) clusters have the large adsorption energies of which the values are over 3.6 eV, and the elongations of C–O bond length exceed 20% in most calculated sizes. Adsorbing CO contributes to the improvement of the chemical activity, but reduces the magnetic moment of corresponding Scn cluster.

Sequential bonding of CO molecules to a titanium dimer: A photoelectron velocity-map imaging spectroscopic and theoretical study of Ti2(CO)n- (n = 1-9).

Binuclear titanium carbonyl cluster anions, Ti2(CO)n- (n = 4-6), are produced via a laser vaporization supersonic cluster source and characterized by mass-selected photoelectron velocity-map imaging spectroscopy. Quantum chemical calculations are carried out for Ti2(CO)n- (n = 1-9) to explore the trend of sequential bonding of CO molecules to a titanium dimer. It has been found that the CO molecules bind to Ti2 in a side-on fashion and form a stable Ti2[η2(μ2-C, O)]3 structure at n = 3, the motif of which retains up to n = 5. Starting at n = 6, a new building block of two CO groups side-on-bonded to Ti2 is favored, the structure of which persists up to n = 9. In the larger clusters (n = 6-9), the side-on-bonded CO molecule can be stabilized via the removal of two electrons from an anionic titanium carbonyl, which is different from the effect of charge on CO binding in rhodium carbonyls where bridge-bonded CO molecules are selectively destabilized by the removal of an electron from a neutral rhodium carbonyl. The present study provides a stepwise picture for molecular-level understanding of CO bonding on transition-metal clusters, which is directly relevant to the elementary processes of CO at metal catalysts.

ChemInform Abstract: Insights into Small Molecule Activation by Multinuclear First‐row Transition Metal Cyclophanates

AbstractReview: 98 refs.

Perspective: Quantum mechanical methods in biochemistry and biophysics.

In this perspective article, I discuss several research topics relevant to quantum mechanical (QM) methods in biophysical and biochemical applications. Due to the immense complexity of biological problems, the key is to develop methods that are able to strike the proper balance of computational efficiency and accuracy for the problem of interest. Therefore, in addition to the development of novel ab initio and density functional theory based QM methods for the study of reactive events that involve complex motifs such as transition metal clusters in metalloenzymes, it is equally important to develop inexpensive QM methods and advanced classical or quantal force fields to describe different physicochemical properties of biomolecules and their behaviors in complex environments. Maintaining a solid connection of these more approximate methods with rigorous QM methods is essential to their transferability and robustness. Comparison to diverse experimental observables helps validate computational models and mechanistic hypotheses as well as driving further development of computational methodologies.

Five Disk‐Shaped {MII7} (M = Mn, Fe, Co, Cu, Zn) Clusters and One Capsule‐Like {CuII6NaI2} Cluster Assembled from the Same Schiff Base Ligand

AbstractInvited for the cover of this issue is the group of Yahong Li at Soochow University, Suzhou, P. R. China. The cover image shows five disk‐shaped {M7} transition metal clusters and one capsule‐like {CuII6NaI2} cluster, whose magnetic properties are studied.

Vanadium and Chromium Molecular Cluster Batteries (MCB): Li- Storage in Transition Metal Complexes

Increasing energy demands and the requirement to reduce carbon dioxide emissions at the same time accelerated the world-wide research on renewable energy sources and energy storage. However, for future applications in personal electronics, electro-mobility and decentralised energy storage, new LIB electrode materials based on light-weight and earth abundant components with superior redox activity, long-term stability and high energy density are urgently required. The concept of using molecular transition metal clusters as active electrode materials for reversible Li ion shuttling opens up a new direction for energy storage.[1] These metal complexes are interesting electrode materials due to the ability of the transition metal ions to exist in several oxidation states and reversibly reacting with Li.[2,3] In this study we introduce LIBs based on molecular cluster systems of the early transition metal ions vanadium and chromium as the cathode active material, in a so-called molecular cluster battery (MCB). Transition metal complexes of different ligand systems were characterised by IR, XRD and SEM techniques. Their Li cycling behaviour was investigated by galvanostatic cycling and cyclic voltammetry (CV). High reversible specific capacities with low capacity loss were found and multi-step redox processes were observed reflecting the various oxidation states of these metal ions. The 2D channels of the crystalline compounds, which are revealed in their crystal packing diagram, are suitable for an easy Li ion transportation trough the structure. The Li ion diffusion coefficients were determined by various electrochemical techniques, such as GITT, CV and EIS to understand the Li ion kinetics of these molecular metal clusters. The various oxidation steps of molecular cluster compounds allow multi-step redox changes making these materials interesting compounds with potentially high specific capacities and allow a study of the kinetics of the lithium ion diffusion pathway.

Catalysis and Nuclear Magnetic Resonance Signal Enhancement with Parahydrogen

When catalytic hydrogenations use parahydrogen instead of normal H2, the NMR signals of reaction products and intermediates can be dramatically enhanced. This phenomenon, called parahydrogen-induced polarization (PHIP), has been used previously to address the mechanisms of H2 activation by transition metal complexes and clusters in solution. At the same time, it is highly desirable to combine this methodology with heterogeneous catalysis. Potential benefits of such combination include the possibility to develop a hypersensitive NMR-based tool for mechanistic studies of heterogeneous catalytic processes as well as to establish an efficient technology for the production of novel contrast agents for in vivo MRI. To achieve this, one needs to combine the ‘homogeneous’ hydrogenation mechanism, which incorporates both H atoms of a H2 molecule into the same product molecule, with the ease of catalyst removal and the possibility to perform the reaction in a continuous mode, the inherent features of heterogeneous catalysis. This field of NMR and MRI research can thus benefit from the current efforts at the interface between homogeneous and heterogeneous catalysis. Here, after a brief introduction of the PHIP phenomenon, the current progress in combining PHIP with heterogeneous hydrogenations is discussed, and future promising directions are outlined.

Subnano Pt Particles from a First-Principles Stochastic Surface Walking Global Search.

Subnano transition metal particles have wide applications in chemistry. For the complexity of their potential energy surface, it has long been a great challenge for both theory and experiment to determine the structure of subnano clusters and thus predict their physiochemical properties. Here we explore the structure configurations for 35 subnano PtN (N = 12-46) clusters using a first-principles Stochastic Surface Walking (SSW) global search. For each cluster, thousands of structure candidates are collected from a parallel SSW search. This leads to the finding of 20 new global minima in 35 clusters, which reflects the essence of a first-principles global search for revealing the structure of subnano transition metal clusters. PtN subnano clusters with N being 14, 18, 22, 27, 36, and 44 have higher stability than their neighboring size clusters and are characterized as magic number clusters. These PtN subnano clusters exhibit metallic characteristics with a diminishing HOMO-LUMO gap, much poorer binding energy (by 1-1.7 eV), and a much higher Fermi level (by 1-1.5 eV) than bulk metal, implying their high chemical activity. By analyzing their structures, we observe the presence of a rigid core and a soft shell for PtN clusters and find that the core-shell 3-D architecture evolves as early as N > 22. For these core-shell clusters, a good core-shell lattice match is the key to achieve the high stability.

Structure and energetics in dissociative electron attachment to HFeCo3(CO)12

Here we report structural parameters on the heteronuclear transition metal complex HFeCo3(CO)12 and its anion formed upon electron attachment, as well as the thermochemical thresholds for sequential CO loss and the loss of the apical group (as Fe(CO)- 3 and Fe(CO)- 4). Geometrical parameters from single crystal X-ray diffraction are compared with calculated values from density functional theory calculations, for the neutral and anionic ground state of this transition metal cluster. Further, experimental appearance energies for sequential CO loss and the formation of Fe(CO)- 3 and Fe(CO)- 4 are compared to the respective calculated threshold values. Geometry optimizations were performed at the BP86/def2-TZVP level of theory while the threshold energies were calculated at the PBE0/ma-def2-TZVP level of theory. The SOMO of the anion is found to have a clear Fe-Co anti-bonding character resulting in elongation of the Fe-Co bonds and the transformation of one of the terminal Co-CO groups to a bridging Co-CO-Fe group upon electron attachment. The thermochemical threshold PBE0 calculations are concordant with the observed appearance energies and structural parameters from single crystal X-ray diffraction for the neutral molecule are well reproduced at the BP86/def2-TZVP level of theory.

Diverse Ligand-Functionalized Mixed-Valent Hexamanganese Sandwiched Silicotungstates with Single-Molecule Magnet Behavior.

Under hydrothermal conditions, replacement of the water molecules in the [Mn(III) 4 Mn(II) 2 O4 (H2 O)4 ](8+) cluster of mixed-valent Mn6 sandwiched silicotungstate [(B-α-SiW9 O34 )2 Mn(III) 4 Mn(II) 2 O4 (H2 O)4 ](12-) (1 a) with organic N ligands led to the isolation of five organic-inorganic hybrid, Mn6 -substituted polyoxometalates (POMs) 2-6. They were all structurally characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, diffuse-reflectance spectroscopy, and powder and single-crystal X-ray diffraction. Compounds 2-6 represent the first series of mixed-valent {Mn(III) 4 Mn(II) 2 O4 (H2 O)4-n (L)n } sandwiched POMs covalently functionalized by organic ligands. The preparation of 1-6 not only indicates that the double-cubane {Mn(III) 4 Mn(II) 2 O4 (H2 O)4-n (L)n } clusters are very stable fragments in both conventional aqueous solution and hydrothermal systems and that organic functionalization of the [Mn(III) 4 Mn(II) 2 O4 (H2 O)4 ](8+) cluster by substitution reactions is feasible, but also demonstrates that hydrothermal environments can promote and facilitate the occurrence of this substitution reaction. This work confirms that hydrothermal synthesis is effective for making novel mixed-valent POMs substituted with transition-metal (TM) clusters by combining lacunary Keggin precursors with TM cations and tunable organic ligands. Furthermore, magnetic measurements reveal that 3 and 6 exhibit single-molecule magnet behavior.

Combinatorics of Petersen graph and its compositions for all irreducible representations for Jahn–Teller, non-rigid molecules and clusters

We have considered the combinatorics of the Petersen graph and its various compositions with other graphs for all irreducible representations (IRs) of the corresponding automorphism groups. These graphs represent Berry pseudorotation of the trigonal bipyrmidal (TBP) molecules, clusters such as $$\hbox {Ta}_{5}$$ , and non-rigid ligands placed at the corners of the TBP structure. We have computed the properties for coloring combinatorics for the vertices, edges, and pentagons of the Petersen graph for all IRs for up to six different color types. Compositions of the Petersen graphs with other graphs have also been considered with complete enumeration tables obtained for the composition of the Petersen graph with $$\hbox {K}_{2}$$ containing 122,880 elements and 136 conjugacy classes. Such compositions of the Petersen graph represent the automorphism groups of the isomerization graphs of pentacoordinated TBP molecules and transition metal clusters such as $$[\hbox {Co}(\hbox {H}_{2}\hbox {O})_{5}]^{3+}$$ , pentacoordinated transition metal-ammonia complexes, organometallic systems such as $$\hbox {Sb}(\hbox {CH}_{3})_{5}$$ etc., all of which exhibit isomerization graphs that have wreath product automorphisms. Coloring tables of such graphs under their group actions are also constructed.

The Main Group Elements, Fragments, Compounds and Clusters Obey the 4n Rule and Form 4n Series: They are Close relatives to Transition Metal Counterparts via the 14n Linkage

<p>The paper presents numbers which were derived from 4n-based series in a matrix table. The numbers agree precisely with the total number of valence electrons surrounding the respective skeletal elements. The series approach focuses mainly on the number of skeletal elements and their respective number of valence electron content regardless of the origin of the electrons and the type of skeletal elements. For instance, any 6 skeletal elements of transition metal carbonyls surrounded by 86 valence electrons coded as (6,86), series S = 14n+2 normally adopt an octahedral geometry whereas (6,26) series S = 4n+2 for main group elements also tend to adopt an octahedral shape. The transition metal carbonyl cluster series were extensively covered in our previous articles. This paper demonstrates that the main group fragments, clusters and molecules which we normally explain by terms such as valency, valence electrons and octet rule also obey the 4n-based series. The fragments, molecules and clusters of the main group elements correspond well to those of respective transition metal clusters especially the carbonyls if the masking electrons are removed from them. Hence, the series approach is a qualitative method that acts as a unifier of some transition metal clusters with some main group elements clusters.</p>

Designed Assembly of Heterometallic Cluster Organic Frameworks Based on Anderson-Type Polyoxometalate Clusters.

A new approach to prepare heterometallic cluster organic frameworks has been developed. The method was employed to link Anderson-type polyoxometalate (POM) clusters and transition-metal clusters by using a designed rigid tris(alkoxo) ligand containing a pyridyl group to form a three-fold interpenetrated anionic diamondoid structure and a 2D anionic layer, respectively. This technique facilitates the integration of the unique inherent properties of Anderson-type POM clusters and cuprous iodide clusters into one cluster organic framework.

SparseMaps--A systematic infrastructure for reduced-scaling electronic structure methods. III. Linear-scaling multireference domain-based pair natural orbital N-electron valence perturbation theory.

Multi-reference (MR) electronic structure methods, such as MR configuration interaction or MR perturbation theory, can provide reliable energies and properties for many molecular phenomena like bond breaking, excited states, transition states or magnetic properties of transition metal complexes and clusters. However, owing to their inherent complexity, most MR methods are still too computationally expensive for large systems. Therefore the development of more computationally attractive MR approaches is necessary to enable routine application for large-scale chemical systems. Among the state-of-the-art MR methods, second-order N-electron valence state perturbation theory (NEVPT2) is an efficient, size-consistent, and intruder-state-free method. However, there are still two important bottlenecks in practical applications of NEVPT2 to large systems: (a) the high computational cost of NEVPT2 for large molecules, even with moderate active spaces and (b) the prohibitive cost for treating large active spaces. In this work, we address problem (a) by developing a linear scaling "partially contracted" NEVPT2 method. This development uses the idea of domain-based local pair natural orbitals (DLPNOs) to form a highly efficient algorithm. As shown previously in the framework of single-reference methods, the DLPNO concept leads to an enormous reduction in computational effort while at the same time providing high accuracy (approaching 99.9% of the correlation energy), robustness, and black-box character. In the DLPNO approach, the virtual space is spanned by pair natural orbitals that are expanded in terms of projected atomic orbitals in large orbital domains, while the inactive space is spanned by localized orbitals. The active orbitals are left untouched. Our implementation features a highly efficient "electron pair prescreening" that skips the negligible inactive pairs. The surviving pairs are treated using the partially contracted NEVPT2 formalism. A detailed comparison between the partial and strong contraction schemes is made, with conclusions that discourage the strong contraction scheme as a basis for local correlation methods due to its non-invariance with respect to rotations in the inactive and external subspaces. A minimal set of conservatively chosen truncation thresholds controls the accuracy of the method. With the default thresholds, about 99.9% of the canonical partially contracted NEVPT2 correlation energy is recovered while the crossover of the computational cost with the already very efficient canonical method occurs reasonably early; in linear chain type compounds at a chain length of around 80 atoms. Calculations are reported for systems with more than 300 atoms and 5400 basis functions.

Dehydrogenation of propylene mediated by CeVO4+: An interesting example for the chemistry of binary Ce–V transition-metal oxide cluster cations

Laser-ablation-generated cerium-vanadium oxide cluster cations CeVO4+ were mass-selected by applying a quadrupole mass filter, and reacted with propylene in a linear ion trap reactor at ambient conditions. Time-of-flight mass spectrometry and density functional theory calculations were used to characterize the cluster reactions. The CeVO4+ cluster has a closed-shell electronic structure, and is reactive toward propylene leading to the formation of CeVO3C3H4+/H2O and CeVO4C3H6+. The computed results indicate that this reaction involves the occurrence of spin conversions (singlet→triplet), and a new mechanism of dehydrogenation of alkenes, which is different from the reported ones, was proposed. Compared with another closed-shell cluster V3O7+, possessing the similar mass with CeVO4+, the heteronuclear oxide cluster cations show higher reactivity toward propylene. The computational results are in good agreement with the experimental observations. This work provides insights into nature of active sites and reaction mechanisms in related condensed-phase systems at a molecular level.

ChemInform Abstract: Recent Progress in Polyoxoniobates Decorated and Stabilized via Transition Metal Cations or Clusters

AbstractReview: 115 refs.

ChemInform Abstract: Resolving the Manganese Oxidation States in the Oxygen‐Evolving Catalyst of Natural Photosynthesis

AbstractReview: 154 refs.