Kristallographische Gruppe-Untergruppe-Beziehungen und ihre Anwendung in der Kristallchemie

Crystallographic Group-subgroup Relations and their Use in Crystal Chemistry Family trees of crystallographic group-subgroup relations are especially suited to display relationships among crystal structure types. Starting from an aristotype, a simple, highly symmetrical structure type, more and more complicated structures are obtained by reducing the space group symmetry. In doing so, it is important to keep trace of how the occupied Wyckoff positions develop from a space group to its subgroups and which coordinate transformations and origin shifts occur. The neccessary information can by obtained from the new volume A1 of International Tables for Crystallography. Possible error sources are demonstrated with the aid of examples. When a Wyckoff position is split into different symmetry-independent Wyckoff positions, substitution derivatives become possible. If the position does not split, its site symmetry must be reduced, thus rendering possible distorted derivative structures. Such distortions are of special importance in phase transitions, as shown with the examples K₂[TeBr₆], (NO)₂[TiCl₆] and SrCu₂(BO₃)₂. Phase transitions involving a symmetry reduction are likely to produce twinned crystals. This can be the cause of errors in crystal structure determinations, as shown with the example of CaMnF₅. The possible ways to occupy voids in sphere packings can be followed and calculated systematically, including the possibility to predict crystal structures. Sometimes the indices of the symmetry reduction take values that seem curious, such as 13 for CZr₆I₁₂ and 37 for PtCl₃. The systematic application is also possible to molecular packings, such as to the modifications of P₄S₃. Tetraphenylphosphonium salts often crystallize in the space group P4/n or its subgroups, retaining pseudotetragonal symmetry even in monoclinic and triclinic structures.     

Die Cochenilletinktur und ihre Anwendung in der Alkali- und Acidimetrie

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Hybrid Rhodamine Fluorophores in the Visible/NIR Region for Biological Imaging

Fluorophores and probes are invaluable for the visualization of the location and dynamics of gene expression, protein expression, and molecular interactions in complex living systems. Rhodamine dyes are often used as scaffolds in biological labeling and turn‐on fluorescence imaging. To date, their absorption and emission spectra have been expanded to cover the entire near‐infrared region (650–950 nm), which provides a more suitable optical window for monitoring biomolecular production, trafficking, and localization in real time. This review summarizes the development of rhodamine fluorophores since their discovery and provides strategies for modulating their absorption and emission spectra to generate specific bathochromic‐shifts. We also explain how larger Stokes shifts and dual‐emissions can be obtained from hybrid rhodamine dyes. These hybrid fluorophores can be classified into various categories based on structural features including the alkylation of amidogens, the substitution of the O atom of xanthene, and hybridization with other fluorophores.     

Chelometrische Arsenbestimmung und ihre Anwendung auf die Mikro-Elementaranalyse

Zusammenfassung Mikromengen Arsenit und/oder Arsenat werden mit Silbernitrat gefällt. Der Niederschlag wird in Tetracyanonickelat gelöst und das freigesetzte Nickel mit ÄDTA gegen Murexid titriert. Chlorid, Bromid, Jodid und Phosphat stören. Nach dieser Methode wurde Arsen in organischen Substanzen im Anschluß an eine Schöniger-Verbrennung bestimmt.

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Summary Micro quantities of arsenite and/or arsenate are precipitated with silver nitrate. The precipitate is dissolved in tetracyanonickelate and the demasked nickel is titrated with EDTA in the presence of murexide. Chloride, bromide, iodide, and phosphate interfere. Arsenic was determined by this method in organic compounds subsequent to aSchöniger combustion.

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Résumé On précipite des microquantités d'arsénites et/ou d'arséniates par le nitrate d'argent. On dissout le précipité dans le nickelotétracyanure et l'on titre le nickel libéré par l'EDTA en présence de murexide. Les chlorures, bromures, iodures et phosphates gênent. On a dosé suivant cette méthode l'arsenic dans les substances organiques après une combustion suivantSchöniger.

     

Asymmetrische diorganoalkoxyzinnhydride und ihre anwendung als stereoselektive reduktionsmittel

The asymmetric diorgano(alkoxy)tin halides RR′Sn(OC₁₀H₁₉)X and RR′Sn-(OC₁₀H₁₇)X were synthesized by the reaction of diorganotin halides with sodium l(?)mentholate and sodium l(?)borneolate. Reduction of these asymmetric diorgano(alkoxy)tin halides yields the optically active diorgano(alkoxy)tin hydrides RR′Sn(OC₁₀H₁₉)H and RR′Sn(OC₁₀H₁₇)H, which are used for the asymmetric reduction of racemic haloalkanes.     

Die komplexometrische Wismutbestimmung und ihre Anwendung auf die Arzneimittelanalyse

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