Zhiling Liu

Structural Evolution of Homoleptic Heterodinuclear Copper-Nickel Carbonyl Anions Revealed Using Photoelectron Velocity-Map Imaging

The homoleptic heterodinuclear copper-nickel carbonyl anions CuNi(CO)n(-) (n = 2-4) were generated in a pulsed-laser vaporization source and investigated using photoelectron velocity-map imaging spectroscopy. The electron affinities of CuNi(CO)2 (2.15 ± 0.03 eV), CuNi(CO)3 (2.30 ± 0.03 eV), and CuNi(CO)4 (1.90 ± 0.04 eV) were deduced from the photoelectron spectra. Theoretical calculations at the B3LYP level were carried out to elucidate the structures and the electronic properties of CuNi(CO)n(0/1-) (n = 1-4) and to support the experimental observations. Comprehensive comparisons between experiments and calculations suggest that there is a turnover point of the absorption site during the progressive carbonylation process. The carbonyl groups are determined to be preferentially bonded to the nickel atom. When the nickel center satisfies the 18-electron configuration, the copper atom starts to adsorb additional CO molecules. These results will shed light on the bonding mechanisms of the heterometallic carbonyl clusters.

Photoelectron Velocity Map Imaging Spectroscopy of Lead Tetracarbonyl-Iron Anion PbFe(CO)4(.).

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.

Octacoordinate metal carbonyls of scandium and yttrium: theoretical calculations and experimental observation

RATIONALE The transition metal carbonyls are among the most important complexes in coordination chemistry. The maximum coordination number in these complexes is seven. Because the cations Sc(+) and Y(+) have empty second outermost d orbital subshells, they can possibly bond eight CO ligands, forming the 18-electron d(10)s(2)p(6) noble gas configuration. The aim of this study is to determine whether the octacoordinate metal carbonyls of Sc(+) and Y(+) exist. METHODS The structures and bonding of M(CO)n(+) (M = Sc and Y, n = 7-9) were studied using Density Functional Theory (DFT) calculations with the functionals of B3LYP and BP86. The cationic complexes from laser ablation of Sc and Y in CO gas were analyzed by time-of-flight mass spectrometry. RESULTS The structures of M(CO)n(+) (M = Sc and Y, n = 7-9) and the bond dissociation energies for the last CO ligand in M(CO)n(+) (M = Sc and Y, n = 8 and 9) were obtained using DFT calculations. The products in the experiment for both metals include the series MO(CO)n(+), MO(H2O)(CO)n(+) and M(CO)n(+) (M = Sc or Y). The intensities of the MO(CO)n(+) and MO(H2O)(CO)n(+) ions change gradually with the number of CO ligands, while most M(CO)n(+) ions are very weak except for three intense ones, Sc(CO)7(+), Sc(CO)8(+) and Y(CO)8(+). CONCLUSIONS Comparisons between the theoretical calculations and the experimental observations indicate that eight CO ligands are chemically bonded on the central atom in the singlet state of Sc(CO)8(+) ((1)A1 state of D(4d) symmetry) and the singlet and triplet states of Y(CO)8(+) ((1)A1 state of D(4d) symmetry and (3)A(1g) state of O(h) symmetry). The (1)A1 states of both Sc(CO)8(+) and Y(CO)8(+) have the 18-electron d(10)s(2)p(6) noble gas configuration. In M(CO)9(+) (M = Sc or Y), the ninth CO is weakly adsorbed on the external shell.

Structure of Au40/−1 in the gas phase: A joint geometry relaxed ab initio calculations and vibrationally resolved photoelectron imaging investigation

We have combined photoelectron velocity-map imaging spectroscopy and high-level ab initio calculations to elucidate the geometries of Au4 (0/-1). Well-resolved ground-state electronic transition was observed in the photoelectron spectrum of Au4 (-) at 446 nm, leading to more accurate electron affinity and vibrational frequencies for the ground state of the neutral Au4 (-). The pure and vibrationally resolved spectra provide definitive experimental evidence for the resolution of the ground-state gold tetramer in the gaseous phase, with the aid of the ab initio calculations and Franck-Condon simulations. The comprehensive comparisons between the experiment and theoretical calculations suggest that the Y-shaped structure is the global minimum for both the neutral and anionic Au4.

Photoelectron imaging and theoretical study on the structure and chemical binding of the mixed- ligand M(I) complexes, [HMSH](-) (M = Cu, Ag, and Au)

We have reported a combined photoelectron imaging and theoretical study on gaseous mixed-ligand M(I) complexes of [HMSH](-) (M = Cu, Ag, and Au). With the aid of Franck-Condon simulations, vibrationally resolved photoelectron spectra yield accurate electron affinities of 3.269(6), 3.669(10), and 3.591(6) eV for [HCuSH], [HAgSH], and [HAuSH], respectively. And low-frequency modes are observed: 368(12) cm(-1) for [HCuSH], 286(12) cm(-1) for [HAgSH], and 327(12) cm(-1) for [HAuSH], respectively. Extensive theoretical calculations are performed to aid in the spectral assignments and the calculated values agree well with the experimental observations. Although the S and H atoms have little discrepancy in electronegativity (2.20 for H and 2.54 for S), distinct bonding properties are demonstrated between H-M and M-S bond. It is revealed that there exists significant ionic bonding between M-S in [HMSH](-) (M = Cu, Ag, and Au), while a gradual transition from ionic behavior between H-Cu in [HCuSH](-) to quite strong covalent bonding between H-Au in [HAuSH](-), supported by a variety of chemical bonding analyses.

Low-energy photoelectron imaging of HS2 anion

Low-energy photoelectron imaging of HS2 (-) has been investigated, which provides the vibrational frequencies of the ground state as well as the first excited state of HS2. It allows us to determine more accurate electron affinity of HS2, 1.9080 ± 0.0018 eV. Combined with Frank-Condon simulation, the vibrational features have been unveiled related to S-S stretching and S-S-H bending modes for the ground state and S-S stretching, S-S-H bending, and S-H stretching modes for the first excited state. Photoelectron angular distributions are mainly characteristic of electron detachment from two different molecular orbitals (MOs) in HS2 (-). With the aid of accurate electron affinity value of HS2, corresponding thermochemical quantities can be accessed.

Vibrationally Resolved Photoelectron Imaging of Cu2H- and AgCuH- and Theoretical Calculations

Vibrationally resolved photoelectron spectra have been obtained for Cu(2)H(-) and AgCuH(-) using photoelectron imaging at 355 nm. Two transition bands X and A are observed for each spectrum. The X bands in both spectra show the vibration progressions of the Cu-H stretching mode and the broad peaks of these progressions indicate significant structural changes from Cu(2)H(-) and AgCuH(-) to their neutral ground states. The A bands in the spectra of Cu(2)H(-) and CuAgH(-) show stretching progressions of Cu-Cu and Ag-Cu, respectively. The contours of these two progressions are pretty narrow, indicating relatively small structural changes from Cu(2)H(-) and AgCuH(-) to their neutral excited states. Calculations based on density functional theory indicate that the ground states of Cu(2)H(-) and AgCuH(-) and the first excited states of their neutrals are linear, whereas their neutral ground states are bent. The photoelectron detachment energies and vibrational frequencies from these calculations are in good agreement with the experimental observations. Especially, the theoretical predication of linear structures for the anions and the neutral excited states are supported by the spectral features of A bands, in which the bending modes are inactive. Comparisons among the vertical detachment energies of Cu(2)H(-), AgCuH(-), and their analogs help to elucidate electronic characteristics of coinage metal elements and hydrogen in small clusters.

Observing the Transition from Equatorial to Axial CO Chemisorption: Infrared Photodissociation Spectroscopy of Yttrium Oxide-Carbonyls.

A series of yttrium oxide-carbonyls are prepared via a laser vaporization supersonic cluster source in the gas phase and identified by mass-selected infrared photodissociation (IRPD) spectroscopy in the C-O stretching region and by comparing the observed IR spectra with those from quantum chemical calculations. For YO(CO)4(+), all four CO ligands prefer to occupy the equatorial site of the YO(+) unit, leading to a quadrangular pyramid with C4v symmetry. Two energetically nearly degenerate isomers are responsible for YO(CO)5(+), in which the fifth CO ligand is either inserted into the equatorial plane of YO(CO)4(+) or coordinated opposite the oxygen on the C4 axis. YO(CO)6(+) has a pentagonal bipyramidal structure with C5v symmetry, which includes five equatorial CO ligands and one axial CO ligand. The present IRPD spectroscopic and theoretical study of YO(CO)n(+) extends the first shell coordination number of CO ligands in metal monoxide carbonyls to six. The transition from equatorial to axial CO chemisorption in these yttrium oxide-carbonyls is fortunately observed at n = 5, providing new insight into ligand interactions and coordination for the transition metal oxides.

Vibrationally Resolved Photoelectron Imaging of Au3H

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).

An investigation into low-lying electronic states of HCS2 via threshold photoelectron imaging

Low-energy photoelectron imaging spectra of HCS2(-) are reported for the first time. Vibrationally resolved photodetachment transitions from the ground state of HCS2(-) to the ground state and low-lying excited states of HCS2 are observed. Combined with the ab intio calculations and Franck-Condon simulations, well-resolved vibrational spectra demonstrate definitive evidence for the resolution of the ground-state and excited states of HCS2 radical in the gaseous phase. The ground state and two low-lying excited states of HCS2 radical are assigned as (2)B2, (2)A2, and (2)A1 states, respectively. The adiabatic electron affinity is determined to be 2.910 ± 0.007 eV. And the term energies of the excited states, T0 = 0.451 ± 0.009 eV and 0.553 ± 0.009 eV, are directly measured from the experimental data, respectively. Angular filtering photoelectron spectra are carried out to assist in the spectral band assignment.