Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

Some reactions of copper(I) pentafluorothiophenolate as a nucleophile

Several aromatic compounds containing one or two C₆F₅S groups have been prepared by nucleophilic displacement reactions using CuSC₆F₅ in DMF solution. Aromatic iodine or bromine, rather than chlorine of fluorine is replaced by the SC₆F₅ group using CuSC₆F₅. A mechanism is postulated. New compounds prepared include $\text{p}$-(C₆F₆F₅S)₂C₆H₄, $\text{o}$- and $\text{m}$-(C₆F₅S)₂C₆F₄ and $\text{p}$XC₆H₄SC₆F₅(X=C1, NO₂, I, CH₃, CO₂C₂H₅).     

Reactions of some fluoroaromatics with the ethoxide anion

The reactions of sodium ethoxide in ethanol with various fluoroaromatics, C₆F_6?nH_n, C₆F_5?nH_nNO₂, C₆F₅X (X = CF₃, C₆F₅, COCH₃, CH₂Br), C₆Cl₆ and $\text{m}$H₂C₆Cl₄ have been studied. Partial substitution of the aromatic halogen was observed. The new products have been characterized by elemental analysis, NMR (H?1 and F?19), infrared and mass spectroscopy.     

The thiolate anion as a nucleophile Part XII. Reactions of Lead(II) Benzenethiolate

The reactions of various fluoroaromatics, C₆F_6?xH_x, and C₆F₅X (X = C₆F₆, Cl, Me, NO₂, CF₃, COCl, CH₂Br, OMe, and NH₂) with lead(II) benzenethiolate in DMF have been examined. Lead thiolate acted as an excellent source of benzenethiolate anions and displacement of fluorine, chlorine or the nitro group was observed. The new products have been characterized by elemental analysis, and NMR (H?1 and F?19), infrared and mass spectroscopy.     

Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement of gamma-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.     

Reactions of some bromofluorobenzenes with copper(I) benzenethiolate

The reactions of copper(I) benzenethiolate with some bromofluorobenzenes have resulted in the replacement of the bromine by a phenylthio group. Combinations of this method and the reactions of sodium thiolates with fluorobenzenes have enabled various isomeric phenylthio substituted fluorobenzenes C₆H_xF_y(SR)_z to be prepared. The new products have been characterized by elemental analyses, mass, infrared, and fluorine NMR spectroscopy.