The aggregation behaviour of aqueous solutions of the azo dye Acid Red 266 has been investigated by a combination of three di †erent analytical methods : 19F NMR, UV/Vis spectroscopy, and static light scattering (SLS). For a better comparison the same range of concentration was studied by all three methods. The NMR data were interpreted in terms of a monomer/dimer equilibrium and, additionally, of a monomer/n-merequilibrium, based on an isodesmic model. No distinction between both equilibria was possible. Modelling the UV/Vis data by a monomer/dimer equilibrium gives access to all of the important thermodynamic quantities associated with a dimerization. The major driving force for aggregation is enthalpic with *H D \ [22.10 kJ mol~1, whereas a positive entropy of 7 J mol~1 K~1 points to a solvent contribution. The value of ^0.50 the free dimerization enthalpy is in good agreement with that from NMR results. Furthermore, the UV/Vis data revealed information on the local arrangement of the nearest neighbours in the dyestu † aggregates. The constituting molecules are separated by an interplanar distance of 0.69 nm and are twisted against each other by an angle of 50¡ (calculated from exciton theory). This twist angle proves that the group of one Acid CF 3 Red 266 molecule must be covered by an adjacent benzene ring within the aggregate and supports the conclusion obtained from NMR measurements. Both spectroscopic methods indicate a vertical stacking of the dye molecules, conÐrming a columnar structure of the aggregates. In contrast, SLS indicates the existence of highly aggregated species in dilute solutions of 10~6È10~4 mol L~1 with molecular weights and contour lengths in the order of magnitude of 105È106, and up to 700 nm, respectively. In addition to aggregation numbers, the overall shape of the aggregates were supplemented by SLS, suggesting a worm-like structure. Both, the contour lengths and the cross sections of the aggregates can be modiÐed by addition of electrolyte, resulting in an increase of chain sti †ness. Finally, the apparent discrepancies between the results of the spectroscopic methods and of SLS are discussed.
Darstellung, Eigenschaften und IR‐Spektren von L2Pd(N3)2 (L = Phosphin, Amin), [(C6H5)3P]2MN3 (M = CuI, AgI), (C6H5)3PAuN3, [(C6H5))3P]3MN3 (M = AuI, RhI), [(C6H5)3P]4Rh2(N3)2 und [(C6H5)3P]2Ir(CO)N3 werden beschrieben. Die Palladium‐, Gold‐, Rhodium‐ und Iridiumverbindungen reagieren in Chloroform‐ oder Benzollösung mit Kohlenmonoxid unter Bildung der entsprechenden Isocyanato‐Komplexe. Auch die dimere Verbindung [(C6H5)3PPd(N3)2]2 bildet mit CO einen Komplex [(C6H5)3PPd(NCO)2]2, der vermutlich Isocyanat‐Brücken enthält. Der Mechanismus dieser Reaktionen wird aufgrund orientierender kinetischer Untersuchungen diskutiert.
Oxidation of Bi2Te3 (space group R-3m) has been investigated using experimental and theoretical means. Based on calorimetry, x-ray photoelectron spectroscopy and thermodynamic modelling, Bi2Te3 is at equilibrium with Bi2O3 and TeO2, whereby the most stable compound is Bi2Te3, followed by Bi2O3. Hence, the reactivity of Bi towards oxygen is expected to be higher than that of Te. This notion is supported by density functional theory. The strongest bond is formed between Bi and Te, followed by Bi - O. This gives rise to unanticipated atomic processes. Dissociatively adsorbed oxygen diffuses through Bi and Te basal planes of Bi2Te3(0001) and preferably interacts with Bi. The Te termination considerably retards this process. These findings may clarify conflicting literature data. Any basal plane off-cut or Bi terminations trigger oxidation, but a perfect basal cleavage, where only Te terminations are exposed to air, may be stable for a longer period of time. These results are of relevance for applications in which surfaces are of key importance, such as nanostructured Bi2Te3 thermoelectric devices.
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