Inspired by the recent discovery of the metal-centered tubular molecular rotor Cs B2-Ta@B18− with the record coordination number of CN = 20 and based on extensive first-principles theory calculations, we present herein the possibility of the largest tubular molecular rotors Cs B3-Ta@B18 (1) and C3v B4-Ta@B18+ (2) and smallest axially chiral endohedral metalloborospherenes D2 Ta@B22− (3 and 3′), unveiling a tubular-to-cage-like structural transition in metal-centered boron clusters at Ta@B22−via effective spherical coordination interactions. The highly stable Ta@B22− (3) as an elegant superatom, which features two equivalent corner-sharing B10 boron double chains interconnected by two B2 units with four equivalent B7 heptagons evenly distributed on the cage surface, conforms to the 18-electron configuration with a bonding pattern of σ + π double delocalization and follows the 2(n + 1)2 electron counting rule for spherical aromaticity (n = 2). Its calculated adiabatic detachment energy of ADE = 3.88 eV represents the electron affinity of the cage-like neutral D2 Ta@B22 which can be viewed as a superhalogen. The infrared, Raman, VCD, and UV-vis spectra of the concerned species are computationally simulated to facilitate their spectral characterizations.

Gold compounds, clusters, and nanoparticles are widely used as catalysts and therapeutic medicines; the interactions between gold and its ligands in these systems play important roles in their chemical properties and functionalities. In order to elucidate the nature of the chemical interactions between Au(I) and its ligands, herein we use several theoretical methods to study the chemical bonding in a variety of linear [AuX2]− complexes, where X = halogen atoms (F, Cl, Br, I, At and Uus), H, OH, SH, OCH3, SCH3, CN and SCN. It is shown that the most important bonding orbitals in these systems have significant contributions from the Au sd hybridized atomic orbitals. The ubiquitous linear or quasi-linear structures of [AuX2]− are attributed to the well-balanced optimal overlap in both σ and π bonding orbitals and minimal repulsion between the two negatively charged ligands. The stability of these complexes is related to the covalency of the Au–X bond and a periodic trend is found in the evolution of covalency along the halogen group ligands. The special stability of [Au(CN)2]− is a result of strong covalent and ionic interactions. For the superheavy element Uus, the covalency of Au–Uus is enhanced through the spin–orbit interactions.

Supported noble metal nanoparticles (including nanoclusters) are widely used in many industrial catalytic processes. While the finely dispersed nanostructures are highly active, they are usually thermodynamically unstable and tend to aggregate or sinter at elevated temperatures. This scenario is particularly true for supported nanogold catalysts because the gold nanostructures are easily sintered at high temperatures, under reaction conditions, or even during storage at ambient temperature. Here, we demonstrate that isolated Au single atoms dispersed on iron oxide nanocrystallites (Au1/FeOx) are much more sinteringresistant than Au nanostructures, and exhibit extremely high reaction stability for CO oxidation in a wide temperature range. Theoretical studies revealed that the positively charged and surface-anchored Au1 atoms with high valent states formed significant covalent metal-support interactions (CMSIs), thus providing the ultra-stability and remarkable catalytic performance. This work may provide insights and a new avenue for fabricating supported Au catalysts with ultra-high stability.

Combined anion photoelectron spectroscopy and relativistic quantum chemical studies are conducted on nucleobase–Au2− cluster anions. The vertical detachment energies of uracil–Au2− (UAu2−), thymine–Au2− (TAu2−), cytosine–Au2− (CAu2−), adenine–Au2− (AAu2−), guanine–Au2− (GAu2−) are determined to be 2.71 ± 0.08 eV, 2.74 ± 0.08 eV, 2.67 ± 0.08 eV, 2.65 ± 0.08 eV and 2.73 ± 0.08 eV, respectively, based on the measured photoelectron spectra. Through computational geometry optimizations we have identified the lowest-energy structures of these nucleobase–Au2− cluster anions. The structures are further confirmed by comparison of theoretically calculated vertical and adiabatic electron detachment energies with experimental measurements. The results reveal that the Au2− anion remains as an intact unit and interacts with the nucleobases through N–H⋯Au or C–H⋯Au nonconventional hydrogen bonds. The nucleobase–Au2− cluster anions have relatively weak N–H⋯Au hydrogen bonds and strong C–H⋯Au hydrogen bonds compared to those of nucleobase–Au− anions.

To understand the catalytic mechanism of alcohol oxidation with molecular oxygen on bulk metallic gold catalysts, we have systematically studied the oxidative dehydrogenation of methanol on Au(111) using density functional theory. It is found that molecular oxygen can be activated via a hydroperoxyl (OOH) intermediate produced by abstracting a hydrogen atom from co-adsorbed methanol or water. Interestingly, extra water molecules significantly promote the hydrogen-transfer reactions between CH3OH···O2 and H2O···O2 co-adsorbates, lowering the activation barrier of OOH formation from ∼0.90 to ∼0.45 eV. The formed OOH intermediate either directly reacts with methanol to produce formaldehyde or dissociates into adsorbed atomic oxygen and hydroxyl. Further calculations demonstrate that the oxidative dehydrogenation of methanol by OOH, atomic oxygen, and hydroxyl is extremely facile with low barriers between 0.06 and 0.30 eV. These results provide an explanation for the activation mechanism of molecular oxygen on bulk gold and reveal a possible pathway for alcohol oxidation with dioxygen.Keywords: bulk gold; density functional theory; hydroperoxyl; methanol oxidation; O2 activation; water

The tetraoxo pertechnetate anion (TcO4–) is of great interest for nuclear waste management and radiopharmceuticals. To elucidate its electronic structure and to compare with that of its lighter congener MnO4–, the photoelectron and electronic absorption spectra of MnO4– and TcO4– are investigated with density functional theory (DFT) and ab initio wave function theory (WFT). The vertical electron detachment energies (VDEs) of MnO4– obtained with the CR-EOM-CCSD(T) method are in good agreement with the lowest two experimental VDEs; the differences are less than 0.1 eV, representing a significant improvement over the IP-EOM-CCSD(T) result in the literature. Combining our CCSD(T) and CR-EOM-CCSD(T) results, the first five VDEs of TcO4– are estimated between 5 and 10 eV with an estimated accuracy of about ±0.2 eV. The vertical excitation energies are determined by using TD-DFT, CR-EOM-CCSD(T), and RAS-PT2 methods. The excitation energies and the assignments of the spectra are analyzed and partly improved. They are compared with reported SAC-CI results and available experimental data. Both dynamic and nondynamic electron correlations are important in the ground and excited states of MnO4– and TcO4–. Nondynamical correlations are particularly relevant in TcO4– for reliable prediction of excitation energies. In TcO4– one Rydberg state interlaces but does not mix with the valence excited states, and it disappears in the condensed phase.

While uranyl halide complexes [UO2(halogen)n]2–n (n = 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 np lone pairs in the heavier halogen complexes. Extensive bonding analyses are carried out for UO2X3– as well as for the doubly charged tetracoordinate complexes (UO2X42–), 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 UO2X42– → 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.

In neutral chemical compounds, the highest known oxidation state of all elements in the Periodic Table is +VIII. While PuO4 is viewed as an exotic Pu(+VIII) complex, we have shown here that no stable electronic homologue of octavalent RuO4 and OsO4 exists for PuO4, even though Pu has the same number of eight valence electrons as Ru and Os. Using quantum chemical approaches at the levels of quasi-relativistic DFT, MP2, CCSD(T), and CASPT2, we find the ground state of PuO4 as a quintet 5C2v-(PuO2)+(O2)− complex with the leading valence configuration of an (f3)plutonyl(V) unit, loosely coupled to a superoxido (π*3)O2– ligand. This stable isomer is likely detectable as a transient species, while the previously suggested planar 1D4h-Pu(VIII)O4 isomer is only metastable. Through electronic structure analyses, the bonding and the oxidation states are explained and rationalized. We have predicted the characteristics of the electronic and vibrational spectra to assist future experimental identification of (PuO2)+(O2)− by IR, UV–vis, and ionization spectroscopy.

The selective extraction of minor actinides(III) from the lanthanides(III) is a key step for spent fuel reprocessing. Theoretical calculations of geometries, electronic structures, coordination complexion, and thermodynamic properties of the actinides are essential for understanding the separation mechanisms and relevant reactions. This article presents a critical review of theoretical studies on actinide systems involved in the An(III)/Ln(III) separation process. We summarize various theoretical methods for electronic and molecular scale modeling and simulations of actinide coordination systems. The complexing mechanisms between metal cations and organic ligands and the strategies for the design of novel ligands for separation are discussed as well.Highlights► We review recent advances in computational modeling and simulations on the An(III)/Ln(III) separation process. ► Various theoretical methods for electronic and molecular-scale modeling and simulations of actinide systems are summarized. ► The complexation between soft-donating ligands and An(III)/Ln(III) ions are explored. ► The strategies for design of novel organic ligands for separation are discussed.

Carbon is known to form single, double and triple bonds. An educated search led us to a novel view on the bonding of carbon in the triatomic uranium carbide oxide molecule CUO. When comparing various empirical properties and theoretical indices of a whole set of related species, some of those molecules are best described with carbon being quadruply bonded, with the ubiquitous one σ- and two π-bonds, plus a non-negligible, albeit weak, rearward σ-bond. Observable indicators of bond strength suggest a rather high C–U bond order, significantly above three for a series of CUE molecules with different electrophilic ligands E. Several orbital-based indices count only a little more than three C–U bonds, although with additional ionic bonding. The bonding in the CU unit of CUE differs from the recently claimed quadruple bonding in C2 owing to the rich U-pfds valence shell. CUE molecules are comparatively stable units with a high nucleophilicity at the carbon end, and they may become chemically interesting intermediates, for instance in water decomposition reactions.

Bare uranyl tetrafluoride (UO2F42−) and its solvation complexes by one and two water or acetonitrile molecules have been observed in the gas phase using electrospray ionization and investigated by photoelectron spectroscopy and ab initio calculations. The isolated UO2F42− dianion is found to be electronically stable with an adiabatic electron binding energy of 1.10 ± 0.05 eV and a repulsive Coulomb barrier of ∼2 eV. Photoelectron spectra of UO2F42− display congested features due to detachment from U–O bonding orbitals and F 2p lone pairs. Solvated complexes by H2O and CH3CN, UO2F4(H2O)n2− and UO2F4(CH3CN)n2− (n = 1, 2), are also observed and their photoelectron spectra are similar to those of the bare UO2F42− dianion, suggesting that the solvent molecules are coordinated to the outer sphere of UO2F42− with relatively weak interactions between the solvent molecules and the dianion core. Both DFT and CCSD(T) calculations are performed on UO2F42− and its solvated species to understand the electronic structure of the dianion core and solute–solvent interactions. The strong U–F interactions with partial (d–p)π bonding are shown to weaken the UO bonds in the [OUO]2+ unit. Each H atom in the water molecules forms a H-bond to a F atom in the equatorial plane of UO2F42−, while each CH3CN molecule forms three H-bonds to two F ligands and one axial oxygen.

We report an investigation of the electronic structure and chemical bonding of AuH2− using photoelectron spectroscopy and ab initio calculations. We obtained vibrationally resolved photoelectron spectra of AuH2− at several photon energies. Six electronic states of AuH2 were observed and assigned according to the theoretical calculations. The ground state of AuH2− is known to be linear, while that of neutral AuH2 is bent with a ∠H–Au–H equilibrium bond angle of 129°. This large geometry change results in a very broad bending vibrational progression in the photoelectron spectra for the ground-state transition. The electron affinity of AuH2 is measured to be 3.030 ± 0.020 eV. A short bending vibrational progression is also observed in the second photodetachment band, suggesting a slightly bent structure for the first excited state of AuH2. The linear geometry is a saddle point for the ground and first excited states of AuH2, resulting in double-well potentials for these states along the bending coordinate. Spectroscopic evidence is observed for the detachment transitions to the double-well potentials of the ground and first excited states of AuH2. Higher excited states of AuH2 due to detachment from the nonbonding Au 5d electrons are all linear, similar to the anion ground state. Kohn–Sham molecular orbital analyses reveal surprising participation of H 2p orbitals in the Au–H chemical bonding and an unprecedented weak Au 5dπ to H 2pπ back donation. The simplicity of the linear AuH2− anion and its novel spectroscopic features make it a textbook example for understanding the covalent bonding properties and relativistic effects of Au.

The reactions of Group-3 metal atoms with carbon monoxide in solid argon have been studied using matrix isolation infrared absorption spectroscopy. The lanthanide monocarbonyls LnCO were produced spontaneously on annealing. The observations on LnCO, Ln = Pr, Nd, Sm, Eu, Tb, Dy, Ho, and Er are new. We also theoretically study the structure, bonding, and C–O stretch infrared frequencies. The covalent M–C bonding contains both M ← C σ donation from the carbon lone pair, and M 5d → CO 2π* back donation contributions. In addition to the open 4fn shells, the total spin, as found earlier, may have contributions from an M ‘σ doughnut’ and the M–C π bond, in a σ1π1, σ1π2 high-spin, or σ2π1 low-spin configuration. They form at least a single-bond, and those with the σ1π2 configuration approach a double bond in length. The weakening of the C–O bonding is related to the back donation to the antibonding C–O 2π* orbital.

Electronic states and spectra of NpO22+ and NpO2Cl42– with a Np 5f1 ground-state configuration, related to low-lying 5f–5f and ligand-to-metal charge-transfer (CT) transitions, are investigated, using restricted-active-space perturbation theory (RASPT2) with spin–orbit coupling. Restrictions on the antibonding orbital occupations have little influence on the 5f–5f transition energies, but an important impact on the CT states with an open bonding orbital shell. The present calculations provide significant improvement over previous literature results. The assignment of the experimental electronic spectra of Cs2NpO2Cl4 is refined, based on our calculations of NpO2Cl42–. Assignments on the basis of bare NpO22+ are less reliable, since the equatorial Cl ligands perturb the excited-state energies considerably. Calculated changes of the Np–O bond lengths are in agreement with the observed short symmetric-stretching progressions in the f–f spectra and longer progressions in the CT spectra of neptunyl. A possible luminescence spectrum of the lowest quartet CT state is predicted.

The change ΔRx of bond length Rx for atom X in a molecule upon electronic transition can be derived from the intensities Ii of the vibrational stretching progression v = 0 → i of the electronic absorption or emission spectrum. In many cases, a simple model is sufficient for a reasonable estimate of ΔRx. For symmetric molecules, however, conceptual problems in the literature of many decades are evident. The breathing modes of various types of symmetric molecules Xn and AXn (A at the center) are here discussed. In the simplest case of a harmonic vibration of the same mode in the initial and final electronic states, we obtain ΔRx ≈ [2S/(ωmx)]1/2/w1/2 (all quantities in atomic units). ω and S are respectively the observed vibrational quanta and the Huang–Rhys factor (corresponding, e.g., to the vibrational intensity ratio I1/I0 ≈ S), mx is the mass of vibrating atom X, and w is a topological factor for molecule Xn or AXn. The factor 1/w1/2 in the expression for ΔRx must not be neglected. The spectra and bond length changes of several symmetric molecules AXn and Xn are discussed. The experimental bond length changes correctly derived with factor 1/w1/2 are verified by reliable quantum chemical calculations.

Highly dispersed and well-homogenized Au–Pd alloy nanoparticles with average particle sizes of ∼2 nm and tunable Au/Pd ratios were prepared by an adsorption–reduction method on the amine-functionalized SBA-15 support. The chemisorptions of H2 and CO as well as the IR spectra of CO adsorption show that with increase of the Au/Pd ratios the surface Pd atoms are separated by gold atoms gradually until totally isolated at Au/Pd ≥ 0.95, which indicates the formation of Pd single atoms at higher Au/Pd ratios. The chemisorption of O2 shows that both the adsorption heat and the saturation uptake decrease with an increase of Au/Pd ratio, suggesting alloying Pd with gold will facilitate the desorption of oxygen adatoms as O2, which is generally the rate-determining step for N2O decomposition reaction. Theoretical investigations using periodic DFT methods confirm the tunable O2 desorption ability by alloying Pd with Au and indicate that contiguously located Pd sites are indispensable for N2O decomposition because they function as the active sites for the elementary step of N2O decomposition into N2 and oxygen adatom, which becomes the rate-determining step over the Au–Pd alloy catalysts.

We report a combined experimental and theoretical investigation of [XAuCN]− (X = F, Cl, Br, I) to examine the chemical bonding in the mixed cyanide halide Au(I) complexes. Photoelectron spectra are obtained for [XAuCN]−, yielding electron affinities of 5.38 ± 0.05, 5.14 ± 0.05, and 4.75 ± 0.05 eV for XAuCN (X = Cl, Br, I), respectively. Relativistic quantum chemical calculations based on wavefunction theory and density functional theory are carried out to help interpret the photoelectron spectra and elucidate the electronic structures and chemical bonding in the [XAuCN]− complexes. Spin–orbit coupling is found to be important in all the complexes, quenching the Renner–Teller distortion in the neutral molecules. Ab initio calculations including spin–orbit effects allow quantitative assignments of the observed photoelectron spectra. A variety of chemical bonding analyses based on the charge population, bond orders, and electron localization functions have been carried out, revealing a gradual transition from ionic behavior between F–Au in [FAuCN]− to relatively strong covalent bonding between I–Au in [IAuCN]−. Both relativistic effects and electron correlations are shown to enhance the covalency in the gold iodide complex.

The electronic absorption and emission spectra of free UO2Cl2 and its Ar-coordinated complexes below 27 000 cm–1 are investigated at the levels of ab initio complete active space second-order perturbation theory (CASPT2) and coupled-cluster singles and doubles and perturbative triples [CCSD(T)] using valence 3ζ-polarized basis sets. The influence of the argon matrix in the 12K experiment on the electronic spectra is explored by investigating the excited states of argon complexes ArnUO2Cl2. The calculated two most stable complexes with n = 2, 3 can explain the observed two matrix sites corresponding to the experimental two-component luminescence decay. In these uranyl complexes, Ar-coordination is found to have little influence on the 3Φ (Ω = 2g) character of the luminescent state and on the electronic spectral shape. The calculations yield a coherent assignment of the experimental excitation spectra that improves on previous assignments. The simulated luminescence spectral curves based on the calculated spectral parameters of UO2Cl2 from both CASPT2 and CCSD(T) agree well with experiment.

Uranium hexafluoride (UF6) is an important compound in nuclear chemistry. The theoretical investigation of its excited states is difficult due to the large number of uranium valence orbitals and ligand lone pairs. We report here a detailed relativistic quantum chemical investigation of its excited states up to about 10 eV using restricted active space second-order perturbation theory (RASPT2). Scalar and spin–orbit (SO) relativistic effects are treated by a relativistic small-core pseudopotential. The RASPT2/SO results remain moderately accurate when the electrons in the active space are restricted to single and double excitations. All eight major spectral peaks corresponding to ligand-to-metal charge transfer have been reproduced within an accuracy of about 0.2 eV and are tentatively assigned. We find that BLYP-based hybrid density functional with 35% Hartree–Fock exchange well reproduce the excitation energies of UF6.

The finding of the periodic law is a milestone in chemical science. The periodicity of light elements in the Periodic Table is fully accounted for by quantum mechanics. Here we report that relativistic effects change the bond multiplicity of the group 6 diatomic molecules M2 (M = Cr, Mo, W, Sg) from hextuple bonds for Cr2, Mo2, W2 to quadruple bonds for Sg2, thus breaking the periodicity in the nonrelativistic domain. The same trend is also found for other superheavy-element diatomics Rf2, Db2, Bh2, and Hs2.

We report an investigation of the electronic structure and chemical bonding of AuH2− using photoelectron spectroscopy and ab initio calculations. We obtained vibrationally resolved photoelectron spectra of AuH2− at several photon energies. Six electronic states of AuH2 were observed and assigned according to the theoretical calculations. The ground state of AuH2− is known to be linear, while that of neutral AuH2 is bent with a ∠H–Au–H equilibrium bond angle of 129°. This large geometry change results in a very broad bending vibrational progression in the photoelectron spectra for the ground-state transition. The electron affinity of AuH2 is measured to be 3.030 ± 0.020 eV. A short bending vibrational progression is also observed in the second photodetachment band, suggesting a slightly bent structure for the first excited state of AuH2. The linear geometry is a saddle point for the ground and first excited states of AuH2, resulting in double-well potentials for these states along the bending coordinate. Spectroscopic evidence is observed for the detachment transitions to the double-well potentials of the ground and first excited states of AuH2. Higher excited states of AuH2 due to detachment from the nonbonding Au 5d electrons are all linear, similar to the anion ground state. Kohn–Sham molecular orbital analyses reveal surprising participation of H 2p orbitals in the Au–H chemical bonding and an unprecedented weak Au 5dπ to H 2pπ back donation. The simplicity of the linear AuH2− anion and its novel spectroscopic features make it a textbook example for understanding the covalent bonding properties and relativistic effects of Au.

Carbon is known to form single, double and triple bonds. An educated search led us to a novel view on the bonding of carbon in the triatomic uranium carbide oxide molecule CUO. When comparing various empirical properties and theoretical indices of a whole set of related species, some of those molecules are best described with carbon being quadruply bonded, with the ubiquitous one σ- and two π-bonds, plus a non-negligible, albeit weak, rearward σ-bond. Observable indicators of bond strength suggest a rather high C–U bond order, significantly above three for a series of CUE molecules with different electrophilic ligands E. Several orbital-based indices count only a little more than three C–U bonds, although with additional ionic bonding. The bonding in the CU unit of CUE differs from the recently claimed quadruple bonding in C2 owing to the rich U-pfds valence shell. CUE molecules are comparatively stable units with a high nucleophilicity at the carbon end, and they may become chemically interesting intermediates, for instance in water decomposition reactions.

The reactions of Group-3 metal atoms with carbon monoxide in solid argon have been studied using matrix isolation infrared absorption spectroscopy. The lanthanide monocarbonyls LnCO were produced spontaneously on annealing. The observations on LnCO, Ln = Pr, Nd, Sm, Eu, Tb, Dy, Ho, and Er are new. We also theoretically study the structure, bonding, and C–O stretch infrared frequencies. The covalent M–C bonding contains both M ← C σ donation from the carbon lone pair, and M 5d → CO 2π* back donation contributions. In addition to the open 4fn shells, the total spin, as found earlier, may have contributions from an M ‘σ doughnut’ and the M–C π bond, in a σ1π1, σ1π2 high-spin, or σ2π1 low-spin configuration. They form at least a single-bond, and those with the σ1π2 configuration approach a double bond in length. The weakening of the C–O bonding is related to the back donation to the antibonding C–O 2π* orbital.

We report a combined experimental and theoretical investigation of [XAuCN]− (X = F, Cl, Br, I) to examine the chemical bonding in the mixed cyanide halide Au(I) complexes. Photoelectron spectra are obtained for [XAuCN]−, yielding electron affinities of 5.38 ± 0.05, 5.14 ± 0.05, and 4.75 ± 0.05 eV for XAuCN (X = Cl, Br, I), respectively. Relativistic quantum chemical calculations based on wavefunction theory and density functional theory are carried out to help interpret the photoelectron spectra and elucidate the electronic structures and chemical bonding in the [XAuCN]− complexes. Spin–orbit coupling is found to be important in all the complexes, quenching the Renner–Teller distortion in the neutral molecules. Ab initio calculations including spin–orbit effects allow quantitative assignments of the observed photoelectron spectra. A variety of chemical bonding analyses based on the charge population, bond orders, and electron localization functions have been carried out, revealing a gradual transition from ionic behavior between F–Au in [FAuCN]− to relatively strong covalent bonding between I–Au in [IAuCN]−. Both relativistic effects and electron correlations are shown to enhance the covalency in the gold iodide complex.

Bare uranyl tetrafluoride (UO2F42−) and its solvation complexes by one and two water or acetonitrile molecules have been observed in the gas phase using electrospray ionization and investigated by photoelectron spectroscopy and ab initio calculations. The isolated UO2F42− dianion is found to be electronically stable with an adiabatic electron binding energy of 1.10 ± 0.05 eV and a repulsive Coulomb barrier of ∼2 eV. Photoelectron spectra of UO2F42− display congested features due to detachment from U–O bonding orbitals and F 2p lone pairs. Solvated complexes by H2O and CH3CN, UO2F4(H2O)n2− and UO2F4(CH3CN)n2− (n = 1, 2), are also observed and their photoelectron spectra are similar to those of the bare UO2F42− dianion, suggesting that the solvent molecules are coordinated to the outer sphere of UO2F42− with relatively weak interactions between the solvent molecules and the dianion core. Both DFT and CCSD(T) calculations are performed on UO2F42− and its solvated species to understand the electronic structure of the dianion core and solute–solvent interactions. The strong U–F interactions with partial (d–p)π bonding are shown to weaken the UO bonds in the [OUO]2+ unit. Each H atom in the water molecules forms a H-bond to a F atom in the equatorial plane of UO2F42−, while each CH3CN molecule forms three H-bonds to two F ligands and one axial oxygen.

Combined anion photoelectron spectroscopy and relativistic quantum chemical studies are conducted on nucleobase–Au2− cluster anions. The vertical detachment energies of uracil–Au2− (UAu2−), thymine–Au2− (TAu2−), cytosine–Au2− (CAu2−), adenine–Au2− (AAu2−), guanine–Au2− (GAu2−) are determined to be 2.71 ± 0.08 eV, 2.74 ± 0.08 eV, 2.67 ± 0.08 eV, 2.65 ± 0.08 eV and 2.73 ± 0.08 eV, respectively, based on the measured photoelectron spectra. Through computational geometry optimizations we have identified the lowest-energy structures of these nucleobase–Au2− cluster anions. The structures are further confirmed by comparison of theoretically calculated vertical and adiabatic electron detachment energies with experimental measurements. The results reveal that the Au2− anion remains as an intact unit and interacts with the nucleobases through N–H⋯Au or C–H⋯Au nonconventional hydrogen bonds. The nucleobase–Au2− cluster anions have relatively weak N–H⋯Au hydrogen bonds and strong C–H⋯Au hydrogen bonds compared to those of nucleobase–Au− anions.

Gold compounds, clusters, and nanoparticles are widely used as catalysts and therapeutic medicines; the interactions between gold and its ligands in these systems play important roles in their chemical properties and functionalities. In order to elucidate the nature of the chemical interactions between Au(I) and its ligands, herein we use several theoretical methods to study the chemical bonding in a variety of linear [AuX2]− complexes, where X = halogen atoms (F, Cl, Br, I, At and Uus), H, OH, SH, OCH3, SCH3, CN and SCN. It is shown that the most important bonding orbitals in these systems have significant contributions from the Au sd hybridized atomic orbitals. The ubiquitous linear or quasi-linear structures of [AuX2]− are attributed to the well-balanced optimal overlap in both σ and π bonding orbitals and minimal repulsion between the two negatively charged ligands. The stability of these complexes is related to the covalency of the Au–X bond and a periodic trend is found in the evolution of covalency along the halogen group ligands. The special stability of [Au(CN)2]− is a result of strong covalent and ionic interactions. For the superheavy element Uus, the covalency of Au–Uus is enhanced through the spin–orbit interactions.