Daniel Rios

Gas-Phase Uranyl, Neptunyl, and Plutonyl: Hydration and Oxidation Studied by Experiment and Theory

The following monopositive actinyl ions were produced by electrospray ionization of aqueous solutions of An(VI)O(2)(ClO(4))(2) (An = U, Np, Pu): U(V)O(2)(+), Np(V)O(2)(+), Pu(V)O(2)(+), U(VI)O(2)(OH)(+), and Pu(VI)O(2)(OH)(+); abundances of the actinyl ions reflect the relative stabilities of the An(VI) and An(V) oxidation states. Gas-phase reactions with water in an ion trap revealed that water addition terminates at AnO(2)(+)·(H(2)O)(4) (An = U, Np, Pu) and AnO(2)(OH)(+)·(H(2)O)(3) (An = U, Pu), each with four equatorial ligands. These terminal hydrates evidently correspond to the maximum inner-sphere water coordination in the gas phase, as substantiated by density functional theory (DFT) computations of the hydrate structures and energetics. Measured hydration rates for the AnO(2)(OH)(+) were substantially faster than for the AnO(2)(+), reflecting additional vibrational degrees of freedom in the hydroxide ions for stabilization of hot adducts. Dioxygen addition resulted in UO(2)(+)(O(2))(H(2)O)(n) (n = 2, 3), whereas O(2) addition was not observed for NpO(2)(+) or PuO(2)(+) hydrates. DFT suggests that two-electron three-centered bonds form between UO(2)(+) and O(2), but not between NpO(2)(+) and O(2). As formation of the UO(2)(+)-O(2) bonds formally corresponds to the oxidation of U(V) to U(VI), the absence of this bonding with NpO(2)(+) can be considered a manifestation of the lower relative stability of Np(VI).

Electron transfer dissociation of dipositive uranyl and plutonyl coordination complexes.

Reported here is a comparison of electron transfer dissociation (ETD) and collision-induced dissociation (CID) of solvent-coordinated dipositive uranyl and plutonyl ions generated by electrospray ionization. Fundamental differences between the ETD and CID processes are apparent, as are differences between the intrinsic chemistries of uranyl and plutonyl. Reduction of both charge and oxidation state, which is inherent in ETD activation of [An(VI) O(2) (CH(3) COCH(3) )(4) ](2+) , [An(VI) O(2) (CH(3) CN)(4) ](2) , [U(VI) O(2) (CH(3) COCH(3) )(5) ](2+) and [U(VI) O(2) (CH(3) CN)(5) ](2+) (An = U or Pu), is accompanied by ligand loss. Resulting low-coordinate uranyl(V) complexes add O(2) , whereas plutonyl(V) complexes do not. In contrast, CID of the same complexes generates predominantly doubly-charged products through loss of coordinating ligands. Singly-charged CID products of [U(VI) O(2) (CH(3) COCH(3) )(4,5) ](2+) , [U(VI) O(2) (CH(3) CN)(4,5) ](2+) and [Pu(VI) O(2) (CH(3) CN)(4) ](2+) retain the hexavalent metal oxidation state with the addition of hydroxide or acetone enolate anion ligands. However, CID of [Pu(VI) O(2) (CH(3) COCH(3) )(4) ](2+) generates monopositive plutonyl(V) complexes, reflecting relatively more facile reduction of Pu(VI) to Pu(V).

Gas-Phase Coordination Complexes of Dipositive Plutonyl, PuO22+: Chemical Diversity Across the Actinyl Series

We report the first transmission of solvent-coordinated dipositive plutonyl ion, Pu(VI)O(2)(2+), from solution to the gas phase by electrospray ionization (ESI) of plutonyl solutions in water/acetone and water/acetonitrile. ESI of plutonyl and uranyl solutions produced the isolable gas-phase complexes, [An(VI)O(2)(CH(3)COCH(3))(4,5,6)](2+), [An(VI)O(2)(CH(3)COCH(3))(3)(H(2)O)](2+), and [An(VI)O(2)(CH(3)CN)(4)](2+); additional complex compositions were observed for uranyl. In accord with relative actinyl stabilities, U(VI)O(2)(2+) > Pu(VI)O(2)(2+) > Np(VI)O(2)(2+), the yields of plutonyl complexes were about an order of magnitude less than those of uranyl, and dipositive neptunyl complexes were not observed. Collision-induced dissociation (CID) of the dipositive coordination complexes in a quadrupole ion trap produced doubly- and singly-charged fragment ions; the fragmentation products reveal differences in underlying chemistries of plutonyl and uranyl, including the lower stability of Pu(VI) as compared with U(VI). Particularly notable was the distinctive CID fragment ion, [Pu(IV)(OH)(3)](+) from [Pu(VI)O(2)(CH(3)COCH(3))(6)](2+), where the plutonyl structure has been disrupted and the tetravalent plutonium hydroxide produced; this process was not observed for uranyl.

Gas-phase coordination complexes of (UO22+)-O-VI, (NpO22+)-O-VI, and (PuO22+)-O-VI with dimethylformamide

Electrospray ionization of actinyl perchlorate solutions in H2O with 5% by volume of dimethylformamide (DMF) produced the isolatable gas-phase complexes, [AnVIO2(DMF)3(H2O)]2+ and [AnVIO2(DMF)4]2+, where An = U, Np, and Pu. Collision-induced dissociation confirmed the composition of the dipositive coordination complexes, and produced doubly- and singly-charged fragment ions. The fragmentation products reveal differences in underlying chemistries of uranyl, neptunyl, and plutonyl, including the lower stability of Np(VI) and Pu(VI) compared with U(VI).

Gas-Phase Coordination Complexes of UVIO22+, NpVIO22+, and PuVIO22+ with Dimethylformamide

Electrospray ionization of actinyl perchlorate solutions in H2O with 5% by volume of dimethylformamide (DMF) produced the isolatable gas-phase complexes, [AnVIO2(DMF)3(H2O)]2+ and [AnVIO2(DMF)4]2+, where An = U, Np, and Pu. Collision-induced dissociation confirmed the composition of the dipositive coordination complexes, and produced doubly- and singly-charged fragment ions. The fragmentation products reveal differences in underlying chemistries of uranyl, neptunyl, and plutonyl, including the lower stability of Np(VI) and Pu(VI) compared with U(VI).

Blue or Green Glowing Crystals of the Cation [Au{C(NHMe)2}2]+. Structural Effects of Anions, Hydrogen Bonding, and Solvate Molecules on the Luminescence of a Two-Coordinate Gold(I) Carbene Complex

Depending upon the crystallization conditions, [Au{C(NHMe) 2} 2](AsF 6) forms colorless crystals that display a blue or green luminescence. The difference involves the type of solvate molecule that is incorporated into the crystal and the structure of the chains of cations that are formed upon crystallization. The crystallographically determined structures of blue-glowing [Au{C(NHMe) 2} 2](AsF 6).0.5(benzene), blue-glowing [Au{C(NHMe) 2} 2](AsF 6).0.5(acetone), green-glowing [Au{C(NHMe) 2} 2](AsF 6).0.5(chlorobenzene), and blue-glowing, solvate-free [Au{C(NHMe) 2} 2](EF 6), E = P, As, Sb are reported. All pack with the cations forming extended columns, which may be linear or bent, but all show significant aurophilic interactions. The blue-glowing crystals have ordered stacks of cations with some variation in structural arrangement whereas the green-glowing crystals have disorder in their stacking pattern. Although there is extensive hydrogen bonding between the cations and anions in all structures, in the solvated crystals, the solvate molecules occupy channels but make no hydrogen-bonded contacts. The emission spectra of these new salts taken at 298 and 77 K are reported.

New Tetraazaannulene Hosts for Fullerenes

Two modifications to the doubly concaved host molecules based on well-known nickel tetraazaannulene complexes have resulted in the preparation of the compounds Ni(NapTMTAA).2benzene, 1,6,8,15,17-tetramethyldinapthalene-5,9,14,18-tetraazacyclotetradecinatonickel(II), and Ni(Cl(4)TMTAA).CH(2)Cl(2), 2,3,11,12-tetrachloro-6,8,15,17-tetramethyldibenzo-5,9,14,18-tetraazacyclotetradecinatonickel(II). When crystallized with C(60) in carbon disulfide, the crystalline, well-ordered, host-guest compounds Ni(NapTMTAA).C(60).2CS(2) and Ni(Cl(4)TMTAA).C(60).2CS(2) were formed. The compounds were characterized by X-ray crystallography. The crystal structures of the precursor host molecules showed very strong host-host interactions, particularly in the case of Ni(Cl(4)TMTAA), which had short Ni...Ni interactions of 3.3860(11) and 3.5888(11) A in the two different dimers in the asymmetric unit; yet, these host-host interactions were entirely destroyed in the resultant host-guest compounds, and C(60) molecules were shown to make use of both cusps of the host macrocycle in the formation of a shape-selective arrangement.

Blue-, green- and non-luminescent crystals from one reaction. Isolation and structural characterization of a series of gold(I)-silver(I) heterometallic complexes utilizing a gold carbene metalloligand containing free amino groups.

The metalloligand [Au{C(NHMe)(NHCH(2)CH(2)NH(2))}(2)]Cl, 1, has been prepared by the reaction of ethylenediamine with [Au(CNMe)(2)]Cl. Compound 1 crystallized as a luminescent dimer with a Au...Au separation of 3.0224(4) A. It reacted in solution with silver hexafluorophosphate to form the coordination polymer, {[Au{mu-C(NHMe)(NHCH(2)CH(2)NH(2))}(2)Ag(NCMe)](PF(6))(2)}(n), 2. The structure of 2 involves a chain of alternating gold(I) and silver(I) ions with a Au...Ag distance of 2.9694(4)A. The reaction of the metalloligand, 1, with silver tetrafluoroborate yielded three products: the green luminescent coordination polymer, {[Au{mu-C(NHMe)(NHCH(2)CH(2)NH(2))}(2)Ag-(NCMe)](BF(4))(2)}(n), 3, which is analogous to 2; the non-luminescent binuclear complex, [Au{mu-C(NHMe)(NHCH(2)CH(2)NH(2))}(2)Ag](BF(4))(2), 4; and the blue luminescent complex, [{mu-C(NHMe)NHCH(2)CH(2)NH(MeHN)C}Au(2){mu-C(NHMe)(NHCH(2)CH(2)NH(2))}(2)Ag](BF(4))(3-) x 3(MeCN), 5. Compound 5 involves a bent Au...Ag...Au cation with two different Au...Ag distances (2.9165(8) A and 3.1743(8) A). This cation self-associates through a Au...Au interaction of 3.0275(5) A, which allows the formation of an extended zigzag chain of cations in 5.

On the Formation of “Hypercoordinated” Uranyl Complexes

Recent gas-phase experimental studies suggest the presence of hypercoordinated uranyl complexes. Coordination of acetone (Ace) to uranyl to form hypercoordinated species is examined using density functional theory (DFT) with a range of functionals and second-order perturbation theory (MP2). Complexes with up to eight acetones were studied. It is shown that no more than six acetones can bind directly to uranium and that the observed uranyl complexes are not hypercoordinated. In addition, other more exotic species involving proton transfer between acetones and species involving enol tautomers of acetone are high-energy species that are unlikely to form.

Activation of Gas-Phase Uranyl: From an Oxo to a Nitrido Complex

The uranyl moiety, UO2(2+), is ubiquitous in the chemistry of uranium, the most prevalent actinide. Replacing the strong uranium-oxygen bonds in uranyl with other ligands is very challenging, having met with only limited success. We report here uranyl oxo bond activation in the gas phase to form a terminal nitrido complex, a previously elusive transformation. Collision induced dissociation of gas-phase UO2(NCO)Cl2(-) in an ion trap produced the nitrido oxo complex, NUOCl2(-), and CO2. NUOCl2(-) was computed by DFT to have Cs symmetry and a singlet ground state. The computed bond length and order indicate a triple U-N bond. Endothermic activation of UO2(NCO)Cl2(-) to produce NUOCl2(-) and neutral CO2 was computed to be thermodynamically more favorable than NCO ligand loss. Complete reaction pathways for the CO2 elimination process were computed at the DFT level.