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.

A density functional study of the adsorption of methane-thiol on the (111) surfaces of the Ni-group metals: I. Molecular and dissociative adsorption.

The molecular and dissociative adsorption of methane-thiol (CH(3)SH) in the high-coverage limit on the (111) surfaces of the Ni-group metals has been investigated using ab initio density functional techniques. In molecular form, methane-thiol is bound to the surface only by weak polarization-induced forces in a slightly asymmetric configuration with the C-S axis tilted by 35-60° relative to the surface normal. On Ni and Pd surfaces the S atom occupies a position close to a bridge site; on Pt it is located close to an on-top position. The length of the S-H bond is only slightly stretched relative to its value in the gas phase, indicating only a very modest degree of activation for dehydrogenation. A strong covalent adsorbate/substrate bond is formed upon adsorption of a methane-thiolate (CH(3)S) radical. On Ni(111) in the energetically most favorable configuration the S atom occupies a position in a threefold hollow, slightly displaced towards a bridge site. The C-S axis is tilted by about 35° across the bridge. On Pd(111) and Pt(111) the S atom of thiolate occupies a position between a hollow and a bridge site, with the C-S axis tilted even more strongly across a neighboring threefold hollow. On all three surfaces our calculations demonstrate the existence of multiple metastable adsorption configurations, including upright CH(3)S bound in the center of a threefold hollow as reported in some earlier studies. Dehydrogenation of the adsorbed methane-thiol to form co-adsorbed methane-thiolate and atomic hydrogen is an exothermic process, which is not activated on Ni(111) but activated on Pd(111) and Pt(111).

A density-functional study of the adsorption of methane-thiol on the (111) surfaces of the Ni-group metals: II. Vibrational spectroscopy.

The vibrational eigenstates of methane-thiol (CH(3)SH) and methane-thiolate (CH(3)S) in the gas phase and in dense monolayers adsorbed on the (111) surfaces of the Ni-group metals have been investigated within the framework of density-functional theory using generalized response and force-constant techniques. For isolated CH(3)SH good agreement of eigenfrequencies and intensities with the measured infrared spectra is achieved. For the CH(3)S radical, experimental information from laser-induced fluorescence spectroscopy is available only for selected eigenmodes. The theoretical predictions show reasonable agreement for the C-H deformation and C-S stretching modes, but predict much higher C-H stretching frequencies in better agreement with estimates based on the vibrational fine structure of the photoemission spectra. For methane-thiol monolayers on Ni(111) and Pt(111) the calculations predict stronger red-shifts of the S-H and C-S stretching modes than reported from high-resolution electron energy loss spectroscopy (HREELS) on condensed multilayers which average over the first layer adsorbed on the metal and further physisorbed molecular layers. For methane-thiolate monolayers the calculations predict modest blue-shifts of the C-H stretching and rocking modes and for the asymmetric C-H deformation modes. Red-shifts are predicted for the symmetric C-H deformation and for the C-S stretching modes. Reasonable agreement with HREELS is achieved. The increased differences between symmetric and asymmetric C-H stretching and deformation modes induced by the adsorption is a consequence of the strongly tilted adsorption geometries.

The platinum-olefin binding energy in series of (PH3)2Pt(olefin) complexes--a theoretical study.

Theoretical investigation of Pt(0)-olefin organometallic complexes containing tertiary phosphine ligands was focused on the strength of platinum-olefin electronic interaction. DFT theoretical study of electronic effects in a substantial number of ethylene derivatives was evaluated in terms of the Pt-olefin binding energy using MP2 correlation theory. Organometallics bearing coordinated olefins with general formula (R1R2C = CR3R4)Pt(PH3)2 [R = various substituents] had been selected, including olefins containing both electron-donor substituents as well as electron-withdrawing groups. The stability of the corresponding complexes increases with a strengthening electron-withdrawal ability of the olefin substituents.