Film flow over strongly undulated bottom profiles at low Reynolds numbers – Experimental study

We study gravity driven films of a Newtonian fluid flowing down sinusoidal bottom profiles. We give experimental evidence of vortices in the film flow under creeping flow conditions down to Reynolds numbers of the order of 10^–5. The vortices are created in the valleys of the undulated bottom profile. They are visualized employing a particle image velocimeter with fluorescent tracers. It turns out that the vortices are generated beyond a critical film thickness.     

Thermally induced Lengthening of weak Dative Bonds in Donor Functionalized Organoaluminum Alkoxides observed by X‐ray Single Crystal Diffraction

The length of weak dative bonds in donor functionalized organo aluminum alkoxides [R₂Al—O—R'—Y]₂ (Y = NR₂, OR, SR) show a temperature dependence in the solid state that is distinctively different from the common effect of libration. This observation is interpreted as being caused by thermal excitation. The possible general relevance of this phenomenon for the study of very weak bonds in molecular systems is discussed.     

Chemische und cyclovoltammetrische Untersuchung der Redoxreaktionen der Decahalogendecaborate closo‐[B10X10]2– und hypercloso‐[B10X10]· – (X = Cl,Br). Kristallstrukturanalyse von Cs2[B10Br10] · 2 H2O

Chemical and Cyclovoltammetric Investigation of the Redoxreactions of the Decahalodecaborates closo ‐[B₁₀X₁₀]^2– and hypercloso ‐[B₁₀X₁₀]^{· –} (X = Cl, Br)¹⁾. Crystal Structure Analysis of Cs₂[B₁₀Br₁₀] · 2 H₂O The oxidation of the decachloro‐closo‐decaborates(2–) Cs₂[B₁₀Cl₁₀] or [Me₄N]₂[B₁₀Cl₁₀] with Tl(CF₃COO)₃ leads to the corresponding radical monoanion hypercloso‐[B₁₀Cl₁₀] ^{· –}, which was characterized by ESR and UV/Vis spectroscopy. [B₁₀Cl₁₀] ^{· –} does not dimerize like [B₁₀H₁₀] ^{· –} but it is reduced by acetonitrile to the dianion [B₁₀Cl₁₀]^2–. Cs₂[B₁₀Cl₁₀] reacts with stronger oxidation agents like CoF₃ (in dichloromethane) or XeF₂ (in perfluorhexane), respectively, to yield B₉Cl₉ and, in traces, B₈Cl₈. In opposite to this, the decabromoderivative Cs₂[B₁₀Br₁₀] does not show any reaction with Tl(CF₃COO)₃ in acetonitrile or with CoF₃ in CH₂Cl₂. The oxidation of the dianions [B₁₀X₁₀]^2– (X = Cl, Br) was studied by electroanalytical methods (cyclic voltammetry, chronoamperometry, chronocoulometry). Formal potentials were determined for the two steps of the reaction, which do not seem to be affected by structural rearrangements. The crystal structure of Cs₂[B₁₀Br₁₀] · 2 H₂O was analyzed by single‐crystal X‐ray diffraction. Cs₂[B₁₀Br₁₀] · 2 H₂O crystallizes monoclinic (space group I2/a, (no. 15), Z = 8, a = 1361.54(9) pm, b = 1215.89(5) pm, c = 3108.4(2) pm, α = 90°, β = 97.916(8)°, γ = 90°). The closo‐cluster B₁₀Br₁₀^2– has a bicapped square antiprismatic structure with idealized D_4d symmetry.     

Neubestimmung der Kristallstruktur von NbOCl3

NbOCl₃ was obtained from a reaction of NbCl₅ and Nb₂O₅ at 260?C. Contrary to the literature data, NbOCl₃ crystallizes in the non‐centrosymmetric space group P&4macr;2₁m as determined by single‐crystal and powder X‐ray diffraction data (crystal: a = b = 1089.59(6) pm, c = 394.79(2) pm, Z = 4, R₁ = 0.0229, wR₂ = 0.0459, powder: a = b = 1086.36(6) pm, c = 393.65(2) pm). The niobium atoms are surrounded by distorted octahedra built of four chlorine atoms and two oxygen atoms in trans positions. Two such octahedra are edge‐bridged through shared chlorine atoms, forming dimers. These units are linked to each other by apical oxygen atoms forming one‐dimensional Nb₂Cl₆O₂ chains parallel [001]. Contrary to the literature data two different Nb‐O distances are obtained.     

[{Cp*(OC)2Re}2(μ‐POH)], ein Zweikernkomplex mit einem verbrückenden Hydroxiphosphiniden‐Liganden

[{Cp*(OC)₂Re}₂(μ‐POH)], a Dinuclear Complex with a Bridging Hydroxiphosphinidene Ligand The reaction of [{Cp*(OC)₂Re}₄(μ₄‐η¹ : η¹ : η¹ : η¹‐P₂)] ( 1 ) with 0.1 m HCl gives [{Cp*(OC)₂Re}₂(μ‐POH)] ( 2 ), the X‐ray crystal structure of which reveals a dinuclear rhenium complex with a μ‐POH (hydroxiphosphinidene) ligand.     

Ethylene polymerization using crosslinked polystyrene as support for zirconocene dichloride/methylaluminoxane

In this paper we report on a zirconocene dichloride/methylaluminoxane catalyst system supported on a crosslinked polystyrene in order to provide ethylene polymerization catalysts for gas phase or slurry processes. Our novel approach uses the Diels‐Alder reaction of cyclopentadiene functions as the final, cross‐linking synthetic step. This provides polymer supported zirconocene catalysts with a homogeneous distribution of active sites. The catalysts were shown to be highly active and to form spherical beads as proven by scanning electron microscopy.     

Evidence for the preservation of the particle identity in miniemulsion polymerization

A combination of small‐angle neutron scattering (SANS), conductivity, and surface tension measurements is used to show that the primary droplets in miniemulsion polymerization have the same size and the same size distribution as the final particles. It is also shown that hexadecane employed as a cosurfactant is homogeneously dispersed in the droplets and does not possess any interface activity. The presented data support that a 1 : 1 copy from monomer droplets to polymer particles is achieved.