1,721,109 research outputs found
A Cyclic Hexairon(III) Complex with an Octahedrally Coordinated Sodium Ion at the Center, an Example of the [12]Metallacrown–6 Structure Type
No full text[NaFe6(OMe)12(dbm)6]Cl·12MeOH·CHCl3 (I; dbmH = dibenzoylmethane) was prepd. and characterized by elemental anal., spectral (UV, IR), x-ray crystallog., and magnetic methods. The 6 Fe atoms are located at the vertexes of an almost regular hexagon, with Fe···Fe sepns. in the range 3.18-3.20 Å and vertex angles of 119.5-120.5°. The ring serves as a host for the Na ion. Antiferromagnetic exchange coupling interactions exist between the paramagnetic Fe(III) centers (J = 20 cm-1). I is a good structural model for cyclic intermediates proposed for the polyalc.-promoted hydrolysis of Fe(III) salts
Valence Tautomerism in a Cobalt Complex of a Schiff Base Diquinone Ligand
No full textThe cobalt(III) complex of a Schiff base diquinone ligand Co-III(Cat-N-BQ)(Cat-N-SQ) undergoes an entropy-driven valence tautomeric equilibrium in solution yielding the Co-II(Cat-N-BQ)(2) species. This suggestion is supported by variable temperature electronic and H-1 NMR spectra, as well as by solution magnetic susceptibility data. The calculated thermodynamic quantities associated to the redox equilibrium are Delta H = 42.0(0.8) kJ mol(-1) and Delta S = 140 (3) J mol(-1) K-1
Magnetism of Large Iron-Oxo Clusters
No full textThe role of large iron-ore clusters in chemistry, material science, and fundamental physics is briefly reviewed. Examples of clusters with nuclearity ranging from 6 to 19 are reported as well as their magnetic properties. Relevant topics, such as the role of spin topology and spin frustration in antiferromagnetically coupled systems and the observation of superparamagnetic like behaviour and molecular hysteresis, are discussed. The use of strong magnetic fields in the characterization of magnetic clusters is emphasized and a theoretical approach for the rationalization of the magnetic properties of clusters is briefly reported
NMR investigation of Gd(hfac)3NITEt fully frustrated helimagnet
No full textThe family of the quasi-1D molecular magnetic chains Gd(hfac)3NITR (where hfac is hexafluoro-acetylacetonate and NITR is 2-R-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-l-oxyl 3-oxyde) have assumed a great importance in the study of molecular magnets in the last 10 years. These chains develop along b crystallographic axis and consist in a regular pattern of Gd(hfac)3 moieties (S_Gd=7/2) alternated to nitronyl-nitroxide organic radicals NITR (R = iPr, Et, Ph, Me) (srad=1/2). In these derivatives the shortest interchain distance is about 10.5Å and, as a consequence, the ratio between interchain and intrachain exchange interactions is Jinter/Jintra1.9K while just below the transition temperature T(c)^3D=1.9K becomes suddenly much larger (>1 MHz), due to the insurgence of a local field Hloc at protons sites, generated by the ordered arrangement of the electronic spins
Nonadiabatic Landau Zener Tunneling and Quantum Phase Interference in Fe-8 Molecular Nanomagnets
No full textThe Landau-Zener method allows to measure very small tunnel splittings Δ in mol. clusters Fe8. The obsd. oscillations of Δ as a function of the magnetic field applied along the hard anisotropy axis are explained in terms of topol. quantum interference of two tunnel paths of opposite windings. Studies of the temp. dependence of the Landau-Zener transition rate P gives access to the topol. quantum interference between excited spin levels. The influence of nuclear spins is demonstrated by comparing P of the std. Fe8 sample with two isotopically substituted samples. The need of a generalized Landau-Zener transition rate theory is shown
Structure and Magnetic Properties of a Dodecanuclear Twisted-ring Iron(III) Cluster
No full text[Fe(OMe)2(dbm)]12 (I; Hdbm = dibenzoylmethane) was prepd. by the reaction of FeCl3 with Hdbm in presence of KOMe or CsOMe in anhyd. MeOH. I.6CHCl3 is monoclinic, space group P21/c, Z = 4, R = 0.0967, Rw = 0.3174. Each Fe(III) in I has a distorted octahedral environment with 6 O atoms from methoxide and dbm with Fe-O band lengths of 1.94-2.07 Å, forming a twisted ring which is not planar and has C1 point group symmetry. NMR data of I in presence of NaBPh4 or LiBPh4 indicate that I is quant. converted to hexairon(III) coronates, [MFe6(OMe)12(dbm)6]+. Magnetic susceptibility data indicate antiferromagnetic coupling in I between high-spin Fe(III) atoms
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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