Activation of Water by Pentavalent Actinide Dioxide Cations: Characteristic Curium Revealed by a Reactivity Turn after Americium.

Swapping of an oxygen atom of water with that of a pentavalent actinide dioxide cation, AnO2+ also called an "actinyl", requires activation of an An-O bond. It was previously found that such oxo exchange in the gas phase occurs for the first two actinyls, PaO2+ and UO2+, but not the next two, NpO2+ and PuO2+. The An-O bond dissociation energies (BDEs) decrease from PaO2+ to PuO2+, such that the observation of a parallel decrease in the An-O bond reactivity is intriguing. To elucidate oxo exchange, we here extend experimental studies to AmO2+, americyl(V), and CmO2+, curyl(V), which were produced in remarkable abundance by electrospray ionization of Am3+ and Cm3+ solutions. Like other AnO2+, americyl(V) and curyl(V) adsorb up to four H2O molecules to form tetrahydrates AnO2(H2O)4+ with the actinide hexacoordinated by oxygen atoms. It was found that AmO2+ does not oxo-exchange, whereas CmO2+ does, establishing a "turn" to increasing the reactivity from americyl to curyl, which validates computational predictions. Because oxo exchange occurs via conversion of an actinyl(V) hydrate, AnO2(H2O)+, to an actinide(V) hydroxide, AnO(OH)2+, it reflects the propensity for actinyl(V) hydrolysis: PaO2+ hydrolyzes and oxo-exchanges most easily, despite the fact that it has the highest BDE of all AnO2+. A reexamination of the computational results for actinyl(V) oxo exchange reveals distinctive properties and chemistry of curyl(V) species, particularly CmO(OH)2+

Activation of Water by Pentavalent Actinide Dioxide Cations: Characteristic Curium Revealed by a Reactivity Turn after Americium.

Swapping of an oxygen atom of water with that of a pentavalent actinide dioxide cation, AnO2+ also called an "actinyl", requires activation of an An-O bond. It was previously found that such oxo exchange in the gas phase occurs for the first two actinyls, PaO2+ and UO2+, but not the next two, NpO2+ and PuO2+. The An-O bond dissociation energies (BDEs) decrease from PaO2+ to PuO2+, such that the observation of a parallel decrease in the An-O bond reactivity is intriguing. To elucidate oxo exchange, we here extend experimental studies to AmO2+, americyl(V), and CmO2+, curyl(V), which were produced in remarkable abundance by electrospray ionization of Am3+ and Cm3+ solutions. Like other AnO2+, americyl(V) and curyl(V) adsorb up to four H2O molecules to form tetrahydrates AnO2(H2O)4+ with the actinide hexacoordinated by oxygen atoms. It was found that AmO2+ does not oxo-exchange, whereas CmO2+ does, establishing a "turn" to increasing the reactivity from americyl to curyl, which validates computational predictions. Because oxo exchange occurs via conversion of an actinyl(V) hydrate, AnO2(H2O)+, to an actinide(V) hydroxide, AnO(OH)2+, it reflects the propensity for actinyl(V) hydrolysis: PaO2+ hydrolyzes and oxo-exchanges most easily, despite the fact that it has the highest BDE of all AnO2+. A reexamination of the computational results for actinyl(V) oxo exchange reveals distinctive properties and chemistry of curyl(V) species, particularly CmO(OH)2+

ARTICLE Probing the nature of gold-carbon bonding in gold-alkynyl complexes

Homogeneous catalysis by gold involves organogold complexes as precatalysts and reaction intermediates. Fundamental knowledge of the gold-carbon bonding is critical to understanding the catalytic mechanisms. However, limited spectroscopic information is available about organogolds that are relevant to gold catalysts. Here we report an investigation of the gold-carbon bonding in gold(I)-alkynyl complexes using photoelectron spectroscopy and theoretical calculations. We find that the gold-carbon bond in the ClAu-CCH À complex represents one of the strongest gold-ligand bonds-even stronger than the known gold-carbon multiple bonds, revealing an inverse correlation between bond strength and bond order. The gold-carbon bond in LAuCCH À is found to depend on the ancillary ligands and becomes stronger for more electronegative ligands. The strong gold-carbon bond underlies the catalytic aptness of gold complexes for the facile formation of terminal alkynyl-gold intermediates and activation of the carbon-carbon triple bond

Resonant tunneling through the repulsive Coulomb barrier of a quadruply charged molecular anion

Multiply charged anions possess a repulsive Coulomb barrier (RCB) against electron emission, thus allowing for long-lived metastable species with negative electron binding energies. For the prototypical multianion, bisdisulizole tetra-anion, we demonstrate that electronically excited states supported by the RCB can undergo resonant tunneling. The dynamics of this process was investigated by one-photon photoelectron imaging and femtosecond pump-probe photoelectron spectroscopy and confirmed by theoretical calculations. Efficient resonant tunneling emission of electrons from the excited states of multianions may be common for systems with sufficiently large RCB. This may provide new opportunities to study electron emission dynamics in complex systems. Multiply charged anions (MCAs) are common in the condensed phase Photoelectron spectroscopy (PES) has been an important technique to probe the RCB and electronic stability of MCAs Here we report a direct observation of a resonant tunneling state in the bisdisulizole tetra-anion [BDSZ 4− , see The PES experiment was performed with an electrospray PES apparatus equipped with a magnetic-bottle electron analyze

Photoelectron Spectroscopy of Palladium(I) Dimers with Bridging Allyl Ligands

The dianionic Pd^I dimers [TBA]₂[(TPPMS)₂Pd₂(μ-C₃H₅)₂] (<b>1</b>) [TBA = tetrabutylammonium, TPPMS = PPh₂(3-C₆H₄SO₃)⁻] and [TBA]₂[(TPPMS)₂Pd₂(μ-C₃H₅)­(μ-Cl)] (<b>2</b>), containing two bridging allyl ligands and one bridging allyl ligand and one bridging chloride ligand, respectively, were synthesized. The electronic structures of these complexes were investigated by combining electrospray mass spectrometry with gas phase photodetachment photoelectron spectroscopy. The major difference between the photoelectron spectra of the anions of <b>1</b> and <b>2</b> is the presence of a low-energy detachment band with an adiabatic electron detachment energy of 2.44(6) eV in <b>1</b>, which is not present in <b>2</b>. The latter has a much higher adiabatic electron detachment energy of 3.24(6) eV. Density functional theory calculations suggest that this band is present in <b>1</b> due to electron detachment from the out-of-phase combination of the π₂ orbitals, which are localized on the terminal carbon atoms of the bridging allyl ligands. In <b>2</b>, the Pd centers stabilize the single π₂ orbital of the bridging allyl ligand, and it is lowered in energy. The presence of the high-energy out-of-phase combination of the π₂ allyl orbitals makes <b>1</b> a better nucleophile, which explains why species with two bridging allyl ligands react with CO₂ in an analogous fashion to momoneric Pd η¹-allyls, whereas species with one bridging allyl and one bridging chloride ligand are unreactive

Probing the Electronic Structure and Chemical Bonding in Tricoordinate Uranyl Complexes UO₂X₃^– (X = F, Cl, Br, I): Competition between Coulomb Repulsion and U–X Bonding

While uranyl halide complexes [UO₂(halogen)_<i>n</i>]^2–<i>n</i> (<i>n</i> = 1, 2, 4) are ubiquitous, the tricoordinate species have been relatively unknown until very recently. Here photoelectron spectroscopy and relativistic quantum chemistry are used to investigate the bonding and stability of a series of gaseous tricoordinate uranyl complexes, UO₂X₃^– (X = F, Cl, Br, I). Isolated UO₂X₃^– ions are produced by electrospray ionization and observed to be highly stable with very large adiabatic electron detachment energies: 6.25, 6.64, 6.27, and 5.60 eV for X = F, Cl, Br, and I, respectively. Theoretical calculations reveal that the frontier molecular orbitals are mainly of uranyl U–O bonding character in UO₂F₃^–, but they are from the ligand valence <i>n</i>p lone pairs in the heavier halogen complexes. Extensive bonding analyses are carried out for UO₂X₃^– as well as for the doubly charged tetracoordinate complexes (UO₂X₄^2–), showing that the U–X bonds are dominated by ionic interactions with weak covalency. The U–X bond strength decreases down the periodic table from F to I. Coulomb barriers and dissociation energies of UO₂X₄^2– → UO₂X₃^– + X^– are calculated, revealing that all gaseous dianions are in fact metastable. The dielectric constant of the environment is shown to be the key in controlling the thermodynamic and kinetic stabilities of the tetracoordinate uranyl complexes via modulation of the ligand–ligand Coulomb repulsions