Komplexbildung und extraktion von zinn mit potentiel dreizähnigen dianionischen ligandenComplex formation and liquid-liquid extraction of tin with potentially tridentate dianionic ligands

Pulse polarography was used to study the extraction of tin(IV) from chloride solution with potentially tridentate dianionic ligands under unbuffered conditions. The ligands usually contained enolizable groups or were produced by splitting heterocyclic rings. The most favourable extractant was 2-(2′-hydroxyphenyl)-quinolin-8-ol, which extracted tin in the pH region 2–8; all othe rligands gave good extraction only at pH 6–8. In the organic phase, 1:1 chelates are formed in all cases. The composition of the complexes was also proved by the isolation of the solid compounds. These complexes were characterized by their Mössbauer parameters.     

Hexagonal Si−Ge Class of Semiconducting Alloys Prepared by Using Pressure and Temperature

Multi-anvil and laser-heated diamond anvil methods have been used to subject Ge and Si mixtures to pressures and temperatures of between 12 and 17 GPa and 1500–1800 K, respectively. Synchrotron angle dispersive X-ray diffraction, precession electron diffraction and chemical analysis using electron microscopy, reveal recovery at ambient pressure of hexagonal Ge−Si solid solutions (P6₃/mmc). Taken together, the multi-anvil and diamond anvil results reveal that hexagonal solid solutions can be prepared for all Ge−Si compositions. This hexagonal class of solid solutions constitutes a significant expansion of the bulk Ge−Si solid solution family, and is of interest for optoelectronic applications.     

Palladium‐Catalyzed Direct C2‐Arylation of an N‐Heterocyclic Carbene: An Atom‐Economic Route to Mesoionic Carbene Ligands

Blocking the C2 position of an imidazole‐derived classical N‐heterocyclic carbene (NHC) with an aryl group is an essential strategy to establish a route to mesoionic carbenes (MICs), which coordinate to the metal via the C4 (or C5) carbon atom. An efficient catalytic route to MIC precursors by direct arylation of an NHC is reported. Treatment of 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene (IPr) with an aryl iodide (RC₆H₄I) in the presence of 0.5 mol % of [Pd₂(dba)₃] (dba=dibenzylideneacetone) precatalyst affords the C2‐arylated imidazolium salts {IPr(C₆H₄R)}I (R=H, 4‐Me, 2‐Me, 4‐OMe, 4‐COOMe) in excellent (up to 92 %) yields. Treatment of {IPr(C₆H₅)}I with CuI and KN(SiMe₃)₂ exclusively affords the MIC–copper complex [(IPrPh)CuI].     

Comparative evaluation of labelling patterns and turnover of lipids,tagged by 15 /p-123I-phenyl-/ pentadecanoic and 1-14C-palmitic acid

Uptake and turnover of chloroform/methanol extractable tissue lipids labelled in vivo simultaneously with 15/p-¹²³I-phenyl-/pentadecanoic and l-¹⁴C-palmitic acid were compared. Lipid turnover studies were performed in fasted pentobarbital-anaesthetized Wistar rats in tissues with highly varying free fatty acid turnover rates. In all tissues investigated, i.e. heart, lung, liver, spleen and kidneys, both tracers labelled nearly identical lipid fraction. Main tracer uptake was found in free fatty acids, phospholipids, diglycerides and triglycerides. A highly significant correlation of uptake and turnover in main tissue lipid fraction indicated an essentially identical metabolic pathway of both tracers in intermediary tissue lipid metabolism. Concordant tracer uptake and turnover patterns in tissue of lipids with highly varying free fatty acid metabolic rates suggested that intrinsic metabolic activity of the tissue and respective lipid fraction was the major determinant of metabolic handling of both iodophenyl fatty- and palmitic acid. Thus, the feasibility of iodophenylpentadecanoic acid as free fatty acid tracer for studying tissue lipid metabolism is demonstrated.     

Characterization of a ferromagnetic porous silicon-based Ni/Si nanocomposite with a novel strong high-field anisotropy

Ferromagnetic (Ni) filaments are embedded into a porous silicon template by an electrochemical deposition process. During cathodic deposition using NiCl₂ as electrolyte the channels of the meso-/macroporous silicon structure are filled with metallic Ni. The resulting nanocomposite system consists of silicon as base material as well as of implemented Ni-structures, especially of highly oriented Ni-wires perpendicular to the surface showing an exceptionally high aspect ratio (>300) and is of interest for applications in microtechnology. The length of the Ni-wires is in the range of a few tens of micrometers. Concomitant with the growth of wires, spheres or ellipsoidally shaped particles are formed during the Ni-filling procedure, whose spatial frequency and distribution become tunable. Structural investigations of this system, using SEM and EDX as well as investigations of the magnetic behaviour using SQUID-magnetometry, demonstrate the dependency of the magnetic properties on the filling status of the samples. The hysteresis loops in the low-field regime up to 500 Oe as well as magnetization curves in the high-field range of a few tesla display a strong magnetic anisotropy due to magnetic rearrangements. At fields around 5 T, a decline of the magnetization followed by a steep increase is observed. This magnetic field-induced anisotropy depends on the detailed growth of the Ni within the pores which can be controlled by the deposition process. It is governed by yet unknown antiferromagnetic exchange between the wires, and inherently connected with the shape of the magnetic nano-objects.     

Directly modulated DBR lasers for long-haul transmission at 1.7 Gbit/s

Abstract

We demonstrate 1.7 Gbit/s transmission through 257 km of conventional fiber using directly modulated distributed-Bragg reflector (DBR) lasers and fiber amplifiers. This experiment resulted in a record bit rate distance product of 437 km Gb/s for direct modulation at rates between 1 and 3 Gbit/s. This paper has been accepted for presentation at OFC '92.