Chemistry of iridium carbonyl cluster complexes. Synthesis,characterization and solid state structure of the phosphido carbonyl cluster [Ir6(CO)12(μ-CO)2(μ-PPh2)−

The phosphido-bridged cluster [Ir₆(CO)₁₄ PPh2]^– has been obtained by reaction of [Ir₆(CO)₁₅]^2– with PHPh₂, in the presence of ferrocenium cation, followed by deprotonation. The anion was isolated as a salt of [N(PPh₃)₂]⁺ or K⁺ and its structure was determined by single crystal X-ray data analysis. The salt [N(PPh₃)₂][Ir₆(CO)₁₄PPh₂] crystallizes in the triclinic space group P witha = 11.835(1) Å,b = 15.007(1) Å,c = 18.766(2)_ Å; = 78.779(7)°, = 87.260(8)°, = 75.794(6)°,V = 3169.3(7) Å,Z = 2. The structure was solved by Direct Methods and Difference Fourier techniques and refined down toR andR _w values of 0.034 and 0.036, respectively, for 8003 observed reflections havingl > 3(I). The octahedral anion, of idealized C₂ symmetry, possesses two distance Ir-P = 2.284 Å, formally acting as a three electron donor. Average bond distances (Å) and angles (degrees) are: Ir-Ir = 2.776, Ir-C _t = 1.87, Ir-C _b = 2.05, C _t -O _t = 1.14, C _b -O_b= 1.17, Ir-P-Ir = 74.3°, Ir-C _t -O _t = 177°, Ir-C _b -O _b = 138°, Ir-C _b -Ir = 84° (t = terminal,b = bridging).     

On the Degeneracy Locus of a Map of Vector Bundles on Grassamannian Varieties

Let ℒ︁ be a line bundle on a smooth curve C of genus g ≥ 2 and let W ⊂ H⁰ (ℒ︁) be a subspace of dimension r +1, in this paper we study the natural map μ_W : W ⊗ H⁰ (ω_C) → H⁰ (ℒ︁ ⊗ ω_C). Let D ⊂ G(r + 1, H⁰(ℒ︁)) be the locus where μ_W fails to be surjective: we prove that, if C is not hyperelliptic of genus g ≥ 3, D is an irreducible and reduced divisor on G(r + 1, H⁰(ℒ︁)) for any r ≥ 3, and for r = 2 if the curve C is not trigonal.     

Effect of Au proximity on the LSMO surface: An ab initio study

The effect of the proximity of Au on the electronic and magnetic properties of La_0.66Sr_0.33MnO₃ (LSMO) has been investigated by means of ab initio calculations within the density-functional theory. The calculations show an orbital reconstruction of the interfacial Mn, which is due more to the presence of a discontinuity rather than to a real chemical interaction with Au atoms. In fact, the same orbital reconstruction is found in the free LSMO surface. In both cases of Au/LSMO and LSMO surface, the Mn magnetic moments change very little with respect to the bulk case. In general, the calculations show a negligible influence of the Au atomic layer on LSMO at an ideal interface, with the LSMO surface magnetic and electronic properties essentially unchanged.     

Effect of viscous dissipation on the mixed convection heat transfer from an exponentially stretching surface

The mixed convection flow and heat transfer from an exponentially stretching vertical surface in a quiescent fluid is analyzed using similarity solution technique. Wall temperature and stretching velocity are assumed to have specific exponential function forms. The influence of buoyancy along with viscous dissipation on the convective transport in the boundary layer region is analyzed in both aiding and opposing flow situations. The flow is governed by the mixed convection parameter Gr/Re². The velocity and temperature inside the boundary layer are observed to be influenced by the parameters like Prandtl number Pr, Gebhart number Gb. Significant changes are observed in non-dimensional skin friction and heat transfer coefficients due to viscous dissipation in the medium. The flow and temperature distributions inside the boundary layer are analyzed and the results for non-dimensional skin friction and heat transfer coefficients are discussed through computer generated plots.     

Adsorption of H<Subscript>2</Subscript>S,HS, S,and H on a stepped Fe(310) surface

Using periodic density functional theory we studied adsorption of H₂S, HS, S and H on the Fe(310) stepped surface, comparing our results with those on Fe(100). H₂S is predicted to weakly adsorb on all high-symmetry sites, with the bridge site at the step edge as preferred one, oriented perpendicularly to the (100) terraces with the two H atoms pointing out of the surface. Adsorption of HS, S, and H is more stable on the bridge, four-fold hollow, and three-fold hollow sites, respectively. The detailed analysis of the computed local density of states show common trends with the behavior of adsorption energies and is able to account for energy differences of all species adsorbed on Fe(100) and Fe(310).     

Corrugating and anticorrugating static interactions in helium-atom scattering from metal surfaces

We perform a density-functional-theory calculation of the static repulsive potential of He scattering off a noble and a simple metal surface. The classical turning point of He on Cu(111) is found to be closer to the metal when the adatom is at top than at bridge site (anticorrugating effect). The potential of He on Al(111) is instead corrugated. By comparing the results of the two systems, we conclude that the He-metal anticorrugating effect occurs when the kinetic energy difference for He at top and bridge sites is larger than the electrostatic one, and an induced localized dipole on He is formed.     

Simple chip-based interfaces for on-line monitoring of supramolecular interactions by nano-ESI MS

Two simple interfaces were designed and realized, enabling on-line coupling of microfluidics reactor chips to a nanoflow electrospray ionization (NESI) time-of-flight (TOF) mass spectrometer (MS). The interfaces are based on two different approaches: a monolithically integrated design, in which ionization is assisted by on-chip gas nebulization, and a modular approach implying the use of commercially available Picospray tips. Using reserpine as a reference compound in a 1ratio1 mixture of acetonitrile and water revealed that both interfaces provide a remarkably stable mass spectrometric signal (standard deviations lower than 8% and 1% for the monolithic and modular approaches, respectively). Glass microreactors, containing mixing zones, were fabricated and coupled to the modular interface with perfluoroelastomer Nanoport fluidics connectors, providing a tool to study chemical reactions on-line. Investigation of the mixing dynamics showed that complete on-chip reagents mixing is achieved within a few tens of milliseconds. Metal-ligand interactions of Zn-porphyrin with pyridine (2), 4-ethylpyridine (3), 4-phenylpyridine (4), N-methylimidazole (5), and N-butylimidazole (6) in acetonitrile as well as host-guest complexations of beta-cyclodextrin (7) with N-(1-adamantyl)acetamide (8) or 4-tert-butylacetanilide (9) in water were studied by mass spectrometry using the modular NESI-chip interface. From on-chip dilution-based mass spectrometric titrations of Zn-porphyrin 1 with pyridine (2) or 4-phenylpyridine (4) in acetonitrile Ka-values of 4.6 +/- 0.4 x 10(3) M(-1) and 6.5 +/- 1.2 x 10(3) M(-1), respectively, were calculated. The Ka-values are about four times larger than those obtained with UV/vis spectroscopy in solution, probably due to a higher ionization efficiency of complexed compared to uncomplexed Zn-porphyrin. For the complexation of N-(1-adamantyl)acetamide (8) with beta-cyclodextrin (7), a Ka-value of 3.6 +/- 0.3 x 10(4) M(-1) was obtained, which is in good agreement with that determined by microcalorimetry.     

Absorption and resonant Raman scattering from trans-(CH)x

Fully conistent calculations of absorption and RRS scattering spectra have been performed by using a bimodal gaussian distribution centered on long and short chains, which constitute trans-polyacetylene samples. They in good agreement with the experimental data and allow pedictions on the conjugation length of trans-polyacetylene chains.