Hydrolysis of Metal Dioxides Differentiates d-block from f-block Elements: Pa(V) as a 6d Transition Metal; Pr(V) as a 4f "Lanthanyl".

Gas-phase reactions of pentavalent metal dioxide cations MO with water were studied experimentally for M = V, Nb, Ta, Pr, Pa, U, Pu, and Am. Addition of two HO can occur by adsorption to yield hydrate (HO)MO or by hydrolysis to yield hydroxide M(OH). Displacement of HO by acetone indicates hydrates for Pr, U, Pu, and Am, whereas nondisplacement indicates hydroxides for Nb, Ta, and Pa.

Coordination of 2,2'-(Trifluoroazanediyl)bis(,'-dimethylacetamide) with U(VI), Nd(III), and Np(V): A Thermodynamic and Structural Study.

Thermodynamic properties of the complexation of 2,2'-(trifluoroazanediyl)bis(,'-dimethylacetamide) (CFABDMA) with U(VI), Nd(III), and Np(V) have been studied in 1.0 M NaNO at 25 °C. Equilibrium constants of the complexation were determined by potentiometry and spectrophotometry.

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, AnO 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, PaO and UO, but not the next two, NpO and PuO. The An-O bond dissociation energies (BDEs) decrease from PaO to PuO, such that the observation of a parallel decrease in the An-O bond reactivity is intriguing.

Pentavalent Curium, Berkelium, and Californium in Nitrate Complexes: Extending Actinide Chemistry and Oxidation States.

Pentavalent actinyl nitrate complexes AnO(NO) were produced by elimination of two NO from An(NO) for An = Pu, Am, Cm, Bk, and Cf. Density functional theory (B3LYP) and relativistic multireference (CASPT2) calculations confirmed the AnO(NO) as AnO actinyl moieties coordinated by nitrates. Computations of alternative AnO(NO) and AnO(NO) revealed significantly higher energies.

Thermodynamic, Structural, and Computational Investigation on the Complexation between UO and Amine-Functionalized Diacetamide Ligands in Aqueous Solution.

The stability constants (log β), enthalpies of complexation (ΔH), and entropies of complexation (ΔS) for the complexes of uranium(VI) with a series of amine-functionalized diaetamide ligands, 2,2'-benzylazanediylbis(N,N'-dimethylacetamide) (BnABDMA), 2,2'-azanediylbis(N,N'-dimethylacetamide) (ABDMA), and 2,2'-methylazanediylbis(N,N'-dimethylacetamide) (MABDMA), in aqueous solution were determined by potentiometry and calorimetry. Electronspray ionization mass spectrometry was used to verify the presence of uranium(VI) complexes in solution. The thermodynamic data indicate that the binding strengths of the three ligands with UO follow the order BnABDMA < ABDMA < MABDMA, parallel to the order of the protonation constants as well as the order of the stability of the Nd complexes, suggesting that the complexation of UO with the ligands consist predominantly of electrostatic interactions.

Heptavalent Actinide Tetroxides NpO and PuO: Oxidation of Pu(V) to Pu(VII) by Adding an Electron to PuO.

The highest known actinide oxidation states are Np(VII) and Pu(VII), both of which have been identified in solution and solid compounds. Recently a molecular Np(VII) complex, NpO(NO), was prepared and characterized in the gas phase. In accord with the lower stability of heptavalent Pu, no Pu(VII) molecular species has been identified.

Remarkably High Stability of Late Actinide Dioxide Cations: Extending Chemistry to Pentavalent Berkelium and Californium.

Actinyl chemistry is extended beyond Cm to BkO and CfO through transfer of an O atom from NO to BkO or CfO , establishing a surprisingly high lower limit of 73 kcal mol for the dissociation energies, D[O-(BkO )] and D[O-(CfO )]. CCSD(T) computations are in accord with the observed reactions, and characterize the newly observed dioxide ions as linear pentavalent actinyls; these being the first Bk and Cf species with oxidation states above IV. Computations of actinide dioxide cations AnO for An=Pa to Lr reveal an unexpected minimum for D[O-(CmO )].

Cleaving Off Uranyl Oxygens through Chelation: A Mechanistic Study in the Gas Phase.

Recent efforts to activate the strong uranium-oxygen bonds in the dioxo uranyl cation have been limited to single oxo-group activation through either uranyl reduction and functionalization in solution, or by collision induced dissociation (CID) in the gas-phase, using mass spectrometry (MS). Here, we report and investigate the surprising double activation of uranyl by an organic ligand, 3,4,3-LI(CAM), leading to the formation of a formal U chelate in the gas-phase. The cleavage of both uranyl oxo bonds was experimentally evidenced by CID, using deuterium and O isotopic substitutions, and by infrared multiple photon dissociation (IRMPD) spectroscopy.

A Uranyl Peroxide Dimer in the Gas Phase.

The gas-phase uranyl peroxide dimer, [(UO)(O)(L)] where L = 2,2'-trifluoroethylazanediyl)bis(N,N'-dimethylacetamide), was synthesized by electrospray ionization of a solution of UO and L. Collision-induced dissociation of this dimer resulted in endothermic O atom elimination to give [(UO)(O)(L)], which was found to spontaneously react with water via exothermic hydrolytic chemisorption to yield [(UO)(OH)(L)]. Density functional theory computations of the energies for the gas-phase reactions are in accord with observations.

Heptavalent Neptunium in a Gas-Phase Complex: (NpO)(NO).

A central goal of chemistry is to achieve ultimate oxidation states, including in gas-phase complexes with no condensed phase perturbations. In the case of the actinide elements, the highest established oxidation states are labile Pu(VII) and somewhat more stable Np(VII). We have synthesized and characterized gas-phase AnO(NO) complexes for An = U, Np, and Pu by endothermic NO elimination from AnO(NO).

Divalent and trivalent gas-phase coordination complexes of californium: evaluating the stability of Cf(ii).

The divalent oxidation state is increasingly stable relative to the trivalent state for the later actinide elements, with californium the first actinide to exhibit divalent chemistry under moderate conditions. Although there is evidence for divalent Cf in solution and solid compounds, there are no reports of discrete complexes in which Cf(II) is coordinated by anionic ligands. Described here is the divalent Cf methanesulfinate coordination complex, Cf(II)(CH3SO2)3(-), prepared in the gas phase by reductive elimination of CH3SO2 from Cf(III)(CH3SO2)4(-).

Thermodynamic study of the complexation between Nd(3+) and functionalized diacetamide ligands in solution.

A series of amine functionalized ligands, including 2,2'-(benzylazanediyl)bis(N,N'-dimethylacetamide) (BnABDMA), 2,2'-azanediylbis(N,N'-dimethylacetamide) (ABDMA), and 2,2'-(methylazanediyl)bis(N,N'-dimethylacetamide) (MABDMA), are synthesized for the thermodynamic study of their complexation with Nd(3+) ions. Their complexation in solution is investigated using potentiometry, spectrophotometry, calorimetry, and electrospray ionization mass spectrometry. The results suggest that these ligands act as tridentate ligands.

Activation of carbon dioxide by a terminal uranium-nitrogen bond in the gas-phase: a demonstration of the principle of microscopic reversibility.

Activation of CO2 is demonstrated by its spontaneous dissociative reaction with the gas-phase anion complex NUOCl2(-), which can be considered as NUO(+) coordinated by two chloride anion ligands. This reaction was previously predicted by density functional theory to occur exothermically, without barriers above the reactant energy. The present results demonstrate the validity of the prediction of microscopic reversibility, and provide a rare case of spontaneous dissociative addition of CO2 to a gas-phase complex.

Oxidation of Actinyl(V) Complexes by the Addition of Nitrogen Dioxide Is Revealed via the Replacement of Acetate by Nitrite.

The gas-phase complexes AnO2(CH3CO2)2(-) are actinyl(V) cores, An(V)O2(+) (An = U, Np, Pu), coordinated by two acetate anion ligands. Whereas the addition of O2 to U(V)O2(CH3CO2)2(-) exothermically produces the superoxide complex U(VI)O2(O2)(CH3CO2)2(-), this oxidation does not occur for Np(V)O2(CH3CO2)2(-) or Pu(V)O2(CH3CO2)2(-) because of the higher reduction potentials for Np(V) and Pu(V). It is demonstrated that NO2 is a more effective electron-withdrawing oxidant than O2, with the result that all three An(V)O2(CH3CO2)2(-) exothermically react with NO2 to form nitrite complexes, An(VI)O2(CH3CO2)2(NO2)(-).

Vibrational State-Selective Resonant Two-Photon Photoelectron Spectroscopy of AuS(-) via a Spin-Forbidden Excited State.

Vibrational state-selective resonant two-photon photoelectron spectra have been obtained via a triplet intermediate state ((3)Σ(-)) of AuS(-) near its detachment threshold using high-resolution photoelectron imaging of cryogenically cooled AuS(-) anions. Four vibrational levels of the (3)Σ(-) excited state are observed to be below the detachment threshold. Resonant two-photon absorptions through these levels yield vibrational state-selective photoelectron spectra to the (2)Σ final state of neutral AuS with broad and drastically different Franck-Condon distributions, reflecting the symmetries of the vibrational wave functions of the (3)Σ(-) intermediate state.

Photoelectron spectroscopy and theoretical studies of gaseous uranium hexachlorides in different oxidation states: UCl6 (q-) (q = 0-2).

Uranium chlorides are important in actinide chemistry and nuclear industries, but their chemical bonding and many physical and chemical properties are not well understood yet. Here, we report the first experimental observation of two gaseous uranium hexachloride anions, UCl6 (-) and UCl6 (2-), which are probed by photoelectron spectroscopy in conjunction with quantum chemistry calculations. The electron affinity of UCl6 is measured for the first time as +5.

Halide abstraction from halogenated acetate ligands by actinyls: a competition between bond breaking and bond making.

Transfer of halogen atoms from halogenated acetate ligands, CX3CO2 (X = F, Cl, Br), to actinyls, AnO2(2+) (An = U, Np, Pu) is stimulated by collision-induced dissociation (CID) in a quadrupole ion trap. CID of [AnO2(CF3CO2)3](-) complexes results exclusively in F atom transfer, concomitant with elimination of CF2CO2, to produce [(CF3CO2)2AnO2F](-), [(CF3CO2)AnO2F2](-), and [AnO2F3](-). This contrasts with CID of transition metal fluoroacetates for which CO2-elimination to produce organometallics is an important pathway, a disparity that can be attributed to the differing bond dissociation energies (BDEs) of the created metal-carbon and metal-fluorine bonds.

Binding of pyrazine-functionalized calix[4]arene ligands with lanthanides in an ionic liquid: thermodynamics and coordination modes.

The complexation of representative lanthanides with three calix[4]arenes functionalized with four pyrazine pendent arms containing different substituents such as carbamoyl dioctyl (), diisopropyl phosphonate (), and diphenyl phosphoryl () was investigated in water-saturated 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BumimTf2N) by absorption spectroscopy, luminescence spectroscopy, and microcalorimetry. All three ligands form 1 : 1 ML complexes (M = Eu(3+) and L = ligand), and the stability constants (log β) follow the order: (-1.38 ± 0.

High-resolution photoelectron imaging of cold C₆₀⁻ anions and accurate determination of the electron affinity of C₆₀.

High-resolution photoelectron imaging and spectroscopy of cold C₆₀⁻ anions are reported using a newly built photoelectron imaging apparatus coupled with an electrospray ionization source and a temperature-controlled cryogenic ion trap. Vibrationally resolved photoelectron spectra are obtained for the detachment transition from the ground state of C₆₀⁻ to that of C60 at various detachment wavelengths from 354.84 nm to 461.

Assessment of Quantum Mechanical Methods for Copper and Iron Complexes by Photoelectron Spectroscopy.

Broken-symmetry density functional theory (BS-DFT) calculations are assessed for redox energetics [Cu(SCH)], [Cu(NCS)], [FeCl], and [Fe(SCH)] against vertical detachment energies (VDE) from valence photoelectron spectroscopy (PES), as a prelude to studies of metalloprotein analogs. The M06 and B3LYP hybrid functionals give VDE that agree with the PES VDE for the Fe complexes, but both underestimate it by ∼400 meV for the Cu complexes; other hybrid functionals give VDEs that are an increasing function of the amount of Hartree-Fock (HF) exchange and so cannot show good agreement for both Cu and Fe complexes. Range-separated (RS) functionals appear to give a better distribution of HF exchange since the negative HOMO energy is approximately equal to the VDEs but also give VDEs dependent on the amount of HF exchange, sometimes leading to ground states with incorrect electron configurations; the LRC-PBEh functional reduced to 10% HF exchange at short-range give somewhat better values for both, although still ∼150 meV too low for the Cu complexes and ∼50 meV too high for the Fe complexes.

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.

A joint photoelectron spectroscopy and theoretical study on the electronic structure of UCl5- and UCl5.

We report a combined photoelectron spectroscopic and relativistic quantum chemistry study on gaseous UCl5(-) and UCl5. The UCl5(-) anion is produced using electrospray ionization and found to be highly electronically stable with an adiabatic electron binding energy of 4.76±0.