Transition Metal Cluster Ions Research Articles

Photoelectron spectroscopy of size-selected cluster ions using synchrotron radiation

A new experimental setup for photoelectron spectroscopy of size-selected cluster ions using synchrotron VUV radiation as generated by the Swiss Light Source is presented. An intense positively charged cluster ion beam is produced in a high-intensity magnetron sputter source. The clusters are subsequently mass selected in a sector magnet. To maximize the residence time of the cluster ions in the ionization region of the velocity map imaging spectrometer, the cluster ion beam is decelerated where it crosses the light beam. First experiments on (MoO3)n+ (n = 69 and 59) cluster cations show that the approach is capable of delivering photoelectron spectra of size-selected transition metal cluster ions.

Faraday Rotation Caused by Mixed Valence Centers in Magnetic Crystals

The peculiarities of the Faraday rotation in the imperfect garnet-type crystals for which the lattice irregularities are represented by the mixed valence clusters of transition metal ions are analyzed. The model takes into account the cubic and low symmetry crystal fields acting on the metal ions and migration of the “extra” hole. The electric dipole transitions in these types of clusters with migrating hole coupled to the spin core through the double exchange mechanism are shown to lead to a significant magnetooptical activity in the visible range of spectrum. The intensity of these transitions can be comparable or higher than those for the magnetic dipole ones in the same range of frequencies.

ChemInform Abstract: Generation and Reactivity of State-Selected Atomic and Size-Selected Transition Metal Cluster Ions

ChemInform Abstract: Generation and Reactivity of State-Selected Atomic and Size-Selected Transition Metal Cluster Ions

Magnetooptical activity of spinel type crystals with complex mixed-valence lattice irregularities

In this Letter we analyze the peculiarities of the Faraday rotation in the imperfect spinel type crystals for which the lattice irregularities are represented by the mixed valence clusters of transition metal ions. A such kind of complex system with the electronic configuration d 5 ( t 2 g 3 e g 2 ) − d 5 ( t 2 g 3 e g 2 ) − d 4 ( t 2 g 2 e g 2 ) (for example, Mn 2 + Mn 2 + Mn 3 + ) is considered in detail. The model takes into account the cubic and low symmetry crystal fields acting on the metal ions, migration of the “extra” hole as well as the orientational degeneracy (hidden optical anisotropy). The electric dipole transitions in these types of clusters with migrating hole coupled to the spin core through the double exchange mechanism are shown to lead to a significant magnetooptical activity in the visible range of spectrum. The intensity of these transitions can be comparable or higher than those for the magnetic dipole ones in the same range of frequencies. The electric dipole mechanism of the magnetooptical effects manifests itself in a highly anisotropic character of the spectra.

Mass Spectroscopy of Chemical Reaction of 3d Metal Clusters Involved in Chemical Vapor Deposition Synthesis of Carbon Nanotubes

The chemical reactions of transition metal clusters in the gas phase have aroused considerable scientific interest and are also of critical scientific importance. For example, these reactions are involved in the synthesis of single-walled carbon nanotubes, which are considered ideal materials because of their outstanding properties. Alcohol catalytic chemical vapor deposition (ACCVD) is one of the best synthetic processes for carbon nanotubes (CNTs); however, even the initial growth mechanism is still unclear, unlike those of other synthetic processes. In this study, we used a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer to determine the initial reactions of transition metal cluster ions (iron, cobalt, and nickel) that are typically adopted in the alcohol CVD process. Metal clusters with approximately 10–25 atoms each, generated by a pulsed laser ablation system in a supersonic-expansion cluster beam source, were directly carried into the FT-ICR cell. Subsequently, ethanol was introduced into the ICR cell. We observed two different results: one was simple chemisorption observed in the iron cluster and the other was dehydrogenated chemisorption observed in the nickel cluster; however, cobalt clusters exhibited both patterns, and a sequential reaction was observed. Furthermore, the dehydrogenation of ethanol on the cobalt cluster is fully described from isotope-labeled experiments.

Chemical Reactivity and Tendency of Fe, Co and Ni Clusters with Ethanol by Using FT-ICR Mass Spectrometer

Chemical reaction of transition metal cluster ions (Fe, Co, Ni) with ethanol was investigated by using the FT-ICR mass spectrometer. Metal clusters with 10-20 atoms were generated by a pulsed laser-vaporization supersonic-expansion cluster beam source directly connected to FT-ICR mass spectrometer. Observed reactions are simple chemisorptions of ethanol and dehydrogenated chemisorptions strongly depending on metal species and cluster size. The reaction of iron clusters show simple chemisorptions and the reaction of nickel clusters show dehydrogenated chemisorptions. However cobalt clusters show both reaction patterns. Thus the reaction patterns change according as periodic table. And the cluster sizes which show the maximum reaction rate also shified according as periodic table.

Anisotropic and antisymmetric double exchange in mixed-valence clusters

In the mixed-valence dn–dn+1 clusters of transition metal ions, taking the spin–orbit coupling into account in the Anderson–Hasegawa double exchange model results in anisotropic double exchange and antisymmetric double exchange. The anisotropic double exchange results in the zero-field splittings of the double exchange levels. These zero-field splittings are described by the the effective ZFS Hamiltonian, which is active between the states of different localization of the extra electron. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Anisotropic double exchange in mixed-valence dimeric clusters of transition metal ions

In the mixed-valence (MV) [dn–dn + 1] clusters of non-degenerate transition metal ions with the migration of the extra electron, taking the spin–orbit coupling into account in the double exchange (DE) model results in anisotropic double exchange interaction or anisotropic spin-dependent electron transfer which is described by the effective Hamiltonian HDEAN=∑α∑n=x,y,z[Antμ(Sˆ←α∗nτˆαβSˆ→β∗n)+Bntv(Sˆ←α∗nτˆαβSˆ→αn+Sˆ←βnτˆαβSˆ→β∗n)], τab is the one-electron DE operator. For the MV [d8–d9] cluster, the coefficients of the double exchange anisotropy Antμ, Bntv linearly depend on the DE parameters tμ and tv of the excited and ground cluster DE states. The one-center spin operators Sˆ←α∗n,Sˆ→β∗n(Sˆ→αn) act in the states of different localization. The anisotropic spin-transfer interaction HDEAN is active between the states of different localization of the extra electron. Anisotropic double exchange coupling results in the zero-field splitting (ZFS) of the high-spin DE levels E±0(S=3/2). This splitting is described by the effective ZFS HamiltonianHZFSt=DtTˆab[SZ2-S(S+1)/3]+EtTˆab(SX2-SY2), where Tˆab is the double exchange operator in the S representation. The ZFS parameters Dt and Et of the anisotropic DE origin are linearly proportional to the double exchange parameters tμ. In the MV clusters, the ZFS operator HZFSt acts between the S states of different localization and should be added to the standard ZFS Hamiltonian HZFS0=DS[SZ2-S(S+1)/3]+ES(SX2-SY2), which is active in the localized states. The anisotropic double exchange contributions to the ZFS have different sign for the E+0(S)andE-0(S) DE states: D[E±0(S)]=DS±Dt,E[E±0(S)]=ES±Et. The anisotropic DE contributions Dt, Et to the cluster ZFS parameters (DS ± Dt, ES ± Et) may be larger than the single-ion (Di,Ei) and anisotropic (pseudodipolar) exchange (Dpd, Epd) contributions.

Energetics of the manganese trimer and tetramer ions

The photodissociation processes of the manganese cluster ions Mnn+ (n=3 and 4) were investigated in the visible and near-infrared photon-energy ranges. The threshold energies were determined for the two-atom-loss channels by measurements of the spectra of the partial photodissociation cross sections. The binding energies of Mnn+ (n=3 and 4) were obtained by using these threshold energies and the known bond dissociation energy of Mn2+. The bond dissociation energies of Mn3+, D0(Mn2+⋯Mn), and Mn4+, D0(Mn3+⋯Mn), were determined to be 0.83±0.05 and 1.04±0.07 eV, respectively. Thus the binding energies (per atom) of Mn3+ and Mn4+ turned out to be 0.74±0.03 and 0.82±0.05 eV, respectively. These findings show that the interaction between manganese atoms is exceptionally weak, compared with other transition-metal cluster ions.

Reactions and thermochemistry of small transition metal cluster ions.

This review discusses the reactivities and thermodynamics of small-size-specific transition metal clusters and focuses on thermodynamic information, which has not been comprehensively discussed before. Because of this focus, guided-ion-beam mass spectrometry was used to acquire much of the data. The details of this technique and the associated data analysis methods are provided. Results on the stabilities of bare transition metal clusters are provided for neutral, cationic, and anionic species. Implications for the electronic and geometrical structures are discussed, as well as the extrapolation of these values to bulk phase behavior. Detailed results for reactions of transition metal clusters with D2 and the oxygen donors O2 and CO2 are reviewed. Available bond energies between size-specific clusters and one D atom and one and two O atoms are compiled, and their implications are evaluated and favorably compared with bulk phase analogs. Several additional thermodynamic studies of various cluster systems are also discussed.

Analysis of optical absorption spectra of transition metal cluster ions by the spin-polarized DV- Xα method

Optical absorption spectra of cobalt cluster ions, Con+, and vanadium cluster ions, Vn+, were analyzed by a theoretical calculation based on the spin-polarized DV-Xα method, and their electronic and geometric structures were obtained. Relative absorption cross section associated with each electronic transition was calculated; the calculation enables a qualitative comparison of calculated spectrum with a measured one not only in its transition energy but also in its intensity profile. This analysis shows that Co4+, Co3+, and V4+ have, respectively, a tetrahedral structure with a bond distance of 2.00A, an equilateral triangle with a bond distance of 2.30A, and a distorted tetrahedral structure with five bonds having a distance of 2.34 A and one of 2.89A. The differences in the population between majority and minority spins (spin-difference) evaluated from the electronic structure thus obtained were 2.0, 1.7, and zero per atom in Co3+, Co4+, and V4+, respectively. These spin differences indicate a ferromagnetic and an antiferromagnetic spin-coupling in the cobalt and vanadium cluster ions, respectively.

Electronic structure of paramagnetic clusters of transition metal ions. 3. Magnetic properties and scattered wave description of the electronic structure of the hexanuclear octahedral cluster [Fe6(μ3−S)8(PEt3)6] (BPh4)2

AbstractSpin‐polarized Xα–SW calculations of [Fe6(μ3−S)8(PH3)6]2+ as a model of the cluster [Fe6(μ3−S)8(PEt3)6] (BPh4)2 have been performed. The highest occupied energy levels are well separated from empty levels, and up to a maximum of eight electrons can be unpaired, giving a maximum spin state with S = 4. This electronic state is consistent with the magnetic data of [Fe6(μ3−S)8(PEt3)6](BPh 4)2, which have been interpreted using the Heisenberg–Dirac–Van Vleck exchange spin Hamiltonian. The S = 4 state arises from the magnetic coupling between five low‐spin (Si = 1/2) and one intermediate‐spin (S = 3/2) iron(III) center. © 1994 John Wiley & Sons, Inc.

Vibronic interaction in multielectronic mixed-valence trimeric clusters

The problem of vibronic interaction in multielectronic trimeric clusters of transition metal ions is considered. The dynamic vibronic problems are solved numerically for the d1-d1-d0 and d1-d1-d2 trimers taking into account both the electron transfer (double exchange) and the isotropic (Heisenberg type) exchange interaction. For both types of system (i.e. d1-d1-d0 and d1-d1-d2) the joint action of the electron transfer and vibronic interaction is shown to lead to the (A1 + E) ⊗ e and (A2 + E) ⊗ e pseudo Jahn-Teller problems. For the d1-d1-d2 clusters the more complicated (A1 + A2 + E + E) ⊗ e dynamic problem also appears. The magnetic properties of the above mentioned systems are discussed in detail. Some comments concerning spin models of double exchange are given in connection with the problem of vibronic interaction in mixed-valence clusters. As distinguished from the microscopic quantum-mechanical approach the conventional spin-model is shown to meet difficulties in the solving of the vibronic problem of mixed-valence trimers (and systems of higher nuclearity as well). All the vibronic matrices in the symmetry-adopted bases are given in the Appendix for the d1-d1-d2-, d2-d2-d3-, d3-d3-d2- and d3-d3-d4-mixed-valence trimers. These matrices are necessary for the calculations of the vibronic spectra of systems of such type.

Electronic structure of paramagnetic clusters of transition metal ions. 2. Crystal and molecular structure, single crystal EPR spectra, and magnetic properties of [Co6(.mu.3-S)8(PEt3)6](PF6)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectronic structure of paramagnetic clusters of transition metal ions. 2. Crystal and molecular structure, single crystal EPR spectra, and magnetic properties of [Co6(.mu.3-S)8(PEt3)6](PF6)Alessandro Bencini, Carlo A. Ghilardi, Annabella Orlandini, Stefano Midollini, and Claudia ZanchiniCite this: J. Am. Chem. Soc. 1992, 114, 25, 9898–9908Publication Date (Print):December 1, 1992Publication History Published online1 May 2002Published inissue 1 December 1992https://doi.org/10.1021/ja00051a023RIGHTS & PERMISSIONSArticle Views188Altmetric-Citations25LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Thermal bimolecular reactions of size selected transition metal cluster ions: Nb +n + O 2, n = 1–6

Niobium cluster ions, Nb + n , are generated using a new laser desorption source. This source, floated at 5 kV, is coupled to a high resolution reverse geometry mas spectrometer. Mass selected cluster ions exiting the mass spectrometer are decelerated to several electronvolts and spatially focused on a small hole in the entrance plate to a high pressure (0–7 Torr), variable temperature (80–600K) drift reactor. The cluster ions gently drift through this 4 cm long cell under the influence of small electric fields. A helium buffer gas is used to thermalize the ions. Trace amounts of O 2 are added for the reaction studies. Ions exiting the drift reactor are analyzed using a quadrupole mass filter and ion counting techniques. The quadrupole mass filter has an upper mass range of about 600 dalton, limiting the current maximum cluster size to n = 6. All reactions of Nb + n with O 2 are found to be fast, proceeding at 40 ± 10% of the collision rate. For n = 2–6, the major (90%) product results from loss of NbO from the Nb + n · O 2 collision complex. For n = 3–6, other (small) competing channels include loss of NbO 2 and Nb atoms from the collision complex. Fast sequential reactions of the reaction products with O 2 are observed. An analysis of the arrival time distribution of Nb + at the detector indicates laser desorption forms ≈ 80% ground state (4d 4, 5D) and 20% excited state (4d 3 5s 1, 5F). Collisional deactivation by He occurs at a rate constant ⪡ 1 × 10 −15 cm 3s −1.

Heteronuclear diatomic transition-metal cluster ions in the gas phase: Reactivity and thermochemistry of AgFe+

The gas-phase chemistry of AgFe+ was studied by using Fourier transform ion cyclotron resonance mass spectrometry. AgFe+ is unreactive with alkanes but reacts with cyclic and linear (C4–C8) alkenes. The primary reactions are dominated by dehydrogenation and condensation. In addition, cluster splitting is observed in the reaction of AgFe+ with benzene. Secondary reactions generally involve cluster splitting with the loss of Ag, although AgFeC5H 6 + is observed to dehydrogenate cyclopentene to yield AgFeC10H 12 + . Ion-molecule reactions, collision-induced dissociation, and photodissociation experiments were used to determine the bond energiesD°(Fe+−Ag)=53±7 kcal/mol andD°(Ag+−Fe)=46±7 kcal/mol. These values in turn were used to calculateΔH f (AgFe+)=296±7 kcal/mol andIP(AgFe)=6.5±0.3 eV. Related chemical and physical properties of CuFe+ are presented for comparison.

Charge Ordering of Multielectronic Clusters in Mixed‐Valence Molecular Crystals

AbstractMixed valence molecular crystals consisting of multielectronic clusters of transition metal ions of the type of d2–d3 are considered. A theory of charge ordering in these crystals is developed. The conditions for the occurence of one, two, or three phase transitions are eludicated. The peculiarities of the temperature behaviour of the magnetic moment are investigated.

Charge Transfer Bands of Mixed Valence Molecular Crystals

Abstract The electron-vibrational (vibronic) bands of light absorption by mixed valence molecular crystals containing clusters of transition metal ions in different states of oxidation as the structural units of lattice are considered. The absorption band shape calculation in different phase states is performed in the semiclassical limit for crystals consisting of trielectronic clusters of transition metals of the type of d1-d2. The band shape differs from the Gaussian and closely depends on the double-exchange and Heisenberg-type exchange parameters and on the temperature dependence of the average dipole moment playing the role of the order parameter.

ChemInform Abstract: Heteronuclear Diatomic Transition‐Metal Cluster Ions in the Gas Phase: Reactions of ScFe+ with Hydrocarbons.

AbstractFourier transform mass spectrometry shows that the title cluster ion is reactive with various alkenes but unreactive with alkanes.

Heteronuclear diatomic transition-metal cluster ions in the gas phase: reactions of ScFe+ with hydrocarbons

Heteronuclear diatomic transition-metal cluster ions in the gas phase: reactions of ScFe+ with hydrocarbons