1,720,999 research outputs found
Donation and back-donation in cis- and trans-[(η5-C5H5)Fe(η1-CO)(μ-CO)]2 tautomers: Which relative is more generous? An ETS-NOCV bond analysis
No full textThe ETS-NOCV bond analysis has been exploited to quantitatively estimate donation and back-donation properties of [(η5-C5H5)]−, CO, and FeI in the cis-/trans-[(η5-C5H5)Fe(η1-CO)(μ-CO)]2 (cis-I/trans-I) tautomers. Theoretical outcomes indicate that the Fe-CO bond, regardless to the CO monoapto (η1-) or bridging (μ-) coordination, has a sizeable π Fe → CO back-bonding contribution, which is stronger in trans-I than in cis-I. Moreover, [(η5-C5H5)]− has the weakest back-donation acceptor capability. The back-bonding behaviour of the Fe → η1-CO interaction well agrees with the experimental symmetric/antisymmetric infrared νCO (sνηjavax.xml.bind.JAXBElement@fc12185-CO/aνηjavax.xml.bind.JAXBElement@4c260f05-CO) trend for cis-I and trans-I and further confirms the infrared classical behaviour of the η1-CO group in this class of complexes
Tra il mondo delle carte e il mondo delle cose. La chimica di Primo Levi, fra scienza della natura e e scienza dello spirito
No full textA theoretical study of the occupied and unoccupied electronic structure of high-and intermediate-spin transition metal phthalocyaninato (Pc) complexes: VPc, CrPc, MnPc, and FePc
Full text linkThe structural, electronic, and spectroscopic properties of high-and intermediate-spin transition metal phthalocyaninato complexes (MPc; M = V, Cr, Mn and Fe) have been theoretically investigated to look into the origin, symmetry and strength of the M–Pc bonding. DFT calculations coupled to the Ziegler’s extended transition state method and to an advanced charge density and bond order analysis allowed us to assess that the M–Pc bonding is dominated by σ interactions, with FePc having the strongest and most covalent M–Pc bond. According to experimental evidence, the lightest MPcs (VPc and CrPc) have a high-spin ground state (GS), while the MnPc and FePc GS spin is intermediate. Insights into the MPc unoccupied electronic structure have been gained by modelling M L2,3-edges X-ray absorption spectroscopy data from the literature through the exploitation of the current Density Functional Theory variant of the Restricted Open-Shell Configuration Interaction Singles (DFT/ROCIS) method. Besides the overall agreement between theory and experiment, the DFT/ROCIS results indicate that spectral features lying at the lowest excitation energies (EEs) are systematically generated by electronic states having the same GS spin multiplicity and involving M-based single electronic excitations; just as systematically, the L3-edge higher EE region of all the MPcs herein considered includes electronic states generated by metal-to-ligand-charge-transfer transitions involving the lowest-lying π* orbital (7eg) of the phthalocyaninato ligand
Growth and the structure of epitaxial VO2 at the TiO2(110) surface
No full textEpitaxial VO2 layers have been grown on the TiO2(110) rutile surface up to thicknesses of 5 ML. These ultrathin films have been characterized by means of x-ray photoelectron spectroscopy (XPS), x-ray photoelectron diffraction (XPD), low-energy electron diffraction (LEED), and ultraviolet photoelectron spectroscopy (UPS) measurements. LEED and XPD structural data demonstrate that the layer is both short- and long-range ordered, and that it has a rutile structure. The success in preparation of a single-crystalline epitaxial VO2 layer opens possibilities for studying the properties and the surface chemistry of this interesting oxide, so far complicated by the difficulties in growing macroscopic crystals. From the He I spectra it turns out that the shape, position, and width of the 3d band closely resemble the UPS data of the bulk monoclinic semiconductive phase. The reported results could add new clues to a better understanding of the metal-to-semiconductor phase-transition phenomenon in VO2
Early stages of epitaxial growth of vanadium oxide at the TiO2(110) surface studied by photoelectron diffraction
No full textThis paper reports experimental evidence for an incipient epitaxial growth of vanadium oxide at the TiO2(110) surface. This finding is based on a x-ray photoelectron diffraction and low-energy electron diffraction study of a submonolayer of vanadium deposited at the TiO2(110) surface, performed after annealing at 473 Ii in ultrahigh vacuum conditions. The data unambiguously show that vanadium atoms occupy selected sixfold-coordinated titanium sites which underbridge oxygen atoms of the topmost layer and that the TiO2(110) long-range surface structural order is preserved
On-surface Photochemistry of Pre-ordered 1-Methyl-2-phenyl-acetylenes: C-H Bond Activation and Intermolecular Coupling on Highly Oriented Pyrolytic Graphite
Full text linkIn thiscontributionwereporton light-inducedmetal-freecouplingof propynylbenzenemolecularunitsonhighlyorientedpyrolyticgraphite.The reactionoccurswithinthe self-assembledmonolayerandleadsto the generationof covalentlycoupled1,5-hexadiyneandpara terphenylderivativesundertopologicalcontrol. Such photochemical uncatalysed pathway represents an original approachin the fieldof topological C-C coupling at the solid/liquid interface and provides new insight into the low temperature formation of aromatic compounds at the surface of carbonaceous supports
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
cis-[(η5-C5H5)Fe(η1-CO)(μ-CO)]2, the poor relative betweencisandtranstautomers. A theoretical study of the gas-phase Fe L3-edge and C and O K-edge XAS oftrans-/cis-[(η5-C5H5)Fe(η1-CO)(μ-CO)]2
No full textThe relative stability oftrans-[(η5-C5H5)Fe(η1-CO)(μ-CO)]2(trans-I) andcis-Itautomers in a vacuum and in solvents with different dielectric constants (ε) has been investigated by exploiting density functional theory (DFT). Theoretical results indicate that, in agreement with experimental evidence,trans-Iis more stable thancis-Iin a vacuum (∼1.5 kcal mol−1;ε= 1), while the opposite is true in media withε> 7. Differently from solution, DFT outcomes pertaining to the vapor-phasecis-I⇆trans-Iequilibrium at T = 368 K, the temperature at which the Fe L2,3-edges and the C and O K-edge X-ray absorption spectroscopy (XAS) data ofIhave been recorded, ultimately indicate thetrans-Ipredominance (∼93%). Compositions, oscillator strengths (f) and excitation energy (EE) values ofcis-Itransitions substantially mirror those oftrans-I; nevertheless, the weightedcis-If(EE) distributions negligibly contribute to the diverse simulated XA spectra ofI
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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