Neutral Transition Metal Atoms Research Articles

The metallo-formate anions, M(CO2)-, M = Ni, Pd, Pt, formed by electron-induced CO2 activation.

The metallo-formate anions, M(CO2)-, M = Ni, Pd, and Pt, were formed by electron-induced CO2 activation. They were generated by laser vaporization and characterized by a combination of mass spectrometry, anion photoelectron spectroscopy, and theoretical calculations. While neutral transition metal atoms are normally unable to activate CO2, the addition of an excess electron to these systems led to the formation of chemisorbed anionic complexes. These are covalently bound, formate-like anions, in which their CO2 moieties are significantly reduced. In addition, we also found evidence for an unexpectedly attractive interaction between neutral Pd atoms and CO2.

Endohedral and Exohedral Complexes of T8-Polyhedral Oligomeric Silsesquioxane (POSS) with Transition Metal Atoms and Ions

The equilibrium geometries of the exohedral and endohedral complexes of the polyhedral oligomeric silsesquioxane (POSS) cage (HSiO3/2)8 containing the transition metal atoms or ions Sc0,+, Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu0,+, Zn0,+, Mo0,+, W0,+, Ru0,+, Os0,+ have been investigated at the B3LYP/LanL2DZ levels. All these species form endohedral complexes with the T8-POSS cage except Sc0,+, Mo0, and W0,+. The Mo0 and W0,+ species as well as Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu+, Zn+, Ru0,+, Os0 form stable exohedral complexes. Geometries, electronic properties and ionization potentials were computed. The Si−O and Si−H bond lengths in the cationic endohedral complexes are shorter than in the corresponding complexes of neutral transition metal atoms. The zero-point corrected inclusion energies of the endohedral species X@(SiHO3/2)8 (X = Fe+, Co+, Ni+, Cu+, Os+) are all negative, suggesting that these complexes are more stable than their isolated components. All exohedral complexes have energies that are lower than their corresponding endohedral analogs. Transition metal atom encapsulation raised the HOMO and lowered the LUMO energies, reducing the HOMO−LUMO gaps of every complex compared to that of the pure cage. The HOMO−LUMO gap of the empty cage is 8.1 eV while the endohedral complexes exhibit gaps between 1.2 and 4.96 eV. Insertion of Cr, Fe, Co, Ni, Cu, or Zn into the POSS cage is more favorable in water than in the gas phase. However, insertion of Co+, Ni+, Cu+, or Zn+ into the POSS cage is less favorable in water than in the gas phase. Overall, both the neutral and ionic endohedral transition metal complexes, X@(SiHO3/2)10, (X = Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu0,+, Zn0,+, Ru0,+, Os0,+) appear to be viable synthetic targets.

Reactions of Neutral Transition Metal Atoms with Small Molecules in the Gas Phase

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Competition between C-C and C-H insertion in prototype transition metal-hydrocarbon reactions.

The competition between C-C and C-H insertion in model transition-metal reactions with cyclopropane and propene (C3H6) was studied as a function of total energy. Insertion of neutral transition metal atoms M (= Y, Zr, Nb, and Mo*) into the C-C bonds of cyclopropane led to formation of MCH2 + C2H4, whereas C-H insertion produced MC3H4 + H2. The measured product branching ratios verify the relative potential energy barrier heights for C-C and C-H insertion predicted by ab initio calculations.

Excited state kinetics of neutral transition metal atoms by stimulated emission pumping: V*(3d44s,a4D)+hydrocarbons

Stimulated emission pumping (SEP) by two tunable, ns dye lasers selectively creates metastable V*(3d44s,a4DJ*) excited states near 8500 cm−1 in a fast flow reactor with 1.2 Torr He buffer gas at 300 K. Subsequent collisions with He equilibrate the spin-orbit levels J*=1/2–7/2 on a time scale of 1 μs but do not quench the 3d44s, a4D multiplet on a time scale of at least 50 μs. A third probe laser placed 5 mm downstream of the SEP lasers monitors the V* population at fixed reaction time t=40 μs. The exponential decay of V* vs calibrated hydrocarbon flow yields total removal rate constants that include both chemical reaction and electronic quenching of the V* excited state. Coupling of diffusion with reaction/quenching evidently does not cause the slight positive curvature observed in the kinetics plots. We demonstrate this by solving two simplified models of the reacting, diffusing, flowing gas for our experimental geometry, with SEP and probe laser beams transverse to the flow tube axis. Instead, the curvature is probably caused by the delayed, collisional cascade of a small population of higher excited states into the V* state. Ethylene removes the V* state on essentially every hard-spheres collision. The alkanes CH4, C2H6, and C3H8 remove V* on one in 75, one in 25, and one in 12 collisions. This is remarkably inefficient reaction/quenching, given that the low-spin 3d44s state is ideally configured for CH or CC bond insertion in alkanes. We interpret these new results and earlier work of Honma and co-workers on the sextet 3d44s excited state in terms of avoided intersections between repulsive and attractive diabatic potential surfaces (conserving electron spin and configuration).

Gas Phase Kinetics of Neutral Transition Metal Atoms: Reactions of Hf, Ta, Ir, Pt, and Au with Alkanes and Alkenes

The chemical kinetics of the ground-state, neutral transition metal atoms Hf, Ta, Ir, Pt, and Au with alkanes and alkenes is surveyed. Laser-induced fluorescence measures effective bimolecular rate constants at 300 K in 0.5−1.1 Torr of He buffer gas. Pt(5d96s1) is thus far the only ground-state neutral atom in the entire transition metal block that reacts with methane. It also reacts rapidly with linear alkanes, cyclopropane, and the alkenes. Au(5d106s1) reacts only with the largest alkenes studied, and then very slowly. In spite of their 6s2 ground-state configurations, Hf(5d26s2), Ta(5d36s2), and Ir(5d76s2) react rapidly with alkenes including ethene; these atoms do not react with methane and the linear alkanes. An attempt is made to interpret the pattern of reactivity in terms of simple chemical bonding concepts, including electron configuration and spin, guided by earlier extensive electronic structure calculations for the 4d series. It appears that the lanthanide contraction of the 6s orbital strongl...

The Importance of Electron Transfer Mechanism in Reactions of Neutral Transition Metal Atoms

Reaction kinetics of ground, Ti(a3F) and V(a4F), and excited, Ti(a5F) and V(a6D), states atoms with some simple molecules have been studied by a discharge‐flow tube technique. Laser‐induced fluorescence (LIF) was used to determine the concentration of the metal atoms as a function of the flow rate of the reactant molecule to obtain effective bimolecular rate constants. The rate constants of reactions with OX (X = O, N, N2) and H2S show strong inverse correlation with effective ionization potentials (I.P.‐Eel, where I.P. and Eel are ionization potential and electronic energy of metal atom) of the metal atoms. This result suggests that the electron transfer mechanism plays an important role in these reactions. The large rate constants for electronic excited states can be explained by the crossing between ionic and flat neutral potential energy surfaces. The inefficient reaction rates measured for ground states can be explained by the repulsive nature of 4s2 configuration which can result in a potential barrier.

Gas-phase kinetics of neutral transition metal atoms: reactions of yttrium through molybdenum with alkanes and alkenes at 300 K

We survey the reactivity of ground-state, neutral transition metal atoms from the left-hand side of the 4d series (Y through Mo) with eight alkanes and alkenes. Effective bimolecular rate constants are measured in 0.5-0.8 Torr of He in a fast flow reactor at 300 K with laser-induced fluorescence detection. None of the four ground-state metal atoms reacts with linear alkanes. Mo reacts slowly and Y, Zr, and Nb react rapidly with alkenes. From the absence of a measureable pressure dependence of the rate constant over the limited He range of 0.5-0.8 Torr, we infer that bimolecular elimination chemistry occurs. We relate the pattern of reactivity to recent ab initio calculations of the geometry and binding energy of M-C 2 H 4 and H-M-C 2 H 3 for 4d-series transition metals

Kinetics of neutral transition-metal atoms in the gas phase: oxidation reactions of titanium (a3F) from 300 to 600 K

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics of neutral transition-metal atoms in the gas phase: oxidation reactions of titanium (a3F) from 300 to 600 KMark L. Campbell and Roy E. McCleanCite this: J. Phys. Chem. 1993, 97, 30, 7942–7946Publication Date (Print):July 1, 1993Publication History Published online1 May 2002Published inissue 1 July 1993https://doi.org/10.1021/j100132a024RIGHTS & PERMISSIONSArticle Views108Altmetric-Citations58LEARN 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 (511 KB) Get e-Alerts

Reactions of neutral palladium atoms in the gas phase: formation of stable palladium(alkane) complexes at 300 K

The authors and others are surveying the gas-phase reactivity of bare neutral transition metal atoms with alkanes and alkenes. In the 3d series, none of the neutral atoms reacts with alkanes at 300 K, and only Sc, Ti, V, and Ni react with alkenes. Here the authors report state-specific kinetics data for the 4d series. The 4d[sup 10] ([sup 1]S[sub 0]) ground state of the Pd atom reacts rapidly with ethylene, propylene, cyclopropane, and 1-butene and moderately rapidly with ethane, propane, and n-butane at 300 [+-] 5 K in 0.5-0.8 Torr of He. The latter are apparently the first clear-cut examples of gas-phase chemistry between a neutral ground-state transition metal atom and an alkane. Earlier gas-phase studies of Pd reactivity with CH[sub 4] found no reaction of the Pd atom and very slow reaction of the clusters Pd[sub x], x [le] 2. CH[sub 4] is inert to Rh atoms and to Fe atoms. The ground-state Pt atom might react with CH[sub 4], n-hexane, and cyclohexane, but interpretation was complicated by the possible presence of excited-state atoms or of multiphoton ionization and fragmentation. 20 refs., 1 fig., 1 tab.

Kinetics of neutral transition metal atoms in the gas phase: reactions of scandium through copper with alkanes and alkenes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics of neutral transition metal atoms in the gas phase: reactions of scandium through copper with alkanes and alkenesDavid Ritter, John J. Carroll, and James C. WeisshaarCite this: J. Phys. Chem. 1992, 96, 26, 10636–10645Publication Date (Print):December 1, 1992Publication History Published online1 May 2002Published inissue 1 December 1992https://doi.org/10.1021/j100205a014RIGHTS & PERMISSIONSArticle Views161Altmetric-Citations61LEARN 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-Alerts

Mechanisms for the reactions between methane and the neutral transition metal atoms from yttrium to palladium

Calculations including electron correlations have been performed for the oxidative addition reactions between methane and the whole sequence of second row transition metal atoms from yttrium to palladium. The lowest barrier for the C-H insertion reaction is found for the rhodium atom. Palladium has the lowest methane elimination barrier. The barrier height is governed by two factors. In the reactant channel low repulsion favors a low barrier, and in the product channel strong bond formation is important. The atomic state with lowest repulsion toward methane is the d{sup n+2} state and the strongest bonds are formed to the d{sup n+1} s state. For rhodium both these states are energetically low lying. Only palladium has a bound {eta}{sup 2} precursor state on the ground state potential surface. Another interesting result is that the potential surface for the reaction between methane and the rhodium atom is remarkably similar to the potential surface for the reaction between methane and ClRhL{sub 2}, which has been studied experimentally. 44 refs., 5 figs., 5 tabs.

Kinetics of neutral transition-metal atoms in the gas phase: oxidation of scandium(a2D), titanium(a3F), and vanadium(a4F) by nitric oxide, oxygen, and nitrous oxide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics of neutral transition-metal atoms in the gas phase: oxidation of scandium(a2D), titanium(a3F), and vanadium(a4F) by nitric oxide, oxygen, and nitrous oxideDavid. Ritter and James C. WeisshaarCite this: J. Phys. Chem. 1990, 94, 12, 4907–4913Publication Date (Print):June 1, 1990Publication History Published online1 May 2002Published inissue 1 June 1990https://doi.org/10.1021/j100375a028RIGHTS & PERMISSIONSArticle Views186Altmetric-Citations81LEARN 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 (950 KB) Get e-Alerts

Kinetics of neutral transition-metal atoms in the gas phase: oxidation of titanium(a3F) by nitric oxide, oxygen, and nitrous oxide

Etude cinetique en phase gazeuse dans un reacteur a ecoulement avec detection fluorescente induite par laser. La reaction consiste en un transfert d'oxygene

ChemInform Abstract: CHARGE‐OVERLAP STUDY OF MULTIPLE METAL‐METAL BONDING AND CONJUGATION IN LINEAR CHAINS OF TRANSITION‐METAL ATOMS

For a comparative study of bonding, the dsp excited configuration, pertinent to linear digonal hybrids, was imposed on metals of three transition series. Computations of u, r, and 6 overlap of the s, p, and d orbitals in this configuration were made for selected metals, at the usual metallic distance, the distance in A3B superconducting alloys, and the distance for known multiple metal bonds in complexes. The computation made use of single-{ Slater orbitals derived from the same Burns rule for all. Subsequently, molecular orbital calculation of o, r, and 6 bonding for a repeating unit, -(M2)in an infinite chain was made by using an extended Hiickel method and the Mulliken-Wolfsberg and Helmholz approximation. The (same) parameter, K = 1.75, used for all metals was first tested for N2 and P2. The bond stabilization relative to the ground-state atoms, proportional to overlap, was used to approximate the bond dissociation energy. A new attempt was made to justify and to delineate the approximation involved and to show that the neglected two-electron integrals as well as the nuclear repulsion tend to cancel. Coulomb integrals were approximated by valence-orbital ionization energies (VOWS), which for self-consistency were all obtained from existing z-series expansion of the Hartree-Fock SCF energies of the atoms and their ions of appropriate configuration. The dsp configuration energies were also obtained from the same HF-SCF calculations. In cases where data were not available and for the third series the dnsp energies were obtained from weighted averages of spectroscopic term energies given by Moore. Overlap data here support dp hybridization assisted by sp in bonding that is principally do plus d r and d6. The bond strength as well as bond order for a chain peaks at group 6, drops at the first column of group 7, and rises again at group 8. The relative bond strength for do vs. d r vs. d6 bonds was estimated by the ratio of relative stabilizations. Pictures of conjugate bonds and their resonance in a chain, consistent with the translational symmetry of the repeating unit, -(M2)-, and with the conservation of azimuthal angular momentum were drawn. The study suggests that, for a chain of neutral transition-metal atoms, the most favorable multiple bonding occurs for group 5 and group 6 elements (more so for the second series than for the first), the largest number of resonance-conjugation hybrids exists for group 5, and the highest bond order occurs for group 6 atoms.

Charge-overlap study of multiple metal-metal bonding and conjugation in linear chains of transition-metal atoms

For a comparative study of bonding, the dsp excited configuration, pertinent to linear digonal hybrids, was imposed on metals of three transition series. Computations of u, r, and 6 overlap of the s, p, and d orbitals in this configuration were made for selected metals, at the usual metallic distance, the distance in A3B superconducting alloys, and the distance for known multiple metal bonds in complexes. The computation made use of single-{ Slater orbitals derived from the same Burns rule for all. Subsequently, molecular orbital calculation of o, r, and 6 bonding for a repeating unit, -(M2)in an infinite chain was made by using an extended Hiickel method and the Mulliken-Wolfsberg and Helmholz approximation. The (same) parameter, K = 1.75, used for all metals was first tested for N2 and P2. The bond stabilization relative to the ground-state atoms, proportional to overlap, was used to approximate the bond dissociation energy. A new attempt was made to justify and to delineate the approximation involved and to show that the neglected two-electron integrals as well as the nuclear repulsion tend to cancel. Coulomb integrals were approximated by valence-orbital ionization energies (VOWS), which for self-consistency were all obtained from existing z-series expansion of the Hartree-Fock SCF energies of the atoms and their ions of appropriate configuration. The dsp configuration energies were also obtained from the same HF-SCF calculations. In cases where data were not available and for the third series the dnsp energies were obtained from weighted averages of spectroscopic term energies given by Moore. Overlap data here support dp hybridization assisted by sp in bonding that is principally do plus d r and d6. The bond strength as well as bond order for a chain peaks at group 6, drops at the first column of group 7, and rises again at group 8. The relative bond strength for do vs. d r vs. d6 bonds was estimated by the ratio of relative stabilizations. Pictures of conjugate bonds and their resonance in a chain, consistent with the translational symmetry of the repeating unit, -(M2)-, and with the conservation of azimuthal angular momentum were drawn. The study suggests that, for a chain of neutral transition-metal atoms, the most favorable multiple bonding occurs for group 5 and group 6 elements (more so for the second series than for the first), the largest number of resonance-conjugation hybrids exists for group 5, and the highest bond order occurs for group 6 atoms.

Relativistic contributions to the low-lying excitation energies and ionization potentials of the transition metals

Numerical Hartree–Fock calculations have been performed for the lowest terms of the dns2, dn+1s, and dn+2 configurations of the neutral transition metal atoms and the dns and dn+1 configurations of the ions. The excitation energies and ionization potentials are compared with their relativistic counterparts calculated according to the approximate scheme of Cowan and Griffin. The relativistic corrections are large, surprisingly so even for the first transition series, and act to stabilize ’’s-electron rich’’ configurations. They are thus of opposite sign to the electron correlation contributions, which generally tend to stabilize ’’d-electron rich’’ configurations. These correlation effects are particularly severe towards the end of the first transition series. Estimates for relativistic corrections from perturbation theory agree well with relativistic SCF calculations for the first and second transition series but depart substantially for the third series. The excitation and ionization energies from the relativistic calculations are compared with the experimental values (averaged over J states) to observe the overall trends in the correlation contributions.

Analytic Self-Consistent-Field Wave Functions for Transition-Metal Atoms

Analytic Hartree-Fock-Roothaan calculations have been carried out for the states arising from the $3{d}^{n}4{s}^{2}$ configurations for neutral transition-metal atoms and from the $3{d}^{n}$ configurations for the doubly ionized ions. The atomic orbitals have been expanded in terms of linear combinations of Slater-type functions, 21 of them for the neutral atoms and 18 for the doubly ionized ions.