Search

Theoctacoordinate metal carbonyls La(CO)8+andCe(CO)8+were observed in laser vaporizationof La and Ce in pure CO gas. The peak intensities in the mass spectra,the infrared photodissociation spectra, and the theoretical calculationsindicate that all CO ligands in these two complexes are bonded withthe central metal atoms. The CO stretching frequencies in La(CO)8+and Ce(CO)8+are determinedto be 2110 and 2108 cm–1, respectively. Theoreticalstudies indicate that the most stable structures for La(CO)8+and Ce(CO)8+are an Ohgeometry at its triplet state and aslightly distorted Ohgeometry at its quartet state, respectively. These two complexesrepresent new octacoordinate metal carbonyls after previously determinedU(CO)8+and Y(CO)8+. [ABSTRACT FROM AUTHOR]

Vibrationally resolved photoelectronspectra have been obtainedfor Cu2H–and AgCuH–using photoelectron imaging at 355 nm. Two transition bands X andA are observed for each spectrum. The X bands in both spectra showthe vibration progressions of the Cu–H stretching mode andthe broad peaks of these progressions indicate significant structuralchanges from Cu2H–and AgCuH–to their neutral ground states. The A bands in the spectra of Cu2H–and CuAgH–show stretchingprogressions of Cu–Cu and Ag–Cu, respectively. The contoursof these two progressions are pretty narrow, indicating relativelysmall structural changes from Cu2H–andAgCuH–to their neutral excited states. Calculationsbased on density functional theory indicate that the ground statesof Cu2H–and AgCuH–and the first excited states of their neutrals are linear, whereastheir neutral ground states are bent. The photoelectron detachmentenergies and vibrational frequencies from these calculations are ingood agreement with the experimental observations. Especially, thetheoretical predication of linear structures for the anions and theneutral excited states are supported by the spectral features of Abands, in which the bending modes are inactive. Comparisons amongthe vertical detachment energies of Cu2H–, AgCuH–, and their analogs help to elucidate electroniccharacteristics of coinage metal elements and hydrogen in small clusters. [ABSTRACT FROM AUTHOR]

Bimetallic clusters of AgCu–, AgCu2–, and Ag2Cu–areinvestigated by using photoelectron imaging and theoretical calculations.Their photoelectron spectra have been obtained at the wavelength of355 nm and that of AgCu–is also acquired at 1064nm. The ground state vertical detachment energies of these three clustersare measured to be 0.96 (1), 2.39 (5), and 2.41 (5) eV. The groundstate adiabatic detachment energy of AgCu–is measuredto be 0.93 (1) eV. Other spectroscopic constants of AgCu–including its frequency, bond length, and dissociation energy (relativeto the products Ag–and Cu) are determined to be191(15) cm–1, 2.487(10) Å, and 1.39 eV accordingto its spectrum at 1064 nm. Only upper limits of the ground stateadiabatic detachment energies of AgCu2–and Ag2Cu–are estimated by using theirspectra at 355 nm. The structures and properties of AgCu–, AgCu2–, Ag2Cu–, and their neutral counterparts are also computed by using a strategywhere the structural optimizations are performed with the PW91PW91method and the energy calculations are performed with the CCSD (T)method. The calculations are in better agreement with the experimentsthan most of the previous theoretical work. [ABSTRACT FROM AUTHOR]

Joint research of photoelectron velocity map imaging spectroscopy and density functional theory has been performed to probe the geometrical structures and electronic properties for heterodinuclear iron-lead carbonyl cluster PbFe(CO)4-, which serves as a monomer of the metal-metal bonded oligomer. The photoelectron detachment of PbFe(CO)4- is recorded at two different photon energies with rich spectral features. The ground-state transition obtained at 532 nm reveals a broad vibrationally resolved spectral band, which corresponds to the lead-iron stretching, while the 355 nm spectrum displays many more transitions on the higher-energy side, which correspond to the electronic excited states of PbFe(CO)4. Theoretical calculations at the B3LYP level are performed to explore the ground states of both the anionic and neutral PbFe(CO)4 and to support spectral identification of the fine resolved photoelectron spectra. Moreover, the unique chemical bonding between lead and iron in PbFe(CO)4 is discussed with the aid of natural bond orbital analyses. [ABSTRACT FROM AUTHOR]

The reactions of the iridium dimer anion [Ir 2 ] - with acetylene have been studied by mass spectrometry in the gas phase, which indicate that the [Ir 2 ] - anion can consecutively react with C 2 H 2 molecules to form the [Ir 2 C 2 x ] - ( x = 1, 2) and [Ir 2 C 2 y H 2 ] - ( y = 3-5) anions as major products with the successive release of H 2 molecules at room temperature. The reactions are confirmed by the reactions of the mass-selected product [Ir 2 C 2 ] - anion with C 2 H 2 to produce [Ir 2 C 4 ] - and [Ir 2 C 2 y H 2 ] - ( y = 3-5). Photoelectron spectra and quantum chemistry calculations confirm that the [Ir 2 C 2 x ] - ( x = 1, 2) product anions possess cyclic [Ir(μ-C) 2 Ir] - and [Ir(μ-C)(μ-C 3 )Ir] - structures, implying that the robust C≡C triple bond of acetylene can be completely cleaved by the [Ir 2 ] - anion.

A series of heteronuclear group 5 metal-nickel carbonyls MNi(CO) 7 - (M = V, Nb, Ta) have been generated via a laser ablation ion source and studied by photoelectron velocity-map imaging spectroscopy. Quantum chemical calculations have been performed to probe the electronic and geometric structures and help to assign the spectra. The adiabatic detachment energies (ADEs) and vertical detachment energies (VDEs) are deduced from spectra to be 3.40/3.58, 3.34/3.55, 3.30/3.50 eV, which are consistent with quantum chemical computational results. The MNi(CO) 7 - (M = V, Nb, Ta) consists of three bridging carbonyls, one carbonyl terminally bonded to the Ni atom and three carbonyls terminally bonded to the M (M = V, Nb, Ta) atom. These geometries are different from homobinuclear Cr 2 (CO) 7 + , Ni 2 (CO) 7 + , Pd 2 (CO) 7 + , and Fe 2 (CO) 7 - and heterobinuclear CuFe(CO) 7 - , CoZn(CO) 7 + , and CO is largely activated by a bridging coordination mode. The experimental and theoretical results would provide important information to understand the chemisorbed CO molecules on alloy surfaces or interfaces, which is of great significance to elucidate CO molecule activation processes.

The CO chemisorption onto the ScO + cation was investigated using infrared photodissociation spectroscopy combined with density functional theory calculations. The spectra were recorded in the CO stretching vibrational region for the OSc(CO) n + ( n = 4-6) complex series. Comparisons of the experimental spectra with the simulated ones have established the geometries and present strong evidence that all of the CO ligands are chemisorbed, which could not be readily oxidized by scandium monoxide core into CO 2 . Complementary calculations demonstrate that, regardless of the thermodynamic feasibility, the CO oxidation on the scandium monoxide carbonyl complexes is kinetically unfavorable due to the significant barriers involved in the CO oxidation process. Nevertheless, the consecutive CO adsorption has a positive influence on the Sc-O bond activation.

Infrared spectra of the neutral dimethylamine-methanol cluster, DMA-CH 3 OH, were measured in the spectral range of 2800-3900 cm -1 using an infrared-vacuum ultraviolet (IR-VUV) scheme. Quantum chemical calculations and ab initio molecular dynamic (AIMD) simulations were carried out to understand the experimental spectral features. Experimental and theoretical results reveal the coexistence of N···HO and O···HN hydrogen-bonded structures. AIMD simulations show that the methyl group in methanol internally rotates around the N···O axis, addressing the dynamic effect of the fluctuation of hydrogen bonds on the vibrational features. The bonding analysis was performed to elucidate the nature of the intermolecular interaction between DMA and CH 3 OH. The present work provides the fundamental understanding of hydrogen-bonding networks in the amine-alcohol complexes.

Gas-phase infrared photodissociation spectra of [V(CO 2 ) n ] + complexes revealed three new vibrational bands at 1140, 1800, and 3008 cm -1 at n = 7, the features of which are retained in the larger clusters (Ricks, A. M.; Brathwaite, A. D.; Duncan, M. A. J. Phys. Chem. A 2013, 117, 11490-11498). However, structural assignment of this intriguing feature remains open. Herein, quantum chemical calculations on [V(CO 2 ) 7 ] + were carried out to identify the structure of the low-lying isomers and to assign the observed spectral features. The comparison of calculated infrared spectra of [V(CO 2 ) 7 ] + with experimental infrared spectra identified the formation of a bent CO 2 - species, suggesting the ligand-induced activation of CO 2 by the vanadium cation. The structures and infrared spectra of [Cr(CO 2 ) 7 ] + and [Mn(CO 2 ) 7 ] + were also predicted and discussed.

Heterobimetallic lanthanum-nickel and cerium-nickel carbonyls, LnNi(CO) n - (Ln = La, Ce; n = 2-5), were generated using a pulsed laser vaporization/supersonic expansion ion source. These compounds were characterized by photoelectron velocity-map imaging spectroscopy and quantum chemical calculations. The binding motif in the most stable isomers of the n = 2 and 3 clusters consists of one side-on-bonded carbonyl. A new building block of two side-on-bonded carbonyls is favored at n = 4, which is retained at n = 5, evidencing the increase of the number of extremely activated CO molecule in the larger clusters. The experimental and theoretical results demonstrate the ligand-enhanced CO activation by the early lanthanide-nickel heterodimers, which would have important implications for the design of alloy catalysts for activation of a molecular ligand.

Photoelectron velocity-map imaging spectroscopy was conducted for the heterotrinuclear metal carbonyls V 2 Ni(CO) n - (n = 6-10). Electronic structure calculations were performed to understand the experimental spectral features. The binding motif of a V-V-Ni chain with two side-on-bonded carbonyls and two bridging carbonyls is favored in the n = 6-9 clusters. A V 2 Ni triangle core structure is formed at n = 10 with the involvement of two carbonyls with the carbon atom triply coordinated to metal atoms, three bridging carbonyls, and five terminal carbonyls, in which CO bonding configurations mirror the adsorption features in the three-fold hollow, bridging, and atop sites on the closely packed surface, respectively. The present study provides a stepwise picture for molecular level understanding of CO bonding on heteronuclear metal clusters, which is directly relevant to the elementary processes of CO on the alloy surfaces/interfaces.

The methylamine dimer, (CH 3 NH 2 ) 2 , is a model system to study the CH 3 and NH 2 spectral patterns in the neutral microsolvated systems relevant to chemical biology, atmospheric chemistry, and catalysis. We report infrared-vacuum ultraviolet spectroscopic measurements to probe the neutral (CH 3 NH 2 ) 2 . Quantum chemical calculations and ab initio molecular dynamics simulations were performed to understand the observed spectral features. Experimental and theoretical results indicate the likely coexistence of both cis and trans structures. A salient feature of this work is that the peak widths are not significantly affected by the structural transformation and the fluctuation of hydrogen bond distance, allowing the stretching modes to be clearly resolved.

The reaction of copper and silver cations with carbon dioxide was studied by mass-selected infrared photodissociation spectroscopy. Quantum chemical calculations were performed on these products, which aided the experimental assignments of the infrared spectra and helped to elucidate the geometrical and electronic structures. The Cu + and Ag + cations bind to an oxygen atom of CO 2 in an end-on configuration via a charge-quadrupole electrostatic interaction in the [M(CO 2 ) n ] + complexes. The formation of oxide-carbonyl and carbonyl-carbonate structures is not favored for the interaction of CO 2 with Cu + and Ag + . For n = 3 and 4, the n + 0 structure is preferred. [Note on the nomenclature: Using i + j, i denotes the number of CO 2 molecules in the first coordination shell, and j denotes the number of CO 2 molecules in the second coordination shell.] The two nearly energy-identical n + 0 and (n - 1) + 1 structures coexist in n = 5 and 6. While the six-coordinated structure is favored for [Cu(CO 2 ) n=7,8 ] + , the n + 0 configuration is dominated in [Ag(CO 2 ) n=7,8 ] + . The reaction of CO 2 with the cationic metal atoms has been compared to that with the neutral and anionic metal atoms, which would have important implications for understanding the interaction of CO 2 with reduction catalysts and rationally designing catalysts for CO 2 reduction based on cost-effective transition metals.

Because of renewed research on thorium-based molten salt reactors, there is growing demand and interest in enhancing the knowledge of thorium chemistry both experimentally and theoretically. Compared with uranium, thorium has few chemical studies reported up to the present. Here we report the vibrationally resolved photoelectron imaging of the thorium monoxide anion. The electron affinity of ThO is first reported to be 0.707 ± 0.020 eV. Vibrational frequencies of the ThO molecule and its anion are determined from Franck-Condon simulation. Spectroscopic evidence is obtained for the two-electron transition in ThO - , indicating the strong electron correlation among the (7s σ ) 2 (6d δ ) 1 electrons in ThO - and the (7s σ ) 2 electrons in ThO. These findings are explained by using quantum-chemical calculations including spin-orbit coupling, and the chemical bonding of gaseous ThO molecules is analyzed. The present work will enrich our understanding of bonding capacities with the 6d valence shell.

Joint research of photoelectron velocity map imaging spectroscopy and density functional theory has been performed to probe the geometrical structures and electronic properties for heterodinuclear iron-lead carbonyl cluster PbFe(CO)4(-), which serves as a monomer of the metal-metal bonded oligomer. The photoelectron detachment of PbFe(CO)4(-) is recorded at two different photon energies with rich spectral features. The ground-state transition obtained at 532 nm reveals a broad vibrationally resolved spectral band, which corresponds to the lead-iron stretching, while the 355 nm spectrum displays many more transitions on the higher-energy side, which correspond to the electronic excited states of PbFe(CO)4. Theoretical calculations at the B3LYP level are performed to explore the ground states of both the anionic and neutral PbFe(CO)4 and to support spectral identification of the fine resolved photoelectron spectra. Moreover, the unique chemical bonding between lead and iron in PbFe(CO)4 is discussed with the aid of natural bond orbital analyses.

We first demonstrate the photoelectron spectroscopic evidence of the transition of two competitive solvation patterns in the Au(-)(CH3OH)n (n = 1-5) clusters. Quantum chemical calculations have been carried out to characterize the geometric structures, energy properties and hydrogen-bonded patterns, and to aid the spectral assignment. It has been found that the nonconventional hydrogen bonds dominate the small clusters (n = 1 and 2), whereas the conventional hydrogen bonds play more and more important role from n = 2 to n = 5. This finding provides concrete hydrogen bond network evolution of Au(-) surrounded by methanol molecules.

We report a combined photoelectron velocity map imaging spectroscopy and density functional theory investigation on the Au3H(-) anion. Transition between the anionic electronic ground state and the neutral electronic ground state is revealed. Vibrationally resolved spectra were recorded at two different photon energies, providing a wealth of spectroscopic information for the electronic ground state of the Au3H. Franck-Condon simulations of the ground-state transition are carried out to assist in the assignment of the vibrationally resolved spectra. The electron affinity and vertical detachment energy of Au3H are measured to be 2.548 ± 0.001 and 2.570 ± 0.001 eV, respectively. Three stretching vibrational modes are determined to be activated upon photodetachment, with the frequencies of 2100 ± 100, 177 ± 10, and 96 ± 10 cm(-1).

Bimetallic clusters of MPb5(-) (M = Cu, Ag, and Au) have been studied using density functional theory and photoelectron imaging spectroscopy. These anionic clusters and their neutrals were determined to be a Pb5 trigonal bipyramid with the coinage metal atom on its triangular facet. This structure of each MPb5(-) or MPb5 was found to be more than 0.5 eV lower than other structural candidates and that of each MPb5(-) has a HOMO-LUMO gap of larger than 1.2 eV. The chemical bonding between M and Pb5 in MPb5(-) was dominantly attributed to the interaction between the outer s orbital of M and the lowest unoccupied molecular orbital (LUMO) of Pb5. The inner d orbitals of M and the occupied orbitals of Pb5 unit only make a little contribution. The different bonding behaviors of Cu, Ag, and Au, which are noticeable in many other species, have little effect on the Pb5 counterpart in MPb5(-), indicating Pb5 unit acts partially like a large artificial atom. Additionally, photoelectron spectra of MPb5(-) (M = Cu, Ag, and Au) provide good experimental data to evaluate different theoretical approaches dealing with relativistic effects in clusters containing heavy atoms.

Photodetachment of AgX(-) (X = Cl, Br, I) and AuCl(-) is studied by a photoelectron velocity map imaging technique and theoretical calculations. Photoelectron spectra (PES) and photoelectron angular distributions (PADs) were obtained. The vibrationally resolved spectra provided approximately equal electron affinities (EAs) for AgX: 1.593(22) eV for AgCl, 1.623(21) eV for AgBr, and 1.603(22) eV for AgI, respectively. Franck-Condon simulations of these spectra gave the equilibrium bond lengths and vibrational frequencies of the title anions. Relativistic density functional theory (DFT) calculations using BLYP, PW91, PBE, and BP86 functionals have been performed to predict the EAs of the AgX (X = Cl, Br, I) molecules. The computed EAs at the BP86 level of theory are in good agreement with the experimental values. Energy partitioning analyses (EPA) at the BP86(ZORA)/QZ4P level of theory of both anions and their neutrals were reported.

The photoelectron images of Ag(-)(H(2)O)(x) (x=1,2) and AgOH(-)(H(2)O)(y) (y=0-4) are reported. The Ag(-)(H(2)O)(1,2) anionic complexes have similar characteristics to the other two coinage metal-water complexes that can be characterized as metal atomic anion solvated by water molecules with the electron mainly localized on the metal. The vibrationally well-resolved photoelectron spectrum allows the adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of AgOH(-) to be determined as 1.18(2) and 1.24(2) eV, respectively. The AgOH(-) anion interacts more strongly with water molecules than the Ag(-) anion. The photoelectron spectra of Ag(-)(H(2)O)(x) and AgOH(-)(H(2)O)(y) show a gradual increase in ADE and VDE with increasing x and y due to the solvent stabilization., (© 2011 American Chemical Society)

Photodetachment of group 11 cyanide anions MCN(-) (M = Cu, Ag, Au) has been investigated using photoelectron velocity-map imaging. The electron affinities (EAs) of CuCN (1.468(26)) and AgCN (1.602(22)) are larger, while that of AuCN (2.066(8)) is smaller than those of the free atoms. This intriguing observation was confirmed by theoretical studies and was assigned to the transition between ionic and covalent bond properties. The harmonic frequencies of the extended vibrational progressions in the M-C stretching mode are 460(50), 385(27), and 502(10) cm(-1), respectively, which suggests a stronger bond for Au-CN than for Ag-CN. Electronic structure analysis and model calculations suggest that all M-C bonds in group 11 cyanides are best described as single bonds. A model has been proposed to explain how the relativistic effects influence the Au-C bond strength in AuCN.