Stereospecific polymerization of isobutyl vinyl ether. III. Polymerization with VCl3 • LiCl

The polymerization of isobutyl vinyl ether by vanadium trichloride in n-heptane was studied. VCl₃ ? LiCl was prepared by the reduction of VCl₄ with stoichiometric amounts of BuLi. This type of catalyst induces stereospecific polymerization of isobutyl vinyl ether without the action of trialkyl aluminum to an isotactic polymer when a rise in temperature during the polymerization was depressed by cooling. It is suggested that the cause of the stereospecific polymerization might be due to the catalyst structure in which LiCl coexists with VCl₃, namely, VCl₃ ? LiCl or VCl₂ ? 2LiCl as a solid solution in the crystalline lattice, since VCl₃ prepared by thermal decomposition of VCl₄ and a commercial VCl₃ did not produce the crystalline polymer and soluble catalysts such as VCl₄ in heptane and VCl₃ ? LiCl in ether solution did not yield the stereospecific polymer. It was found that some additives, such as tetrahydrofuran or ethylene glycol diphenyl ether, to the catalyst increased the stereospecific polymerization activity of the catalysts. Influence of the polymerization conditions such as temperature, time, monomer and catalyst concentrations, and the kind of solvent on the formed polymer was also examined.     

Über krystallinische Verbindungen von Chlorcalcium mit Alkoholen

Ohne ZusammenfassungZum Schlusse sei mir gestattet, meinem hochverehrten Lehrer, Herrn Professor A. Lieben, der mir den Impuls zu dieser Arbeit gegeben, und ausserdem mir seinen gütigenRath und freundlichen Beistand stets in zuvorkommendster Weise zu Theil werden liess, meinen innigsten Dank auszusprechen.     

Thiophenylazobenzene: An Alternative Photoisomerization Controlled by Lone-Pair⋅⋅⋅π Interaction

Azoheteroarene photoswitches have attracted attention due to their unique properties. We present the stationary photochromism and ultrafast photoisomerization mechanism of thiophenylazobenzene (TphAB). It demonstrates impressive fatigue resistance and photoisomerization efficiency, and shows favorably separated (E)- and (Z)-isomer absorption bands, allowing for highly selective photoconversion. The (Z)-isomer of TphAB adopts an unusual orthogonal geometry where the thiophenyl group is perfectly perpendicular to the phenyl group. This geometry is stabilized by a rare lone-pair⋅⋅⋅π interaction between the S atom and the phenyl group. The photoisomerization of TphAB occurs on the sub-ps to ps timescale and is governed by this interaction. Therefore, the adoption and disruption of the orthogonal geometry requires significant movement along the inversion reaction coordinates (CNN and NNC angles). Our results establish TphAB as an excellent photoswitch with versatile properties that expand the application possibilities of AB derivatives.     

Progress in Polyarsolyl Chemistry

The synthesis of heteroatom analogues of the cyclopentadienyl anion Cp^? is a fascinating and challenging field of research. The replacement of methine moieties by phosphorus is well investigated for the synthesis of mono‐, tri‐ and pentaphospholyl ligands. On the other hand, arsenic derivatives are rare and 1,2,4‐triarsolyl and tetraarsolyl salts are unknown. Herein, we report on the synthesis of Cs[E₃C₂(trip)₂] ( 1 a : E=P; 1 b : E=As; trip=2,4,6‐triisopropylphenyl) and Cs[E₄C(trip)] ( 2 a : E=P; 2 b : E=As). Compound 1 b represents the first 1,2,4‐triarsolyl and 2 b the first tetraarsolyl anion. All salts are obtained in one‐pot syntheses using E(SiMe₃)₃, 2,4,6‐triisopropylbenzoyl chloride and CsF. The products 1 a ?2 C₄H₈O₂, 2 a ?Et₂O and 2 b ?3 C₄H₈O₂ were characterized by X‐ray structural analysis, which revealed planar heterocycles. Nucleus‐independent chemical shifts (NICS) confirmed the aromaticity of these anions. Notably, compound 2 a ?Et₂O is only the second tetraphospholyl ligand which is structurally characterized.     

Morphology-dependent photoluminescence property of red-emitting LnOCl:Eu (Ln=La and Gd)

Three different synthetic methods, the liquid phase process in HCl solution, the solvothermal reaction, and the surfactant-assisted solvothermal reaction, were explored to selectively control the particle shape and to enhance the luminescence intensity of the PbFCl-type red-emitting oxychloride phosphors LnOCl:Eu (Ln=La and Gd). The solvothermal pressure facilitated the low-temperature crystallization of the rod-shape particles for both Ln=La and Gd. It is noted that LaOCl:Eu nanorods show highly porous particle surface and quite low photoemission intensity. In contrast, the solvothermal synthesis could highly enhance the red-emission of GdOCl:Eu with no porous surface so as to be comparable to that of commercial Y₂O₃:Eu phosphor. An addition of surfactant material during solvothermal reaction yielded a rhomboidal-shape phosphor particles with no porous surface for both Ln=La and Gd. Interestingly, the elimination of surface porosity by using a surfactant significantly increased the emission intensity of LaOCl:Eu. It is proposed that the application of solvothermal technique for the synthesis of the PbFCl-type oxychloride phosphors is very effective to selectively control the particle shape and consequently to enhance the photoemission intensity if we use an appropriate surfactant material.     

Pressure and temperature dependence of the electric field gradient (EFG) in CdS

Using the time differential perturbed angular correlation technique (TDPAC), the electric hyperfine interaction of¹¹¹Cd in the II-VI-semiconductor CdS was investigated. The results of the temperature and pressure dependence of the electric field gradient (EFG) are discussed. The binding energyE _b for¹¹¹In at a Cd lattice site and a Cd vacancy (¹¹¹In_Cd–V_Cd–pair) could be estimated to 340 meV±80 meV by means of an Arrhenius-Plot. The disappearance of the 79 MHz and 73 MHz frequencies under a pressure of about 30 kbar could be due to their vacancy character or to the beginning of the phase transition to rocksalt structure.     

An internally heated composite gasket for diamond-anvil cells using the pressure-chamber wall as the heating element

The implementation of a heating element to a composite gasket for high-temperature applications in the diamond-anvil cell was developed based on a double-gasket assemblage. The heating element is a thin platinum wall that covers the central borehole of the metal–ceramic–metal composite gasket and interconnects the two metal component parts of the gasket. Applying electric powers up to 35 W to the two gasket metal components result in ring-like heating around the sample inside the pressure chamber with temperatures exceeding ～2000 K in individual cases. The ring-like distribution of the maximum temperature located at the pressure-chamber wall facilitates a homogeneous temperature distribution at the sample position. As a consequence of the concentration of the heating power to the pressure chamber region, gradients of surface temperatures, both at the gasket and the diamond anvil, appear to be more pronounced compared with those known for classical external electrical heating. Apart from the tests of the mechanical stability on high-pressure operation in the diamond anvil cell at room temperature, the influence of the anvils in contact with the gasket on the characteristic power–temperature curves, temperature gradients and thermal equilibration resulting from changes in electrical power settings have been evaluated within the scope of a series of experimental investigations.