Reinvestigation of Reactions of HgPh<inf>2</inf> with Eu and Yb Metal and the Synthesis of a Europium(II) Bis(tetraphenylborate) †

Europium bis(tetraphenylborate) [Eu(thf)7][BPh4]2⋅thf containing a fully solvated [Eu(thf)7]2+ cation, was synthesized by protolysis of “EuPh2” (from Eu and HgPh2) with Et3NHBPh4, and the structure was determined by single-crystal X-ray diffraction. Efforts to characterize the putative “Ph2Ln” (Ln = Eu, Yb) reagents led to the synthesis of a mixed-valence complex, [(thf)3YbII(μ-Ph)3YbIII(Ph)2(thf)]⋅2thf, resulting from the reaction of Yb metal with HgPh2 at a low temperature. This mixed-valence YbII/YbIII compound was studied by 171Yb-NMR spectroscopy and single-crystal X-ray diffraction, and the oxidation states of the Yb atoms were assigned

An unprecedented phosphinine with significant P(π)-donor properties

A hitherto unprecedented electronic situation has been observed for a substituted, pyridyl-functionalized phosphinine. In contrast to previous studies, this compound shows considerable π-donor properties as the result of the rather strong +M effect of the CH3S-substituent, changing the electronic properties of this low-coordinate and aromatic phosphorus heterocycle substantially

Self-Similarity and Localization

The localized eigenstates of the Harper equation exhibit universal self-similar fluctuations once the exponentially decaying part of a wave function is factorized out. For a fixed quantum state, we show that the whole localized phase is characterized by a single strong coupling fixed point of the renormalization equations. This fixed point also describes the generalized Harper model with next nearest neighbor interaction below a certain threshold. Above the threshold, the fluctuations in the generalized Harper model are described by a strange invariant set of the renormalization equations.Comment: 4 pages, RevTeX, 2 figures include

The localization transition in the Aubry model through maps

The equation of motion for the wave function of the 1-d Aubry model is analyzed through a 3-d map which couples the modulation parameter γ and the integrated density of states k. Numerical results are presented for constant γ and k for energy E = 0 as a function of the potential strength V. The localization transition is found at V = 2 as the disappearance of a well defined curve into a cloud of points. The curves grow in complexity when approaching the critical value from below. We define a mean radius for the xy-plane projection of the 3-d map and we show numerically that it converges to a finite constant for V < 2. Also, its critical behavior is analyzed for V equal to the golden mean. Comments are made on previous results concerning disordered chains.L'équation de mouvement pour le modèle d'Aubry unidimensionnel est étudiée à l'aide d'une application 3-d qui couple le paramètre de modulation γ avec la densité d'états intégrée k. Nous présentons des résultats numériques pour l'énergie E = 0 et pour γ et k constants en fonction du potentiel V. Pour V = 2 la transition de localisation se manifeste par le passage d'une courbe bien définie à un nuage de points. La complexité des courbes augmente lorsqu'on approche par en dessous la valeur critique. Nous définissons un rayon moyen pour la projection sur le plan x-y de l'application 3-d et nous montrons numériquement qu'il converge vers une constante finie pour V < 2. D'autre part, son comportement critique est analysé pour un γ égal au nombre d'or. Finalement, nous discutons des résultats antérieurs sur la chaîne désordonnée

Numerical analysis of a neural network with hierarchically organized patterns

A numerical analysis of the retrieval behavior of an associative memory model where the memorized patterns are stored hierarchically is performed. It is found that the model is able to categorize errors. For a finite number of categories these are retrieved correctly even when the stored patterns are not. Instead when they are allowed to increase with the number of neurons their retrieval quality deteriorates above a critical category capacity.Nous étudions numériquement les capacités de mémoire d'un modèle de mémoire associative où les structures mémorisées sont organisées hiérarchiquement. Nous trouvons que le modèle est capable de reconnaître les classes de structures. Pour un nombre fini de classes, les catégories sont retrouvées correctement, même quand les structures mémorisées ne le sont pas. Par contre, quand le nombre de classes augmente comme le nombre de mémoires, la qualité de la mémorisation se détériore au-dessus d'un seuil critique

Organolanthanoid-halide synthons - a new general route to monofunctionalized lanthanoid(II)compounds?

New EuII and YbII complexes [Ln(Ph2pz)I(thf)4] were synthesized from the corresponding metals and 3,5-diphenylpyrazole (HPh2pz) using iodobenzene as oxidizing agent. In the absence of the pyrazole, the charge separated YbII/YbIII complex [{Yb(dme)4}{YbPh4(dme)}2] has been isolated