High-pressure synthesis and structures of lanthanide germanides of LnGe5 (Ln=Ce, Pr, Nd, and Sm) isotypic with LaGe5

A series of lanthanide penta-germanides LnGe₅ (Ln=Ce, Pr, Nd and Sm) has been prepared by high-pressure (5–13 GPa) and high-temperature (500–1200 °C) reaction. CeGe₅ crystallizes in an orthorhombic unit cell (S.G. Immm (71)) with a=4.000(5) Å, b=6.192(5) Å, c=9.86(1) Å, and V=244.1(5) Å³. The new germanides are isotypic with LaGe₅ consisting of a Ge covalent network with tunnels where guest ions Ln³⁺ are situated. The network is composed of sublayers with edge-sharing Ge six-membered rings with only boat conformation. The sublayers are connected by rare eight-coordinated Ge atoms. The cell volume of the compounds systematically decreases from La to Sm compounds, except for CeGe_5, owing to the lanthanide contraction. The lattice constants of CeGe₅ are smaller than those of the Pr compound because it contains Ce⁴⁺ ions. CeGe₅ is paramagnetic above 2 K, but does not obey the Curie–Weiss law. PrGe₅ and NdGe₅ are Curie–Weiss type paramagnets with Weiss temperatures of –3.3 and –18.4 K. SmGe₅ shows an antiferromagnetic transition at 10.4 K.     

Aggregations or crystals of Acridine Orange in various synthetic-polymer fibres

Summary The visible absorption spectra of the cross-sections of the dyed various synthetic-polymer fibres were measured by means of a microspectrophotometer. We found that the spectra of Acridine Orange hydrochloride in the crosssections of fibres showed a maximum of -band and band, and the spectra of Acridine Orange (free base), indicated a maximum of -band, -band and the crystal peak of the dye. These results suggest that the monomeric state, the aggregate as well as the crystal of the dye exist in these dyed synthetic-polymer fibres.

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Zusammenfassung Die sichtbaren Absorptionsspektren der Querschnitte der verschiedenen gefärbten synthetischen Polymerfasern wurden mit einem Mikrospektrophotometer gemessen. Dabei wurde herausgefunden, daß die Spektra der Acridinorange Hydrochloride in den Querschnitten ein Maximum beim -Band und beim -Band und die Spektra der Acridinorange (freie Base) ein Maximum beim -Band, -Band und beim Kristallpik der Farbstoffe zeigen. Diese Resultate deuten darauf hin, daß sowohl der monomere Status, als auch Aggregate und die Kristalle der Farbstoffe in diesen synthetischen Polymerfasern existieren.

     

Highly Mesoporous Metal-Organic Frameworks as Synergistic Multimodal Catalytic Platforms for Divergent Cascade Reactions

Rational engineering and assimilation of diverse chemo- and biocatalytic functionalities in a single nanostructure is highly desired for efficient multistep chemical reactions but has so far remained elusive. Here, we design and synthesize multimodal catalytic nanoreactors (MCNRs) based on a mesoporous metal-organic framework (MOF). The MCNRs consist of customizable metal nanocrystals and stably anchored enzymes in the mesopores, as well as coordinatively unsaturated cationic metal MOF nodes, all within a single nanoreactor space. The highly intimate and diverse catalytic mesoporous microenvironments and facile accessibility to the active site in the MCNR enables the cooperative and synergistic participation from different chemo- and biocatalytic components. This was shown by one-pot multistep cascade reactions involving a heterogeneous catalytic nitroaldol reaction followed by a [Pd/lipase]-catalyzed chemoenzymatic dynamic kinetic resolution to yield optically pure (>99 % ee) nitroalcohol derivatives in quantitative yields.     

Atomic Force Microscopy Study of Ultrafine Particles Prepared in Reverse Micelles

The imaging of ultrafine Au, Pd, CdS, and ZnS particles prepared in reverse micelles has been studied by atomic force microscopy (AFM). Mica substrates, derivatized with a monolayer of amine or thiol-terminated silanes, were used to immobilize the particles. The substrates were exposed to reverse micellar solutions containing the particles and were then immersed in appropriate solvent media to remove surfactants. This resulted in a partial coating of the surfaces by the particles. The particle size was estimated as the height of protrusion, shown on the AFM images. The size values for the Pd and CdS particles, thus obtained, were found to be almost identical to those obtained by transmission electron microscopy (TEM), whereas those for the Au and ZnS particles were larger than those obtained by TEM. Scanning electron microscopy showed that the Au particles tended to aggregate on the surfaces, while Pd particles were isolated from one another. Copyright 2000 Academic Press.