Fourier transform ion cyclotron resonance mass spectrometry was employed to study the products and kinetics of gas-phase reactions of Cm+ and Cm2+; parallel studies were carried out with La+/2+, Gd+/2+ and Lu+/2+. Reactions with oxygen-donor molecules provided estimates for the bond dissociation energies, D[M+-O] (M = Cm, Gd, Lu). The first ionization energy, IE[CmO], was obtained from the reactivity of CmO+ with dienes, and the second ionization energies, IE[MO+] (M = Cm, La, Gd, Lu), from the rates of electron-transfer reactions from neutrals to the MO2+ ions. The following thermodynamic quantities for curium oxide molecules were obtained: IE[CmO] = 6.4+-0.2 eV; IE[CmO+] = 15.8+-0.4 eV; D[Cm-O] = 710+-45 kJ mol-1; D[Cm+-O] = 670+-40 kJ mol-1; and D[Cm2+-O] = 342+-55 kJ mol-1. Estimates for the M2+-O bond energies for M = Cm, La, Gd and Lu are all intermediate between D[N2-O] and D[OC-O]--i.e., 167 kJ mol-1 < D[M2+-O] < 532 kJ mol-1 -- such that the four MO2+ ions fulfill the thermodynamic requirement for catalytic O-atom transport from N2O to CO. It was demonstrated that the kinetics are also favorable and that the CmO2+, LaO2+, GdO2+ and LuO2+ dipositive ions each catalyze the gas-phase oxidation of CO to CO2 by N2O. The CmO2+ ion appeared during the reaction of Cm+ with O2 when the intermediate, CmO+, was not collisionally cooled -- although its formation is kinetically and/or thermodynamically unfavorable, CmO2+ is a stable species.

The gas-phase reactivity of doubly-charged lanthanide cations, Ln2+ (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), with alkanes (methane, ethane, propane, n-butane) and alkenes (ethene, propene, 1-butene) was studied by Fourier transform ion cyclotron resonance mass spectrometry. The reaction products consisted of different combinations of doubly-charged organometallic ions?adducts or species formed via metal-ion-induced hydrogen, dihydrogen, alkyl, or alkane eliminations from the hydrocarbons?and singly-charged ions that resulted from electron, hydride, or methide transfers from the hydrocarbons to the metal ions. The only lanthanide cations capable of activating the hydrocarbons to form doubly-charged organometallic ions were La2+, Ce2+, Gd2+, and Tb2+, which have ground-state or low-lying d1 electronic configurations. Lu2+, with an accessible d1 electronic configuration but a rather high electron affinity, reacted only through transfer channels. The remaining Ln2+ reacted via transfer channels or adduct formation. The different accessibilities of d1 electronic configurations and the range of electron affinities of the Ln2+ cations allowed for a detailed analysis of the trends for metal(2+) reactivity and the conditions for occurrence of bond activation, adduct formation, and electron, hydride, and methide transfers.

The ground and excited states of neutral and cationic PuO and PuO2 have been studied with multiconfigurational quantum chemical methods followed by second order perturbation theory, the CASSCF/CASPT2 method. Scalar relativistic effects and spin-orbit coupling have been included in the treatment. As literature values for the ionization energy of PuO2 are in the wide range of ~;;6.6 eV to ~;;10.1 eV, a central goal of the computations was to resolve these discrepancies; the theoretical results indicate that the ionization energy is near the lower end of this range. The calculated ionization energies for PuO, PuO+ and PuO2+ are in good agreement with the experimental values.

Chapter 1. Motivations and techniques used for studying lanthanide-ligand bonding are presented. Lanthanides are critical materials that face significant challenges in their extraction and separation. The role of redox, covalency, and sterics in controlling lanthanide bond stability is summarized. Gas-phase methods are demonstrated as advantageous to probing reactive and unstable complexes, such as lanthanide complexes explored in this work. Mass spectrometers equipped with electrospray and ion traps are introduced as instruments with the ability to isolate, synthesize, and probe reactivity of novel lanthanide complexes, offering insight into the nature of lanthanide-ligand bonding for improving separations efforts.

Chapter 2. The gas-phase preparation, isolation, and reactivity of a series of lanthanide complexes featuring the elusive Ln(III)=O bond is reported. The [Ln(O)(X)2]– complexes (X = NO3– or CH3CO2–) are prepared from [Ln(CH3CO2)(X)3]– precursors through decarboxylation followed by either nitromethane or acetone elimination. The lanthanide-oxo complexes are all observed to hydrolyze, the rate being a measure of Ln(III)=O bond stability. Rates of hydrolysis for [Ln(O)(NO3)2]– are essentially invariant, whereas the rates of hydrolysis for [LnIII(O)(CH3CO2)2]– exhibit a moderate monotonic decrease across the lanthanide series. Reaction kinetics are discussed with respect to factors controlling f-element-oxo bond hydrolysis, such as participation of 5d2 electrons, changes in covalency via variations in 5d orbital energies and radial extensions, and steric crowding around the lanthanide centers. The fast hydrolysis rates and their lack of correlation to electronic and qualitative covalent considerations confirm the expected strong polarization in Ln(III)=O bonding, with variations in covalency having minimal impact on reactivity.

Chapter 3. The gas-phase preparation, isolation, and reactivity of lanthanide-oxide nitrate complexes [Ln(O)(NO3)3]–, featuring the LnO 2+ moiety, is reported. These complexes are prepared from [Ln(NO3)4]– precursors (Ln = Ce, Pr, Nd, Sm, Tb, Dy) through nitrate decomposition. The LnO 2+ moiety within [Ln(O)(NO3)3]– features a Ln(III)–O⦁ oxyl, Ln(IV)=O oxo, or intermediate Ln(III/IV) oxyl/oxo bond, depending on the accessibility of the tetravalent Ln(IV) state. The hydrogen atom abstraction reactivity of the LnO 2+ complexes to form unambiguously trivalent [Ln(OH)(NO3)3]– reveals the nature of the oxide bond. The result of slower reactivity of PrO 2+ versus TbO 2+ is considered to indicate higher stability of the tetravalent praseodymium-oxo, Pr(IV)=O, versus Tb(IV)=O. This is the first report of Pr(IV) as more stable than Tb(IV), which is discussed with respect to ionization potentials, standard electrode potentials, atomic promotion energies, and oxo bond covalency via 4f and/or 5d orbital participation.

Chapter 4. The gas-phase preparation, isolation, and reactivity of a series of organolanthanides featuring the Ln–CH3 bond is reported. The complexes are formed by decarboxylating anionic lanthanide acetates to form trivalent [Ln(CH3)(CH3CO2)3]–, divalent [Eu(CH3)(CH3CO2)2]–, and the first examples of tetravalent organocerium complexes featuring Ce(IV)–C alkyl σ-bonds: [Ce(O)(CH3)(CH3CO2)2]– and [Ce(O)(CH3)(NO3)2]–. Attempts to isolate PrIV–CH3 and TbIV–CH3 were unsuccessful, however, fragmentation patterns reveal the oxidation of Ln(III) to a Ln(IV)-oxo-acetate complex is more favorable for praseodymium than terbium. The rate of Ln–CH3 hydrolysis is a measure of bond stability, and it decreases from La(III)–CH3 to Lu(III)–CH3, with increasing steric crowding for smaller Ln stabilizing the harder Ln–CH3 bond against hydrolysis. [Eu(CH3)(CH3CO2)2]– engages in much faster hydrolysis versus Ln(III)–CH3. The surprising observation of similar hydrolysis rates for Ce(IV)–CH3 and Ce(III)–CH3 is discussed with respect to sterics, the oxo ligand, and bond covalency in σ-bonded organolanthanides.