Semicarbazones and thiosemicarbazones,XII: Crystal structure of salicylaldehyde semicarbazone

Summary The crystal and molecular structure of salicylaldehyde semicarbazone was obtained by single crystal X-ray diffraction. The O atom of the semicarbazone fragment isanti to the N atom of the hydrazinic group. The distribution of bond lengths in the semicarbazone fragment indicates delocalization of the -electrons. The crystal structure is stabilized by intra- and intermolecular hydrogen bonds.

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Semicarbazone und Thiosemicarbazone, 12. Mitt.: Die Kristallstruktur des Salicylaldehyd-Semicarbazons

Zusammenfassung Die Kristallstruktur und die molekulare Struktur des Salicylaldehyd-Semicarbazons wurde über Einkristall-Röntgenstreuung ermittelt. Das O-Atom des Semicarbazonteils stehtanti zum N-Atom der Hydrazin-Gruppierung. Die Bindungslängen in der Semicarbazoneinheit zeigen eine Delokalisierung der -Elektronen an. Die Geometrie der Verbindung wird durch stabilisierende intra- und intermolekulare Wasserstoffbrückenbindungen bestimmt.

     

Structural study of copper-nickel aluminate (CuxNi1−xAl2O4) spinels

CuAl₂O₄, NiAl₂O₄, and three ternary spinels Cu_xNi_1?xAl₂O₃ have been prepared, in polycrystalline form, by solid-state reaction of mixtures of CuO, NiO, and Al₂O₃ at 1223 K. X-Ray powder diffractometry, coupled with adequate computational methods, allowed determination of the unit-cell length, oxygen positional parameter, and cation distribution for each compound. Interdependence of these structural parameters is closely analyzed on the ternary oxide spinels. The one-electron difference between the Cu²⁺ and Ni²⁺ ions was found to be enough to render them distinguishable by X-ray powder diffraction.     

Asymmetry and magnetism in bis(oximato)-bridged heterobimetallic compounds: a computational approach

A density functional study of exchange coupling was carried out for a series of heterobinuclear oximato-bridged transition metal complexes. Model calculations were used to examine the influence of the electronic configuration of the metal atoms on the coupling constants. This analysis was complemented by a study of the variation of the coupling constant with the most usual structural distortions within this family of compounds. The influence of the nature of the terminal ligands as well as that of the symmetry on the bridge were also investigated.     

PPP-Berechnungen und Vergleich der Elektronenspektren von iso-π-elektronischen Sauerstoff-, Stickstoff-, Schwefel- und Selenheterocyclen

Zusammenfassung 42 Heterocyclen, die sich formal von alternierenden und nichtalternierenden Kohlenwasserstoffen durch Ersatz einer Doppelbindung durch die Heteroatome Sauerstoff, Stickstoff, Schwefel und Selen ableiten, werden nach dem Pariser-Parr-Pople-Verfahren berechnet und ihre Spektren im nahen Ultraviolett und Sichtbaren beschrieben. Schwefel und Selen werden dabei im LCAO-MO-Verfahren nach dem p-Modell behandelt. In den meisten Fällen können die Berechnungen nicht nur die spektralen Charakteristika gut wiedergeben, sondern auch Beziehungen in den Spektren iso--elektronischer Verbindungen gleicher Struktur verständlich machen. Berechnungen an kationischen Stickstoffheterocyclen führten dann zu falschen Ergebnissen, wenn die Stickstoffparameter vom Pyrroltyp übernommen werden.

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PPP-calculations and comparison of electronic spectra of iso--electronic oxygen, nitrogen, sulfur, and selenium heterocycles

42 heterocyclic compounds, formally derived from alternant or nonalternant hydrocarbons by replacing a C=C group by an oxygen, nitrogen, sulfur or selenium atom, are studied by the Pariser-Parr-Pople-type of calculation. By means of these results the near ultraviolet and visible spectra are described. The sulfur and the selenium atoms are treated in the LCAO-MO-method using the p-model. In most cases spectral features are not only well reproduced, but interrelations of the spectra of iso--electronic compounds, possessing analogous structures are interpreted, too. On calculating cationic nitrogen heterocycles using parameters of pyrrol type nitrogen results are unsatisfactory.

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Résumé 42 composés hétérocycliques, formellement dérivés d'hydrocarbures alternants ou non alternants par remplacement d'un groupement C=C par un atome d'oxygène, d'azote, de soufre ou de sélénium, sont étudiés par la méthode de Pariser-Parr-Pople. Les résultats obtenus permettent de décrire le spectre U.V. proche et visible. Soufre et sélénium sont traités en utilisant le modèle p. Dans la plupart des cas les caractères spectraux sont non seulement correctement reproduits, mais les relations entre les spectres des composés iso--électroniques à structures analogues peuvent être interprétées. Les calculs concernant les heterocycles à azote cationique sont insatisfaisants lorsqu'ils sont effectués avec des paramètres de l'azote du type pyrrole.

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Anmerkung: Die Arbeit wurde in dem von Prof. Dr. R. Mayer geleiteten Schwefelarbeitskreis der TU Dresden durchgeführt.     

Multilayered Cu–Ti deposition on silicon substrates for chemiresistor applications

Abstract

On the perspective to develop CuO–TiO₂ MOS, multilayered Cu and Ti thin layers were alternatively deposited on silicon wafers using 25?keV Ar?+?ion beam sputtering and, subsequently, oxidized by thermal annealing in air at 400?°C for 24?h. The deposited films have variable ratios of the Cu and Ti % at. One of the main goal is to obtain such multilayers avoiding the presence of Cu–Ti–O compounds. The samples were characterized in terms of composition (by RBS and SIMS analyses) and morphology (by AFM and SEM investigations). In particular, SIMS maps allows to observe the spatial distribution and thickness of each phase of the Cu/Ti multilayers, and further to observe Cu diffusion and mixing with Ti, as well as phase separation of CuO and TiO₂ in the samples. The reasons of this effect represent an open issue that has to investigated, in order to improve the MOS fabrication.     

Validation of the thermodynamic model of inorganic arsenic in non polluted river waters of the Basque country (Spain)

The thermodynamic model of inorganic arsenic was validated by comparing the predicted As(III) concentration with the experimentally determined one in several river waters samples of the Basque Country (Spain) collected in two sampling campaigns: spring and autumn 2000. This model takes into account the acid-base equilibria of As(III) and As(V) together with the redox equilibria between the H₃AsO₃ and H₃AsO₄ species. A correct prediction of As(III) concentration requires the knowledge of the total concentration of arsenic, pH, redox potential (referred to hydrogen electrode), and ionic strength values of the solution. The estimation of the activity coefficients of the arsenic species was performed by means of the Modified Bromley’s Methodology (MBM).In order to perform the experimental As(III) determination, an analytical method was implemented by using an ion exchange separation of As(III)/As(V) on a continuous FIA-IE-HG-AAS system. The total arsenic concentration was determined together with total concentration of the main alkaline or alkaline-earth metals and anions in the natural waters. Temperature compensated measurements of the pH and redox potentials were made in-situ at the sampling sites.For both seasonal campaigns, the agreement between predicted and experimental As(III) is really high for those samples belonging to non polluted river waters.     

Asymmetric hetero Diels-Alder as an access to carbacephams.

A short and efficient asymmetric synthesis of the (6R,7S)-7-tert-butoxycarbonylamino-2-ketocarbacepham is described. The key step involves the hetero Diels-Alder reaction of the benzylimine derived from the enantiomer of Garner's aldehyde with Danishefsky's diene.     

Intercalation of Dyes Containing SO3H Groups into Zn–Al Layered Double Hydroxide

The intercalates of Naphthol Yellow S, Tropaeolin 000, and Tropaeolin 00 were prepared by heating [Zn_0.67Al_0.33(OH)₂](CO₃)_0.165 · 0.5H₂O with acidic forms of the dye solutions in an open reaction vessel. The intercalates were characterized by chemical and thermal analysis, X-ray powder diffraction and UV–VIS spectroscopy. A possible arrangement of the dye molecules in the intercalates was suggested on the basis of their chemical compositions and interlayer distances, by taking into account van der Waals dimensions of the guest molecules and by assuming that the structure of the host layers is not changed during the intercalation process.     

Changes in the physicochemical properties of transferrin upon chemical derivatization with ceramides

The interaction of native and derivatized transferrin with lecithin, cholesterol and their mixtures was studied using monomolecular layers of phospholipids. Moreover, the thermodynamic parameters corresponding to these interactions: the mixing excess free energy, interaction energy, and interaction parameter were also calculated.The ability of these two proteins to insert into monolayers was studied working at constant area.The formation of aggregates or secondary structures in solution was determined by the fluorescence and polarization values of ANS (anilinonaphthalene sulfonate), measured at different protein/ANS relationships.Abbreviations TF Transferrin - DTF derivatized transferrin - PC lecithin - CHOL cholesterol - CER ceramides - ANS anilinonaphthalene sulfonate - TNBS trinitro benzenesulfonate method