Buchbesprechungen

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Eine Methode zur Analyse sehr kleiner Monazitmengen

Zusammenfassung An natürlichen Monaziten wurde eine Methode für die MikroGesamtanalyse dieser Mineralien entwickelt. Dieser Analysengang wurde sodann, an einem künstlichen Gemenge, welches ähnlich den natürlich vorkommenden Monaziten zusammengesetzt war und lediglich von den Nebenbestandteilen etwas größere Mengen enthielt, überprüft und für ausreichend genau befunden. Für Blei jedoch wurde eine Spezialmethode ausgearbeitet, da es nicht möglich war, innerhalb des beschriebenen Gesamtanalysenganges befriedigende Bleiwerte zu erhalten.Es ist uns eine angenehme Pflicht, dem Vorstand des Instituts, Herrn Professor Dr. A. Franke, für seine wirksame Förderung unserer Arbeit unseren wärmsten Dank auszusprechen.     

Complexes of Click‐Derived Bistriazolylpyridines: Remarkable Electronic Influence of Remote Substituents on Thermodynamic Stability as well as Electronic and Magnetic Properties

2,6‐Bis(1,2,3‐triazol‐4‐yl)pyridine (btp) ligands with substitution patterns ranging from strongly electron‐donating to strongly electron‐accepting groups, readily prepared by means of Cu‐catalyzed 1,3‐dipolar cycloaddition (the “click” reaction), were investigated with regard to their complexation behavior, and the properties of the resulting transition‐metal compounds were compared. Metal–btp complexes of 1:1 stoichiometry, that is, [Ru(btp)Cl₂(dmso)] and [Zn(btp)Br₂], could be isolated and were crystallographically characterized: they display octahedral and trigonal‐bipyramidal coordination geometries, respectively, and exhibit high aggregation tendencies due to efficient π–π stacking leading to low solubilities. Metal–btp complexes of 1:2 stoichiometry, that is, [Fe(btp)₂]²⁺ and [Ru(btp)₂]²⁺, could also be synthesized and their metal centers show the expected octahedral coordination spheres. The iron compounds exhibit quite a complex magnetic behavior in the solid state including spin crossover near room temperature, and hysteresis and locking into high‐spin states on tempering at 400 K, depending on the substituents on the btp ligands. Cyclic voltammetry studies of [Ru(btp)₂]²⁺ reveal strong modulation of the oxidation potentials by more than 0.6 V and a clear linear correlation to the Hammett constant (σ_para) of the substituent at the pyridine core. Isothermal titration calorimetry was used to measure the thermodynamics of the Fe^II–btp complexation process and enabled accurate determination of the complexation enthalpies, which display a linear relationship with the σ_para values for the terminal phenyl substituents. Detailed NMR spectroscopic studies finally revealed that in the case of Fe^II complexation, dynamics are rapid for all investigated btp derivatives in acetonitrile, while replacing Fe^II by Ru^II or changing the solvent to dichloromethane effectively slows down ligand exchange. The results nicely demonstrate the utility of substituent parameters, originally developed for linear free‐energy relationships to explain reactivity in organic reactions, in coordination chemistry, and to illustrate the potential to custom‐design btp ligands and complexes thereof with predictable properties. The fast equilibration of the [Fe(btp)₂]²⁺ complexes together with their tunable stability and interesting magnetic properties should enable the design of dynamic metallosupramolecular materials with advantageous properties.     

Synthesis and antimalarial activity of new 1,2,4,5-tetroxanes and novel alkoxy-substituted 1,2,4,5-tetroxanes derived from primary gem-dihydroperoxides

A convenient synthesis of new unsymmetrically substituted 1,2,4,5-tetroxanes and novel unsymmetrical alkoxy-substituted 1,2,4,5-tetroxanes starting from primary dihydroperoxides was developed. The structure of some tetroxanes was unambiguously assigned by X-ray crystal analysis giving interesting insights in the configuration and conformation of disubstituted 1,2,4,5-tetroxanes. Some of these tetroxanes showed notable antimalarial activity in vitro.     

Dünnschichtchromatographie anorganischer Ionen. I. Trennung von Kationen

Zusammenfassung An Hand einer Reihe von Modellversuchen konnte gezeigt werden, daß man mit Tri-iso-octylamin als Laufmittel dünnschichtchromatographische Trennungen durchführen kann. Ein Ion mit einem hohen Verteilungskoeffizienten kann aus einer Mischung von Ionen mit geringem Verteilungskoeffizienten selektiv abgetrennt werden. Beispiele dafür sind die selektive Abtrennung von U⁶⁺ oder Mo⁶⁺ aus einem Gemisch von Fe, Ni, Co, Zn in salpetersaurer Lösung oder dei Abtrennung von Fe³⁺ aus (Ni²⁺, Mn²⁺, Fe³⁺)-Mischungen.

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Summary By means of a number of model trials it was shown that thin layer chromatographic separations can be made by means of tri-iso-octylamine as carrier. An ion with a high distribution coefficient can be selectively isolated from a mixture of ions with low distribution coefficients. Illustrative examples include the selective separation of U⁶⁺ or Mo⁶⁺ from a mixture with Fe, Ni, Co, Zn, in nitric acid solution or of Fe³⁺ from a mixture of Ni²⁺, Mn²⁺, Fe³⁺.

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Résumé On montre, en se servant d'une série d'expériences types, que l'on peut effectuer des séparations chromatographiques en couche mince avec la tri-isooctylanaine comme éluant. On peut séparer sélectivement un ion dont le coefficient de partage est élevé, à partir d'un mélange d'ions possédant des coefficients de partage faibles. On cite comme exemple la séparation sélective de U⁶⁺ ou de Mo⁶⁺ à partir d'un mélange de Fe, Ni, Co, Zn en solution nitrique ou la séparation de Fe³⁺ à partir de mélanges (Ni²⁺, Mn²⁺, Fe³⁺).

     

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