Pere Miró

On the Origin of the Cation Templated Self-Assembly of Uranyl-Peroxide Nanoclusters

Uranyl-peroxide nanoclusters display different topologies based on square, pentagonal and hexagonal building blocks. Computed complexation energies of different cations (Li(+), Na(+), K(+), Rb(+), and Cs(+)) with [UO(2)(O(2))(H(2)O)](n) (n = 4, 5, and 6) macrocycles suggest a strong cation templating effect. The inherent bent structure of a U-O(2)-U model dimer is demonstrated and justified through the analysis of its electronic structure, as well as of the inherent curvature of the four-, five-, and six-uranyl macrocyles. The curvature is enhaced by cation coordination, which is suggested to be the driving force for the self-assembly of the nanocapsules.

Two Dimensional Materials Beyond MoS2: Noble‐Transition‐Metal Dichalcogenides

The structure and electronic structure of layered noble-transition-metal dichalcogenides MX2 (M=Pt and Pd, and chalcogenides X=S, Se, and Te) have been investigated by periodic density functional theory (DFT) calculations. The MS2 monolayers are indirect band-gap semiconductors whereas the MSe2 and MTe2 analogues show significantly smaller band gap and can even become semimetallic or metallic materials. Under mechanical strain these MX2 materials become quasi-direct band-gap semiconductors. The mechanical-deformation and electron-transport properties of these materials indicate their potential application in flexible nanoelectronics.

On the nature of actinide- and lanthanide-metal bonds in heterobimetallic compounds.

Eleven experimentally characterized complexes containing heterobimetallic bonds between elements of the f-block and other elements were examined by quantum chemical methods: [(η(5)-C(5)H(5))(2)(THF)LuRu(η(5)-C(5)H(5))(CO)(2)], [(η(5)-C(5)Me(5))(2)(I)ThRu(η(5)-C(5)H(5))(CO)(2)], [(η(5)-C(5)H(5))(2)YRe(η(5)-C(5)H(5))(2)], [{N(CH(2)CH(2)NSiMe(3))(3)}URe(η(5)-C(5)H(5))(2)], [Y{Ga(NArCh)(2)}{C(PPh(2)NSiH(3))(2)}(CH(3)OCH(3))(2)], [{N(CH(2)CH(2)NSiMe(3))(3)}U{Ga(NArCH)(2)}(THF)], [(η(5)-C(5)H(5))(3)UGa(η(5)-C(5)Me(5))], [Yb(η(5)-C(5)H(5)){Si(SiMe(3))(3)(THF)(2)}], [(η(5)-C(5)H(5))(3)U(SnPh(3))], [(η(5)-C(5)H(5))(3)U(SiPh(3))], and (Ph[Me]N)(3)USi(SiMe(3))(3). Geometries in good agreement with experiment were obtained at the density functional level of theory. The multiconfigurational complete active space self-consistent field method (CASSCF) and subsequent corrections with second order perturbation theory (CASPT2) were applied to further understand the electronic structure of the lanthanide/actinide-metal (or metal-metalloid) bonds. Fragment calculations and energy-decomposition analyses were also performed and indicate that charge transfer occurs from one supported metal fragment to the other, while the bonding itself is always dominated by ionic character.

Spontaneous Ripple Formation in MoS2 Monolayers: Electronic Structure and Transport Effects

The spontaneous formation of ripples in molybdenum disulfide (MoS2 ) monolayers is investigated via density functional theory based tight-binding Born-Oppenheimer molecular dynamics. Monolayers with different lengths show spontaneous rippling during the simulations. The density of states reveals a decrease in the bandgap induced by the stretching of the MoS2 units due to ripple formation. Significant quenching in electron conductance was also observed. The ripples in the MoS2 monolayers have an effect on the properties of the material and could impact its application in nanoelectronics.

Colloidal synthesis of single-layer MSe2 (M = Mo, W) nanosheets via anisotropic solution-phase growth approach.

The generation of single-layer 2-dimensional (2D) nanosheets has been challenging, especially in solution-phase, since it requires highly anisotropic growth processes that exclusively promote planar directionality during nanocrystal formation. In this study, we discovered that such selective growth pathways can be achieved by modulating the binding affinities of coordinating capping ligands to the edge facets of 2D layered transition-metal chalcogenides (TMCs). Upon changing the functional groups of the capping ligands from carboxylic acid to alcohol and amine with accordingly modulated binding affinities to the edges, the number of layers of nanosheets is controlled. Single-layer MSe2 (M = Mo, W) TMC nanosheets are obtained with the use of oleic acid, while multilayer nanosheets are formed with relatively strong binding ligands such as oleyl alcohol and oleylamine. With the choice of appropriate capping ligands in the 2D anisotropic growth regime, our solution-based synthetic method can serve a new guideline for obtaining single-layer TMC nanosheets.

Electronic structure of oxidized complexes derived from cis-[Ru II(bpy) 2(H 2O) 2] 2+ and its photoisomerization mechanism

The geometry and electronic structure of cis-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) and its higher oxidation state species up formally to Ru(VI) have been studied by means of UV-vis, EPR, XAS, and DFT and CASSCF/CASPT2 calculations. DFT calculations of the molecular structures of these species show that, as the oxidation state increases, the Ru-O bond distance decreases, indicating increased degrees of Ru-O multiple bonding. In addition, the O-Ru-O valence bond angle increases as the oxidation state increases. EPR spectroscopy and quantum chemical calculations indicate that low-spin configurations are favored for all oxidation states. Thus, cis-[Ru(IV)(bpy)(2)(OH)(2)](2+) (d(4)) has a singlet ground state and is EPR-silent at low temperatures, while cis-[Ru(V)(bpy)(2)(O)(OH)](2+) (d(3)) has a doublet ground state. XAS spectroscopy of higher oxidation state species and DFT calculations further illuminate the electronic structures of these complexes, particularly with respect to the covalent character of the O-Ru-O fragment. In addition, the photochemical isomerization of cis-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) to its trans-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) isomer has been fully characterized through quantum chemical calculations. The excited-state process is predicted to involve decoordination of one aqua ligand, which leads to a coordinatively unsaturated complex that undergoes structural rearrangement followed by recoordination of water to yield the trans isomer.

A Journey inside the U28 Nanocapsule

Anionic uranyl-peroxide U(28) nanocapsules trap cations and other anions inside, whose structures cannot be resolved by X-ray diffraction, owing to crystallographic disorder. DFT calculations enabled the complete characterization of the geometry of these complex systems and also explained the origin of the disorder. The stability of the capsules was strongly influenced by the entrapped cations. Excellent agreement between experiment and theory was also obtained for the electronic character and redox properties.

Experimental and Computational Study of a New Wheel-Shaped {[W5O21]3[(UVIO2)2(μ-O2)]3}30– Polyoxometalate

A new wheel-shaped polyoxometalate {[W(5)O(21)](3)[(U(VI)O(2))(2)(μ-O(2))](3)}(30-) has been synthesized and structurally characterized. The calculated electrostatic potential reveals the protonation of several μ-oxo bridges reducing the polyoxometalate total charge. A protonated structure computed at the density functional level of theory (DFT) is in good agreement with the experimental fit. This species presents a classical polyoxometalate electronic structure with well-defined metal and oxo bands belonging to its U/W and oxo/peroxo constituents, respectively. Furthermore, fragment calculations indicate that the electronic structures of the uranyl-peroxide and polyoxotugstate fragments are little affected by the nanowheel assembly.

Uranyl-peroxide nanocapsules: electronic structure and cation complexation in [(UO2)20(μ-O2)30]20-.

The pentagonal K(10)[(UO(2))(5)(μ-O(2))(5)(C(2)O(4))(5)] species have been identified as the building blocks of uranyl-peroxide nanocapsules. The computed complexation energies of different alkali cations (Li(+), Na(+), K(+), Rb(+), and Cs(+)) with [(UO(2))(5)(μ-O(2))(5)(O(2))(5)](10-) and [(UO(2))(20)(μ-O(2))(30)](20-) species suggest a strong cation templating effect. In the studied species, the largest complexation energy occurs for the experimentally used alkali cations (Na(+) and K(+)).

Dynamics of Encapsulated Water inside Mo132 Cavities

The structure and dynamics of water confined inside a polyoxomolybdate molecular cluster [{(Mo)Mo(5)O(21)(H(2)O)(6)}(12){Mo(2)O(4)(SO(4))}(30)](72-) metal oxide nanocapsule have been studied by means of molecular dynamics simulations under ambient conditions. Our results are compared to experimental data and theoretical analyses done in reverse micelles, for several properties. We observe that the characteristic three-dimensional hydrogen bond network present in bulk water is distorted inside the cavity where water organizes instead in concentric layered structures. Hydrogen bonding, tetrahedral order, and orientational distribution analyses indicate that these layers are formed by water molecules hydrogen bonded with three other molecules of the same structure. The remaining hydrogen bond donor/acceptor site bridges different layers as well as the whole structure with the hydrophilic inner side of the cavity. The most stable configuration of the layers is thus that of a buckyball with 12 pentagons and a variable number of hexagons. The geometrical constraints make it so that the bridges between the layers display a significant degree of frustration. The main modes of motion at short times are correlated fluctuations of the entire system with a characteristic frequency. Switches of water molecules between layers are rare events, due to the stability of the layers. At long times, the system shows a power law decay (pink noise) in properties like the fluctuations in the number of molecules in the structures and the total dipole moment. Such behavior has been attributed to the complex relaxation of the hydrogen bond network, and the exponents found are close to those encountered in bulk water for the relaxation of the potential energy. Our results reveal the importance of the competition between the confinement and the long-range structure induced in this system by the hydrogen bond network.