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Synthesis, Structure, and Physicochemical Properties of ((Ethylsulfanyl)porphyrazinato)cobalt(II). Metal-Ligand Bonds in Co(OESPz) and in Related Cobalt(II) Tetrapyrroles: Insigths from a Density Functional Study
No full textThe Co(OESPz) complex crystallizes in space group P21/n, with a = 10.260(5) Å, b = 22.650(5) Å, c = 16.720(5) Å, β = 91.680(5)°, and Z = 4 and forms, similarly to the isomorphous Mn(OESPz), solid-state extended one-dimensional aggregates where “ruffled” molecular units are held together by extra planar Co···S interactions. The complex, which contains a low-spin Co2+ (S = 1/2) ion, exhibits intermolecular ferromagnetic interactions (θ = 2.6 K, g = 2.44) propagated through a superexchange pathway by extra planar Co···S interactions, with a possible contribution of the π system. Co(OESPz) shows a Co−Np distance shorter than CoOEP and CoPc and a sensible electrochemical stabilization of the Co2+ vs Co3+ state. The bonding interactions between Co2+ and the macrocyclic ligands OMSPz2-, Pc2-, Pz2-, and P2- are analyzed in detail, within the density functional (DF) theory, to elucidate the effects of the ligand framework. It is concluded that the σ interactions, which are by far dominant in all members of the CoII tetrapyrrole series, in the aza-bridged complexes, particularly in CoPz and Co(OMSPz), are stronger than in CoP, due to the reduced “hole” size of the macrocycle. The π interactions, consisting of π back-donation from Co-3dπ into empty ring π orbitals and donation from the occupied ring π orbitals into the Co-4pz are rather weak, but there is a sizable contribution from polarization of the macrocyclic ligand. The aza bridges have little effect on the metal to ligand π back-donation which in Co(OMSPz) is completely absent; the peripheral substituents, which are responsible for large polarization effects, play a more relevant role in the metal−macrocycle π interactions. In all porphyrazines the total orbital interaction contribution (covalent component) prevails over the ionic component of the bond, the latter being identified as the sum of the Pauli repulsion and the attractive electrostatic interaction between Co2+ and the tetrapyrrole(2−)
Complete structural and magnetic characterization of biological radicals in solution by an integrated quantum mechanical approach. Glycyl radical as a case study
No full textMapping the many electron generalised spin-exchange Hamiltonian to accurate post-HF calculations
No full textFIRST-PRINCIPLE MOLECULAR DYNAMICS OF THE BERRY PSEUDOROTATION: INSIGHT ON 19F NMR OF SF4
No full textFirst-principle molecular dynamics of the Berry pseudorotation: insights on 19F NMR in SF4
No full textFirst-principles density-functional theory DFT molecular-dynamic simulations of the Berry pseudorotation mechanism in SF4 were performed using the atom-centered density-matrix propagation method. The reaction was monitored by following the chemical shieldings of the fluorine atoms, computed on snapshots along the trajectories. In particular we compared the results obtained using a standard functional based on the generalized gradient approximation with those issuing from its hybrid Hartree–Fock–DFT counterpart using a number of basis sets. Our results show that both the basis set and the functional choice rule the quality of the molecular properties monitored as well as the trajectory over the potential-energy surface
Theoretical Insights on the Chemical Reactivity of MetalloPorphyrins Using Density Functional Theory
No full textGoing 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
Ab initio molecular dynamics based on density matrix propagation applied to the study of spectroscopic properties
No full textVariations 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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