Metallacyclische Carboxylate des Nickels: Darstellung, Strukturen und Anwendungen in der Synthese

Im Zentrum der in dieser Arbeit vorgestellten Untersuchungen standen spezielle Organometallverbindungen des Nickels, sogenannte Nickelalactone bzw. nickelacyclische Carboxylate. Dabei wurden drei verschiedene Typen dieser Verbindungen in die Untersuchungen einbezogen

Scale Dependence of Overconfidence in Stock Market Volatility Forecasts

In this study, we analyze whether volatility forecasts (judgmental confidence intervals) are influenced by the specific elicitation mode (i.e. whether forecasters have to state future price levels or directly future returns as upper and lower bounds). We present questionnaire responses of about 250 students from two German universities. Participants were asked to state median forecasts as well as confidence intervals for seven stock market time series. Using a between subject design, one half of the subjects was asked to state future price levels, the other group was directly asked for returns. Consistent with prior research we find that subjects underestimate the volatility of stock returns, indicating overconfidence. As a new insight, we find that the strength of the overconfidence effect in stock market forecasts is highly significantly affected by the fact whether subjects provide price or return forecasts. Volatility estimates are lower (and the overconfidence bias is thus stronger) when subjects are asked for returns compared to price forecasts

Plasmon damping below the Landau regime: the role of defects in epitaxial graphene

The sheet plasmon in epitaxially grown graphene layers on SiC(0001) and the influence of surface roughness have been investigated in detail by means of low-energy electron diffraction (LEED) and electron energy loss spectroscopy (EELS). We show that the existence of steps or grain boundaries in this epitaxial system is a source of strong damping, while the dispersion is rather insensitive to defects. To the first order, the lifetime of the plasmons was found to be proportional to the average terrace length and to the plasmon wavelength. A possible reason for this surprisingly efficient plasmon damping may be the close coincidence of phase (and group) velocities of the plasmons ( almost linear dispersion) with the Fermi velocity of the electrons. Therefore, uncorrelated defects like steps only have to act as a momentum source to effectively couple plasmons to the electron-hole continuum

Pulsed Laser Deposition of quasi-multilayer superconducting Ba(Fe0.92_{0.92}Co0.08_{0.08})2As2_{2}-BaHfO3_{3} nanocomposite films

Quasi-multilayer films with perovskite nano-particles have already been investigated and reported in YBCO compounds. Here, we introduce this technique to iron based superconductors by preparing quasi-multilayer nanocomposite films of Co-doped BaFe2As2 with BaZrO3 and BaHfO3 perovskite nanoparticles by a pulsed laser deposition technique using a frequency-tripled Nd:YAG laser (λ = 355 nm) with separate targets of the constituents. We investigated the enhancement of pinning force density and critical current density in relation to critical temperature reduction. Application-relevant properties are discussed in relation to the deposition conditions and the microstructural properties of the films to better understand growth and behavior of strong pinning centers in these materials

Pulsed Laser Deposition of quasi-multilayer superconducting Ba(Fe0.92Co0.08)2As2-BaHfO3 nanocomposite films

Quasi-multilayer films with perovskite nano-particles have already been investigated and reported in YBCO compounds. Here, we introduce this technique to iron based superconductors by preparing quasi-multilayer nanocomposite films of Co-doped BaFe2As2 with BaZrO3 and BaHfO3 perovskite nanoparticles by a pulsed laser deposition technique using a frequency-tripled Nd:YAG laser (λ = 355 nm) with separate targets of the constituents. We investigated the enhancement of pinning force density and critical current density in relation to critical temperature reduction. Application-relevant properties are discussed in relation to the deposition conditions and the microstructural properties of the films to better understand growth and behavior of strong pinning centers in these materials

bis‐Silyl‐triazenide ligands in alkaline‐earth metal chemistry

Monoanionic N,N‐chelating triazenide ligands, [R‐NNN‐R]−, are compared to formamidinate or β‐diketiminate ligands considerably less electron‐donating and therefore potentially suitable for stabilizing electron rich metals in low oxidations states. A feature reported for silyl‐substituted triazenide ligands, is their ability to eliminate N2 resulting in (R3Si)2N− anions. Here we describe a series of group 1 and 2 metal complexes with the very bulky bis‐silyl‐triazenide ligand [tBu3Si‐NNN‐SitBu3]−. Heteroleptic complexes could be isolated for Mg: {[(tBu3Si)2N3]MgnBu}2 or {[(tBu3Si)2N3]MgI}2, including its ether adducts. Despite bulky silyl substituents, the ligand did not stabilize heteroleptic [(tBu3Si)2N3]AeN(SiMe3)2 complexes for Ca, Sr and Ba and only homoleptic Ae[(tBu3Si)2N3]2 complexes were isolated. Thermal decomposition of these complexes did result in N2 elimination and formation of the expected amide complexes. Reduction of [(tBu3Si)2N3]MgI ⋅ (Et2O) with KC8 in Et2O led to the formation of a MgI complex with a Mg−Mg bond length of 2.902(1) Å. As only one of the Mg centres shows coordination with a Et2O ligand, this is a rare example of an asymmetric Mg−Mg bond. This MgI complex is rather unstable in benzene solution, likely due to reduction of the ligand system. Triazenide ligands are therefore not suitable for stabilization of group 2 metals in low oxidation states. image Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165

Low‐valent Mg(I) complexes by ball‐milling

Abstract Mechanochemistry has great potential in the syntheses of low‐valent Mg(I) complexes. Magnesium iodide precursors with three different β‐diketiminate (BDI) ligands of varying bulk have been reduced with K/KI (or Na/NaCl) using the ball‐mill. Depending on the steric bulk of the ligand, the raw products are intensely colored powders, indicating the presence of (BDI)Mg⋅ radicals. Extraction with pentane gave (BDI)Mg−Mg(BDI) in excellent yields. Reaction of the powder with H2 prior to extraction gave [(BDI)MgH]2. Extraction with benzene gave (BDI)Mg(C6H6)Mg(BDI) with a dearomatized puckered benzene dianion. Ball‐milling in the presence of triphenylbenzene gave a dinuclear Mg complex with a Ph3C6H3‐dianion which slowly decomposed to (BDI)Mg−Mg(BDI) and Ph3C6H3

Structural and chemical properties of superconducting Co-doped BaFe2_2As2_2 thin films grown on CaF2_2

Thin films of Co-doped BaFe$_2$As$_2$ of similar thickness (~40 nm) were grown with different growth rates (0.4 Å s$^{-1}$ and 0.9 Å s$^{-1}$) by pulsed laser deposition on CaF$_2$(001) substrates. Analytical transmission electron microscopy (TEM) was applied to analyze the microstructure and secondary phases. The formation of BaF$_2$ and a high concentration of planar defects (mainly stacking faults) are observed for the sample grown at a low rate. A higher growth rate results in high-quality epitaxial films with only few antiphase boundaries. A higher $T_\text{c}$ was measured for the sample grown at a low growth rate, which is attributed to the difference in strain state induced by the high concentration of defects. Large crystalline Fe precipitates are observed in both samples. Chemical analysis shows a pronounced O and slight F content at the planar defects which highlights the role of O in defect formation. Electron-beam-induced irradiation damage during TEM measurements is observed and discussed