Organometallic Clusters Research Articles

Large-scale simulations of the finite-temperature properties of the molecular assemblies Mn6 and Ni12

The numerical transfer-matrix approach and the exact diagonalization technique are worked out for the isotropic Heisenberg model with the uniform and alternating spin variables within the ring geometry. They are applied in large-scale simulations to the above cyclic organometallic clusters Mn6 (i.e. [Mn(hfac)2NITPh]6) and Ni12 (i.e. Ni12(O2CMe)12(chp)12(H2O)6(THF)6) in order to quantitatively model their magnetic properties. For the Ni12 complex new experimental data are also reported. The microscopic spin model parameters for both molecules are obtained from a fit of the theoretical curves to the experimental results.

Mechanistic Studies of the Hydrogenation of Alkynes with Os3(CO)10(μ-H)2 Using para-Hydrogen as a Probe

The reactions of 1-pentyne and acetylene with Os3(CO)10(μ-H)2 in the presence of para-H2 at 3−4 atm and 50−60 °C have been studied. An attempt is made to understand the nature of the intermediates in the catalytic hydrogenation process and the mechanistic relationship of the various organometallic clusters formed to each other and to the overall hydrogenation process. It was found that of the four products usually formed by the reaction of terminal alkynes with Os3(CO)10(μ-H)2, only the σ-π-vinyl complex Os3(CO)10(μ-η2-CHCHR)(μ-H) (A R = H or n-Pr) goes on to yield alkene and the starting Os3(CO)10(μ-H)2. The μ-η2-acetylido complex Os3(CO)10(μ-η2-CCR)(μ-H) (B), a product that results from the loss of hydrogen, is not formed under these conditions, as might be expected, in the presence of excess H2. The μ3-η2-alkyne complex Os3(CO)9(m-CO)(μ3-η2-HCCR) (C) is formed when Os3(CO)10(CH3CN)2 reacts with the subject alkynes in the presence of para-H2, but does not react with para-hydrogen. An unstable α-β-unsatu...

Bimetallic PtAu cluster-derived catalysts for the selective catalytic reduction of NO by propylene

The selective catalytic reduction of nitric oxide by propylene in the presence of excess oxygen has been investigated over a series of silica supported Pt and PtAu catalysts. Cluster-derived catalysts were prepared by wet impregnation using a Pt 2Au 4(CC tBu) 8 organometallic cluster precursor, and compared to catalysts obtained by incipient wetness impregnation using individual Pt and Au salts. The addition of Au by co-impregnation resulted only to a small shift (20–25 °C) in the light-off of propylene towards higher temperatures. A markedly different catalytic behavior was observed in the case of cluster-derived catalysts, where a 150 °C delay was observed both in the temperature of maximum NO reduction and the light-off of propylene in the presence and in the absence of NO. Most importantly, the selectivity towards N 2 increased by 50% compared to the monometallic Pt catalysts. The results of characterization studies indicate that the monometallic Pt/SiO 2 and the co-impregnated PtAu/SiO 2 samples have similar metal particle sizes. A more narrow particle size distribution was observed with the cluster-derived bimetallic sample.

Photochemical Generation of High Spin Clusters in Solution: (Cyclopentadienyl−Vanadium)mOn

Organometallic clusters containing oxygen atoms, (CpV)mOn (Cp = C5H5), are generated by photochemical reaction of CpV(CO)4 in CH2Cl2 solution with control of oxygen concentration. Mass spectra of single batch reactions exhibit strong signals assigned to low mass oxide clusters: (CpV)4O4, (CpV)5O6, and (CpV)6On (n = 6−8). Successive addition of reactant solution into the photochemical reaction vessel shows the addition of (CpV)m‘ to the low mass oxide clusters, producing (CpV)mOn (m ≫ n = 4−7). The magnetic susceptibility (χg) of the mixture of the former low mass products shows antiferromagnetic behavior, while that of the latter high mass products is as high as 4.6 × 10-4 cm3 g-1 at 10 K. The additional part due to high mass products behaves ferromagnetically at temperatures higher than 70 K.

Self-assembly of organometallic clusters onto the surface of gold

We report the preparation and characterization of thin films generated via the solution-phase self-assembly of organometallic chalcogen-containing cluster compounds onto the surface of gold. The following anionic complexes were used as thin film precursors: [Fe 3(CO) 9E] 2− and [HFe 3(CO) 9E] −, where E=S, Se, and Te. The films were prepared by adsorption from organic solvents (i.e. methanol, acetonitrile, acetone, and dicholoromethane) onto evaporated gold and were characterized by ellipsometry, polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS), X-ray diffraction (XRD), atomic force microscopy (AFM), quartz crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS). The data demonstrate that the clusters strongly attach to gold and that the films most likely exist as bilayers rather than monolayers.

Molecular Bioengineering of Multifuctional Markers for Energy Filtering Transmission Electron Microscopy (EFTEM) Correlative with Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI)

Abstract Molecular immunolabeling allows us to recognize location of molecules within complex biomolecular assemblies, cells, and organs. This technology helps us to facilitate correlations of the data available from biochemistry, molecular biology, pathology, and molecular imaging laboratories concerned with the gene expression as well as location and functions of its products. in this sense, molecular imaging serves as an integrative factor for life sciences endeavors (Albrecht et al. 1992, Bazett-Jones et al. 1996, Hainfeld and Powell 2000, Malecki et al. 1998, Robinson et al. 2000, Malecki 2000). Nevertheless, the essential requirement for pursuit of those projects is availability of molecular markers, which are detectable with various imaging instruments (Malecki 1996). Correlations between positron emission tomography (PET) providing metabolic information, magnetic resonance imaging (MRI) delineating precise anatomical location, and energy filtering transmission electron microscopy (EFTEM) expanding insights into the molecular level are particularly powerful. We have designed three main strategies for pursuit of this project: (a) expression of fusion proteins containing amplified metal binding sites (Malecki et al. 1998), (b) expression of recombinant single chain variable fragment (scFv) antibodies containing elemental recipient (Malecki et al. 2000), and (c) covalent coupling of IgG and Fab with organometallic clusters (Malecki 1996). Herewith, we report the results obtained through imaging of organometallic clusters inserted into the recombinant single chain variable fragment (scFv) antibodies.

47-Electron organometallic clusters derived by chemical and electrochemical oxidation of trihydrido(alkylidyne)triruthenium clusters: II. Disproportionation mechanism for decomposition

The decomposition of 47-electron clusters, generated by chemical or electrochemical oxidations of 48-electron H 3Ru 3(μ 3-CX)(CO) 9− n L n (X=OMe; L=PPh 3; n=0–3: X=OMe, SEt; L=dppm; L=PPh 3; n=3: X=SEt, NMeBz; L=PR 3, SbPh 3; n=2,3) occurs by disproportionation back to the 48-electron precursor and very unstable 46-electron species. Both 47/48- and 46/47-e redox potentials display similar ligand additivity trends, which are correlated with HOMO energies determined by Fenske–Hall MO calculations. Decomposition of [H 3Ru 3(μ 3-COMe)(CO) 6(PPh 3) 3] 1+ in the presence of added PPh 3 forms 48-e H 3Ru 3(μ 3-COMe)(CO) 6(PPh 3) 3, 46-e [H 3Ru 3(CO) 7(PPh 3) 3] 1+, and [MePPh 3] 1+; the rate law is second order with respect to concentration of the 47-e cluster and displays a small dependence on PPh 3 concentration. Decompositions of [H 3Ru 3(μ 3-COMe)(CO) 7(PPh 3) 2] 1+, [H 3Ru 3(μ 3-CSEt)(CO) 7(dppm)] 1+, and [H 3Ru 3(μ 3-CSEt)(CO) 6(PPh 3) 3] 1+ are also second order, although only the 48-e product could be characterized. The mechanism is proposed to involve rate-limiting outer-sphere electron transfer, the slow rate of disproportionation is a consequence of the fact that the reaction involves transfer of an electron from one half-filled bonding orbital to another half-filled bonding orbital, thus requiring considerable reorganization energy. Electrochemical studies of the 2-e oxidations of H 3Ru 3(μ 3-COMe)(CO) 9− n (PPh 3) n , n=0 and 1, indicate that the initial 46-e cluster rearranges very rapidly to a new 46-e species, which decomposes rapidly to electrochemically inactive products.

NMR, IR, Mössbauer and quantum chemical investigations of metalloporphyrins and metalloproteins

We review contributions made towards the elucidation of CO and O2binding geometries in respiratory proteins. Nuclear magnetic resonance, infrared spectroscopy, Mössbauer spectroscopy, X-ray crystallography and quantum chemistry have all been used to investigate the Fe –ligand interactions. Early experimental results showed linear correlations between17O chemical shifts and the infrared stretching frequency (νCO) of the CO ligand in carbonmonoxyheme proteins and between the17O chemical shift and the13CO shift. These correlations led to early theoretical investigations of the vibrational frequency of carbon monoxide and of the13C and17O NMR chemical shifts in the presence of uniform and non-uniform electric fields. Early success in modeling these spectroscopic observables then led to the use of computational methods, in conjunction with experiment, to evaluate ligand-binding geometries in heme proteins. Density functional theory results are described which predict57Fe chemical shifts and Mössbauer electric field gradient tensors,17O NMR isotropic chemical shifts, chemical shift tensors and nuclear quadrupole coupling constants (e2qQ/h) as well as13C isotropic chemical shifts and chemical shift tensors in organometallic clusters, heme model metalloporphyrins and in metalloproteins. A principal result is that CO in most heme proteins has an essentially linear and untilted geometry (τ = 4 °, β = 7 °) which is in extremely good agreement with a recently published X-ray synchrotron structure. CO / O2discrimination is thus attributable to polar interactions with the distal histidine residue, rather than major Fe–C–O geometric distortions.

A soft-landing experiment on organometallic cluster ions: infrared spectroscopy of V(benzene) 2 in Ar matrix

Vanadium (V)–benzene cluster ions, produced by laser ablation with reaction toward benzene vapor, were size-selected and deposited into a low-temperature Ar matrix. Infrared spectrum of V 1(benzene) 2 in the Ar matrix was measured after one-hour deposition with the deposition energy of 20 eV. The spectrum was in agreement with both the reported spectrum and our theoretical calculations, showing that (1) V 1(benzene) 2, prepared in the gas-phase reaction, takes a sandwich structure and that (2) the ions were soft-landed onto the Ar matrix and were neutralized by charge transfer from a metal substrate without fragmentation.

DRIFTS studies of carbon monoxide coverage on highly dispersed bimetallic Pt-Cu and Pt-Au catalysts

Silica supported platinum-gold and platinum-copper catalysts prepared from organometallic cluster precursors were characterized with diffuse reflectance Fourier-transform spectroscopy (DRIFTS) of adsorbed CO. Because of the effects that dipole coupling of adsorbed carbon monoxide molecules can have on the infrared spectrum, coverage studies were employed to evaluate the interactions between CO and the catalyst surfaces. DRIFTS spectra of the catalysts prepared from bimetallic molecular cluster precursors showed significantly lower CO stretching frequencies relative to a traditionally prepared platinum catalyst. The lowering of the CO stretching frequency may be the result of the formation of unique alloys and particle morphologies. In the case of the catalyst prepared from the platinum-copper cluster, two peaks were identified in the PtCO stretching region, one of which is postulated to be a bridging or semi-bridging mode between Pt and Cu. Infrared spectroscopy results are also discussed in relation to kinetic data from the n-hexane conversion reaction. Differences in catalyst activities and selectivities are concluded to be primarily due to geometric (i.e. structural or morphological) effects.

Reactions of nickelocene with an Ru5 cluster: crystal structures of two nickel–ruthenium clusters containing C2 ligands

Reactions of nickelocene with Ru5(μ5-C2)(μ-SMe)2(μ-PPh2)2(CO)11 have given NiRu5(μ6-C2)(μ-SMe)2(μ-PPh2)2(CO)9Cp2 and Ni2Ru4(μ6-C2)(μ-SMe)2(μ-PPh2)2(CO)8Cp2 whose molecular structures have been determined. The NiRu5 cluster is related to other heterometallic clusters containing FeRu5, Ru6 or Co2Ru5 cores which contain two edge-fused squares supporting the C2 ligand, one carbon occupying the centre of each square face while retaining the C–C bond. However, there is no formal M–M interaction along the shared edge. Substitution of CO groups by Cp on one Ru atom has occurred. The structure of the Ni2Ru4 cluster is similar, with the six-membered ring having the boat conformation. The C2 ligand takes up two disordered (1∶1) positions, either parallel or perpendicular to the non-bonding Ni ⋯ Ni vector. Extended Huckel and density functional calculations have been carried out on Ni2Ru4(μ6-C2)(μ-SMe)2(μ-PPh2)2(CO)8Cp2 to rationalise these two observed coordination modes of the C2 unit to the metal framework. Results suggest that the two arrangements are isoenergetic and that the M–C bonding follows the Dewar–Chatt–Duncanson model as previously found for related C2-containing polynuclear organometallic clusters.

M4X4 Structures in Transition Metal Chemistry: Cubane-like or Planar? A DFT Study of Some Clusters Containing the M4X4 Core (M = Ti, V, Mo; X = N, P, As)

DFT calculations have been carried out on the organometallic clusters [(η-C5H5)TiN]4 and [Cl3MoN]4 with the aim of comparing the energies and the electronic structures of the cubane and planar forms for these two clusters. Calculations indicate for the titanium cluster that the cubane conformation is much more stable than the structure in which the four metals and the four nitrogens are in the same plane, whereas the square planar structure is preferred for the molybdenum complex. The octahedral coordination of the metal in the cubane-like form implies an important reorganization of the [Cl3MoN] unit. The high cost of this reorganization explains the relative stability of the square planar conformation in that case. Metal−metal interactions have been characterized in the vanadium cubanes [(η-C5H5)V(μ3-X)]4, X = N, P, and As. The distortion of the cage observed in some cubanes is discussed in relation to the metal−metal bonding interactions evidenced in these clusters.

Characterization of organometallic coordinative cluster compounds of silver by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Characterization of organometallic coordinative cluster compounds of silver by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Characterization of organometallic coordinative cluster compounds of silver by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was successfully applied to characterize the organosilver coordinative cluster compounds, silver phenylacetylide and three silver thiolates, namely, silver tertiary butylthiolate, silver 2,6-dimethylbenzenethiolate, and silver 2, 6-dichlorobenzenethiolate. Samples and dithranol matrix were finely dispersed in 1:1 tetrahydrofuran (THF)/chloroform (CHCl(3)) mixed solvent. In most cases the monomer units remained intact during ionization, and the oligomeric molecular ions were produced through silver cationization, with a general molecular ion formula [nM + Ag](+). This was further verified by the relative abundances of the isotopic peaks within the molecular ion clusters, which were in close agreement with those theoretically calculated for nM cationized with one silver ion. In the case of silver 2, 6-dichlorobenzenethiolate, in addition to the dominant [nM + Ag](+) peaks, weak peaks corresponding to the successive losses of hydrogen chloride molecules were observed. Copyright 2000 John Wiley & Sons, Ltd.

Hydrogen bonds and other intermolecular interactions in organometallic crystals †

Organometallic compounds have been studied with X-ray crystallography from their very discovery. Yet structural organometallic chemists were almost exclusively concerned with the molecular structure and stereochemistry of organometallic compounds and clusters rather than with their crystal structures and packing characteristics. The growing importance of crystal engineering and supramolecular chemistry, however, led to interest in the nature of the interactions that bind organometallic molecules into crystals. In part, these interactions are similar to those found in purely organic crystals because the peripheries of these molecules often contain organic residues. Yet molecular features peculiar to organometallic compounds also do lead to distinctive supramolecular characteristics. Most notable among these intermolecular interactions are hydrogen bonds. Organometallic compounds contain a wealth and diversity of hydrogen bonds that are without counterpart in the organic world. These include C–H⋯O bonds to M–CO acceptors, and hydrogen bonds wherein the metal atom itself acts as a donor or as an acceptor. Even more exotic is the dihydrogen bond M1–H⋯H–M2. Despite this variety, all these weak interactions have properties that resemble those of the more familiar hydrogen bonds such as O–H⋯O, N–H⋯O, O–H⋯N and N–H⋯N. Other interactions that are distinctive to organometallic compounds are the agostic interaction to electron deficient metals (C–H)⋯M and the aurophilic interaction Au⋯Au. The Cambridge Structural Database (CSD) is an essential tool in the analysis of weak intermolecular interactions. Since the number of organometallic crystal structures in the CSD is very large, the weakest of intermolecular interactions may be studied with ever-increasing degrees of reliability. Through such analysis one is able to obtain a more complete idea of organometallic crystal architecture. Crystal engineering must pass through the stage of analysis before crystal synthesis can be attempted and organometallic crystal engineering is still in its infancy. However, the progress made so far in understanding the nature of intermolecular interactions in these crystals indicates that one may expect rapid progress in the engineering of organometallic crystals with desired structures and properties.

A Novel Network Structure of Organometallic Clusters in the Gas Phase

Synthesis of organometallic compounds in gas phase presents a novel guideline to preparative chemists because they can be prepared without solvent and oxidation in air. Especially, the application of the laser vaporization to the gas-phase synthesis of organometallic compounds enables us to prepare the constituents in considerable density in a short time because there are no interfering effects of solvents, aggregation phenomena, and counter ions. This new approach should open up an entirely different aspect of organometallic chemistry and physics, which can be studied quite nicely in the gas phase, and indeed several groups independently have succeeded in the synthesis of novel organometallic complexes.1-7 The technique used to produce and detect the gas- phase organometallic clusters involves a beam source with laser vaporization of metal rods and time-of-flight mass spectrometry whose distinct ability was well-demonstrated in the discovery of C60 8 and metallo-carbohedrene,9,10 a so-called met-car.

Generation and electronic properties of lanthanide–cyclooctatetraene organometallic clusters in gas phase

Organometallic clusters of lanthanide (Ln = Nd, Er, Eu, and Yb) and 1,3,5,7-cyclooctatetraene (C8H8) were produced by a combination of laser vaporization and molecular beam methods. In the mass spectra of [Lu n (C8H8) m ], compositions of m = n + 1 were magic numbers. From mass spectrometry, photoionization spectroscopy, and photoelectron spectroscopy, we have concluded that these magic-numbered clusters take multiple-decker sandwich structures in which Ln atoms and C8H8 molecules are alternatedly piled up. These sandwich clusters are formed through ionic bonds composed of multiply charged cations [Ln k+ (k = 2 and 3)] and multiply charged anions [C8H 8 h− (h = 1, 1.5, and 2)].

Synthesis and Structural Characterization of Novel Organolanthanide Clusters Containing Amido and Imido Groups

Treatment of Me2Si(C9H7)(C2B10H11) with 4 equiv of NaNH2 in THF, followed by reaction with 1 equiv of LnCl3 at room temperature, afforded [{(η5-μ2-C9H6SiMe2NH)Ln}2(μ3-Cl)(THF)]2(μ4-NH)·nOC4H8 (n = 1, Ln = Gd (Ia), Er (Ib); n = 0, Ln = Dy (Ic)), which represent not only the first examples of organometallic clusters containing a central μ4-imido group but also the first organolanthanide indenyl clusters to be reported. Another type of tetranuclear cluster, [{(η5-C9H6SiMe2)2N}(μ2-NH2)Ln2(THF)2]2(μ3-Cl)2(μ2-Cl)2·THF (Ln = Gd (IIa), Y (IIb)), was obtained if the above reactions were carried out at reflux temperature. This type of cluster can also be prepared by refluxing cluster type I in THF in the presence of NaCl. Treatment of Me2Si(C9H7)(C2B10H11) with 8 equiv of NaNH2 in THF, followed by reaction with 1 equiv of LnCl3 at room temperature, gave the trinuclear clusters [(η5-C9H6SiMe2)2N][μ2,μ2-Me2Si(NH)2](η5-μ2-C9H6SiMe2NH)(μ2-Cl)2Ln3(THF)3 (Ln = Gd (IIIa), Er (IIIb)). These results indicate that NaNH2 serv...

Pyramidal Structures of Lanthanide−C60 Clusters (Lnn(C60)m: Ln = Eu and Ho)

Novel lanthanide organometallic clusters, Lnn(C60)m, consisting of lanthanide atoms (Ln; Ln = Eu and Ho) and C60 molecules were produced in gas phase by a two-laser vaporization method. The Lnn(C60)m clusters were produced predominantly at compositions of (n, m) = (n, n + 3) [n = 1−4]. These stoichiometries showed no chemisorption reactivity toward CCl4 and O2 reactants. The cluster having (1, 4) composition is proposed to form a tetrahedral structure, in which a Ln atom is surrounded by four C60 molecules. In larger clusters with (n, n + 3) composition, each Ln atom is found in a local (1, 4) group. Together with the results of sequential chemisorption of Cl atoms on cluster cations, photoelectron spectroscopy of cluster anions leads us to conclude that Ln1(C60)m clusters are charge-transfer complexes expressed as Ln1x+(C60)mx-, and that Eu and Ho atoms exist as Eu2+ and Ho3+ ions, respectively.

Preparation and Characterization of Supported Bimetallic Pt–Au Particle Catalysts from Molecular Cluster and Chloride Salt Precursors

New silica-supported bimetallic Pt–Au catalysts were prepared using an organometallic Pt–Au cluster precursor and compared with Pt and Pt–Au catalysts prepared by the incipient wetness impregnation of chloride salts. The supported catalyst precursors were calcined and reduced under identical conditions and the resulting catalysts were characterized with transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), CO chemisorption, and diffuse reflectance infrared Fourier Transform spectroscopy (DRIFTS). Temperature-programmed reduction experiments were also performed on the freshly supported precursors and after calcination. The bimetallic cluster precursor yielded catalysts with small (d≈2.5 nm), uniform particles that have high Pt dispersion. EDS, CO chemisorption, and DRIFTS of adsorbed CO experiments gave strong evidence that these particles are bimetallic. Using the organometallic cluster precursor also caused a significant red shift (12 cm−1) in the stretching frequency of adsorbed carbon monoxide relative to the traditional Pt catalyst. Catalytic performance was evaluated with the hexane conversion reaction. Results showed that the cluster-derived catalysts enhance the production of light hydrocarbons and decrease the rate of skeletal reforming reactions. Despite the enhancement of C–C bond fission reactions, catalysts prepared from the organometallic precursor had greatly enhancing resistance to deactivation. In contrast, the coimpregnation of Au with Pt from chloride salts yielded catalysts with little or no interaction between the two metals. For these catalysts, light hydrocarbon production decreased yet skeletal rearrangements were not measurably affected.