Siloxane Coordination Revisited: Si−O Bond Character, Reactivity and Magnificent Molecular Shapes

Siloxanes have evolved into a multi-million dollar business due to their manifold of commercial and industrial applications. As siloxanes have high hydrophobicity, low basicity, high flexibility and also high chemical inertness in common, their chemistry differs significantly from that of organic ethers. The discovery of organic crown ethers, for instance, is commonly accepted as the birth of synthetic host-guest chemistry. Regarding the chemical properties of siloxanes, cyclic siloxanes which formally resemble silicon analogues of crown ethers, have received considerably less interest in terms of their host-guest chemistry. Hence, only little is known about siloxane coordination chemistry in the chemical community and the number of published works in this field has been very low till lately. In the last few years, the field has significantly advanced and elegant methods were established to enable the Si−O−Si unit for coordination. This review therefore summarizes the recent developments in the field, recapitulates the historical aspects of siloxane coordination chemistry and describes the specific Si−O bond character with regard to different siloxane linkages. Implications on Si−O bond activation are included and the limits of siloxane coordination are redefined

Tetra­carbon­yl[bis­(diphenyl­phosphan­yl)tetra­methyl­disiloxane-κ2 P,P′]chromium(0)

The title compound, [Cr(C28H32OP2Si2)(CO)4], was obtained by the ligand-exchange reaction of Cr(CO)6 with (Ph2PSiMe2)2O in refluxing toluene. The CrC4P2 coordination geometry is distorted octa­hedral, with a P—Cr—P bite angle of 99.22 (4)°

The Effect of 45{\deg} Grain Boundaries and associated Fe particles on Jc and resistivity in Ba(Fe0.9Co0.1)2As2 Thin Films

The anisotropy of the critical current density Jc depends in general on both the properties of the flux lines (such as line tension, coherence length and penetration depth) and the properties of the defects (such as density, shape, orientation etc.). Whereas the Jc anisotropy in microstructurally clean films can be scaled to an effective magnetic field containing the Ginzburg-Landau anisotropy term, it is in general not possible (or only in a limited field range) for samples containing extended defects. Here, the Jc anisotropy of a Co-doped BaFe2As2 sample with 45{\deg} [001] tilt grain boundaries (GBs), i.e. grain boundaries created by 45{\deg} in-plane rotated grains, as well as extended Fe particles is investigated. This microstructure leads to c-axis correlated pinning, both due to the GBs and the Fe particles and manifests in a c-axis peak in the Jc anisotropy at low magnetic fields and a deviation from the anisotropic Ginzburg-Landau scaling at higher fields. Strong pinning at ellipsoidal extended defects, i.e. the Fe particles, is discussed, and the full Jc anisotropy is fitted successfully with the vortex path model. The results are compared to a sample without GBs and Fe particles. 45{\deg} GBs seem to be good pinning centers rather than detrimental to current flow.Comment: 8 pages, 7 figures, CEC-ICMC 2013 proceeding, accepted for publication in Advances in Cryogenic Engineering (Materials

Inhalt und Struktur der Datenbank "Wahl- und Sozialdaten der Kreise und Gemeinden des Deutschen Reiches von 1920 bis 1933"

This article describes the content of a very large historical data bank about the Weimar Republic and the principles of data-management, analogous to the hierarchical systematic structure of its underlying statistical sources. The subjects of the data bank are the Kreise (counties) and Gemeinden (communities) with their electoral results of eight Reichstagswahlen and census data about social occupation structure, confession and unemployment in the period between 1920 and 1933. Some important problems would appear, when using this cross-sectional organized aggregate data set for longitudinal purposes. The solutions of this problems base upon several strategies in conjunction with special code variables, established by the author into the data bank. They produce new longitudinal data sets with relative stable geographic units. Further, this article gives a short view about the variables and technical aspects of data-handling. The historical data bank and a user manual is now public for social and historical scientists and available via the Center for Historical Social Research in Cologne/FRG