Synthesis of periphery-functionalized dendritic molecules using polylithiated dendrimers as starting material

A general method for the functionalization of Si-Cl terminated carbosilane dendritic molecules via organolithium or organomagnesium reagents is described. Quantitative exchange of the bromine atoms of 4-bromophenyl-functionalized dendrimers affords polylithiated species that are valuable starting materials for further functionalization, e.g., into pyridyl alcohols. The latter were successfully applied as catalyst precursors in a ruthenium-mediated ring-closure metathesis reaction.     

On the relation of the vacancy formation parameters and the Gruneisen constant in metals

By using the Swenson formula, for the pressure derivative of the bulk modulus, and the Slater formulation for the Gruneisen constant a simple useful relation between the vacancy-formation entropy and the Gruneisen constant is derived in the case of metals. This relation also indicates that actually a close correlation between the vacancy-formation enthalpy, the coefficient of the volume expansivity and the corresponding melting point exists.     

The formation volume of Frenkel defect in silver halides

The formation volume ν_f of a (cation) Frenkel Defect is calculated in AgCl and AgBr. The proposed formula for ν_f has no adjustable parameters and contains the formation enthalpy (of a Frenkel defect), the compressibility of the solid at absolute zero and the pressure derivative of the compressibility. The calculated values are in good agreement with the experimental results.     

Oscillatory melting temperature of the vortex smectic phase in layered superconductors

We report on transport measurements of YBa 2Cu 3O (7-delta) single crystals with different oxygen contents in the geometry B, J ||ab (J perpendicularB). Our data show that the vortices become confined between the Cu-O planes below a well-defined temperature at which the effective size 2xi of the vortex core is approximately equal to the period of the Cu-O layers. This confinement strongly increases the vortex liquid freezing temperature. A new melting line is found separating a vortex liquid and a smectic phase, which shows an oscillatory field dependence reflecting differences between commensurate and incommensurate smectic states.     

Connection of activation volume and activation enthalpy with the bulk properties in olivine, LiBr and CsCl

The activation volume V^act has been measured for olivine, LiBr and CsCl. It is shown that the quantity V^act/H^act, where H^act denotes the activation enthalpy, is governed by the elastic properties of the bulk material in accordance to a model suggested by Varotsos and Alexopoulos. An explanation of the latter model for the migration process is attempted by means of the ballistic model independently suggested by Van Vechten.     

Synthesis of Novel Chiral Diol Ligands for the Enantioselective Reactions

The chiral diols ((,(,((,((-Tetraaryl-1,3-dioxolane-4,5-dimethanols) have been used for the formation of cyclic titanates and similar derivatives of Mg, Al and Zr. These complexes of oxophilic metal centers were employed in catalytic and stiochiometric enantioselective reactions such as enantioselective addition reactions of carbon-centered nucleophiles to aldehydes1, [2+2] cycloadditions2, and Diels-Alder reactions3. So far, the two hydrogen atoms of all this type of diols are in trans form…     

The diffraction of elastic waves by an imperfect fusion bond

We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material.     

New aspects on the dielectric properties of the alkali halides with divalent impurities

Dielectric losses were measured in the following crystals NaCl+ (Mg²⁺, Co²⁺, Ni²⁺, Sr²⁺, Ca²⁺, Mn²⁺, Zn²⁺, Cd²⁺, Ba²⁺, Pb²⁺), KCl + (Ca²⁺, Sr²⁺, Ba²⁺, ²⁺, Pb²⁺) and KBr + (Sr²⁺, Ba²⁺) in the frequency region 5–500 kHz. It was found that when the divalent cation impurity has an electronic configuration similar to the inert gases (1) no observable deviation from simple Debye theory exists (2) the activation energy Φ increases linearly with the ionic radius of the impurity.The above observations (1) and (2) do not hold when the divalent cation impurity has d-electrons in the outer subshell.     

The curvature in conductivity plots of silver halides as a consequence of anharmonicity

At high temperatures the conductivity plot of silver halides shows a pronounced upward curvature to higher conductivity values. This curvature has been attributed to an excessive decrease of the Gibbs formation energy g^f per Frenkel defect. Such a decrease is known to arise from Lidiard-Debye-Huckel interactions and expansivity. However a quantitative evaluation for AgCl and AgBr has shown that the said effect is not sufficient to explain the experimental data. The present paper proposes a further reason for the excessive decrease of g^f; it is due to an excessive fall of the bulk modulus B at temperatures near the melting point. For AgCl a fall by approx. 10% would give the needed decrease of g^f.