Einfluß der Anionensolvatation auf die Komplexbildung in Donorlösungsmitteln

Zusammenfassung Der Einfluß der Anionensolvatation auf die Komplexbildung in Donorlösungsmitteln wird folgendermaßen beschrieben: Der thermodynamische Solvatationseffekt hängt vom Verhältnis der freien Solvatationsenthalpien zur freien Enthalpie des Gesamtvorganges der Komplexbildung ab; d. h., je geringer die Akzeptorstärke des Akzeptors, um so mehr wird durch die Solvatation die Donorstärke eines Anions im Vergleich zu derjenigen des Neutraldonors erniedrigt. Der spezifische Solvatationseffekt bringt das spezifische Solvatisierungsvermögen eines Lösungsmittels gegenüber einem Anion (bei gegebenem Akzeptor) zum Ausdruck. Protonenhaltige Lösungsmittel, z. B. Wasser, Methanol, Essigsäure, Ameisensäure, Formamid, haben eine hohe Tendenz zur Wasserstoffbrückenwechselwirkung; sie solvatisieren Halogenid- und Pseudohalogenidionen wesentlich stärker als aprotische Donorlösungsmittel. Die Donorstärke eines anionischen Liganden wird in einem solchen Lösungsmittel entsprechend erniedrigt. Zum Vergleich der Stabilität eines Komplexes in verschiedenen Lösungsmitteln können ihre Donizitäten allein nicht herangezogen werden. Die solvatisierenden Eigenschaften von Donorlösungsmitteln nehmen ab: H₂O>ROHDMSOES>ANTMSNMDMF>DMA>HMPT.

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The influence of anion-solvation on complex formation in donor solvents

The said influence is described as follows: the thermodynamic solvation effect depends on the ratio of the free enthalpy of solvation to the free enthalpy of the complex forming reaction. It is increased by decreasing acceptor strength of the acceptor. The specific solvation effect is due to the specific solvating power of a solvent towards an anion (with given acceptor). Protonic solvents are known to have higher tendencies for hydrogen bridge interactions. They are stronger solvating agents for halide and pseudohalide ions than aprotic donor solvents. The donor properties of a donor anion is decreased in such solvents and the donicity alone is no longer a useful guide to estimate the relative stabilities of a complex in such media. The solvating properties of donor solvents decrease in the following order: H₂O>ROHDMSOES>ANTMSNMDMF>DMA>HMPT.

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Herrn Professor Dr.Richard Kieffer zum 65. Geburtstag gewidmet.     

Study of the oxygen distribution in YBa2Cu3O7−x ceramics by (n, α) radiography technique

A technique to determine the oxygen distribution in high T_c superconducting YBa₂Cu₃O_7–x ceramics has been developed which is based on the (n, ) radiography method. The technique enables the non-destructive study of superconducting ceramics as well as monocrystal samples with spatial resolution not worse than 1 m at a relative standard deviation of 1.5%. This technique is used to study the influence of radiation-stimulated diffussion of oxygen on the formation of the superconducting phase in an yttrium ceramic. The oxygen distribution in the samples with a narrow transition (T1 K) and with a transition widened (T10 K) by thermal and thermo-radiative treatment is compared in the experiment. The oxygen distribution radiographs of irradiated and unirradiated samples provide strong evidence for the influence of irradiation on the ordering of superconducting ceramics structure.     

Separation of Cs and Sr using polyoxonium compounds

Extraction separation and concentration of Cs and Sr from aqueous solutions, containing macroconcentrations of competitive ions (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Al³⁺, Fe³⁺) by the nitrobenzene solutions of bis-1,2-dicarbollylcobaltate in the presence of linear and cyclic polyoxonium compounds (POC) has been investigated. It has been found, that the addition of DB18C6 increases the distribution ratio of cesium (D_cs) but the addition of other crowns and PEG decreases D_Cs value and selectivity of D_Sr and the selectivity of Sr/Ca separation. Separation factors of Sr/Ca increase from (Sr/Ca)2 (found in the absence of POD) to (Sr/Ca)50 (for DB18C6), (Sr/Ca)100 (for 18C6 and DCH18C6) and (Sr/Ca)1000 for 15C5.     

Spectrophotometric Determination of the Polyiodohalides of Organic Nitrogen-Containing Cations

The following biologically active diiodohalides of organic cations were studied: N-cetylpyridinium, trimethylbenzylammonium, triethylbenzylammonium, and N,N-dimethylmorpholinium diiodochlorides; N-cetylpyridinium, tetramethylammonium, tetrabutylammonium, and N,N-dimethylmorpholinium diiodobromides; and N,N-dimethylmorpholinium and butyroylcholinium triiodides. A simple and rapid procedure was proposed for the determination of the above compounds; it is based on the conversion of organic diiodohalides into the corresponding triiodides (_{300 nm} 4 × 10⁴; _{370 nm} 2 × 10⁴) in the presence of excess potassium iodide (RSD 2%). An extraction–spectrophotometric method was developed for the quantitative determination of the biologically active compounds in pharmaceutical dosage forms based on their ion associates with anionic dyes, erythrosine (m _min = 1.25–3.30 g; RSD 3%) and Bromothymol Blue (m _min = 3.85 g; RSD = 3%), or a cationic dye—1,3-dimethyl-2-(4-morpholinophenyl)azobenzimidazolium phenylsulfate (m _min = 2.32–8.26 g; RSD 4%). The developed procedures were used for monitoring drug substances in model pharmaceutical preparations (RSD 4%).     

Free Radicals in the Photolysis and Radiolysis of Polymers: IV. Radicals in γ- and UV-Irradiated Wood and Lignin

Free radicals formed in the radiolysis and photolysis of wood and lignin were studied using X-band and D-band EPR measurements. It was found that singlet spectra at g 2, which appeared upon the low-temperature (77 K) - and UV irradiation of wood and lignin, or singlets detected in a posteffect on heating the irradiated samples belong to radicals having conjugated carbon–carbon bonds. Formyl radicals in -irradiated wood and peroxide radicals in - and UV-irradiated wood were detected for the first time using EPR spectra. The radiation-chemical and quantum yields of radical formation reactions were determined. In wood at 77 K, G _R 3.2 1/100 eV and _R 2 × 10^–3.     

Conformation analysis of diphosphine

Extended basis set ab initio computations are performed on HF, PNO-CI and CEPA level to determine the structure of P₂H₄ and the potential curve E() for rotation around the P-P axis. The structure parameters are optimized for dihedral angles of 0 ° (cis), 50 °, 80 ° (gauche or semi-eclipsed), 130 °, and 180 ° (trans). It turns out that P₂H₄ has a gauche equilibrium structure, a local minimum for trans which is 2.5 kJ/mol above gauche, a rather large cis barrier of 20 kJ/mol and a gauche trans barrier of 3.5 kJ/mol. The potential E() is extremely flat in the region 50 ° < < 310 °, where E() varies by less than 5 kJ/mol. Electron correlation tends to reduce the barriers but has no drastic effect on E().     

Aqueous solubilities and octanol-water partition coefficients of binary liquid mixtures of organic compounds at 25°C

From thermodynamics and certain assumptions it is shown that, under the usual experimental conditions, the octanol-water partition coefficient (K_o/w) of a given organic liquid should be the same whether the substance is partitioned neat or as part of a mixture. Measurements of several mixtures of n-propylbenzene (log K_o/w=3.71±0.04)+ethylbenzene (log K_o/w=3.16±0.01) clearly confirm this. It is also shown that the aqueous solubility (S_w) of a neat organic liquid can be related to its aqueous solubility (S _w ), when it is present at volume fraction in an organic liquid mixture, by S _w =S_w, where is its activity coefficient in the organic mixture. The measured S _w values for n-propylbenzene + ethylbenzene (1), n-hexane + nitrobenzene (>1) and di-isopropyl ether + chloroform (<1) are found to be in good agreement with the predicted values (average differences of, respectively, <2%, 8% and 6%). In general, the bounds on S _w are expected to be 0w w.     

TEM investigation of TiNx-PACVD-coatings

The wear resistance of cermet cutting tools can be remarkably increased by TiN_x coatings. These layers are deposited at substrate temperatures of 723 K, 773 K and 973 K using a plasma-assisted chemical vapour deposition (PACVD) process. TEM investigations combined with EDXS analysis and electron diffraction gave information on structure and composition of the TiN_x layers and the interface range. X-ray structure investigations were performed additionally.The structure and the chlorine content of layers and interfaces change in dependence on the deposition temperature. All coatings show a columnar structure, but the fibre diameter increases with temperature. The fine-grained TiN_x layer deposited at 723 K has the highest chlorine content, a low-developed columnar structure and a 111 texture. The coatings deposited at 773 K and 973 K contain less chlorine impurities and have a 100 preferred orientation. The fibre structures at 723 K and 773 K can be resolved into single crystallites. By TEM investigations the fibres formed at 773 K are proved to be an accumulation of neighbouring and similarly oriented crystallites. Grain size determined by X-ray analysis and fibre diameter agree with each other. Grain sizes determined more exactly from TEM images are 6 nm at 723 K, 10 nm at 773 K and 30 nm at 973 K. In the interface region the thickness and the chlorine content of this zone decreases with increasing deposition temperature and simultaneously the layer adhesion increases.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Lithium intercalation in layer structured compound β-ZrNCl

A layer structured crystal -ZrNCl forms a lithium intercalation compound Li_xZrNCl. The upper limit for x determined on the compound prepared by the n-butyl lithium technique is 0.29. In the electrochemical process, a pressed -ZrNCl cathode is further reduced up to x=11.25 at potentials as low as 0.80.6 V relative to Li/Li⁺. The lithium intercalate swells in various polar solvents, increasing the basal spacing. However, in contrast to the salt-like intercalates of transition metal chalcogenides and FeOCl, the lithium intercalated -ZrNCl does not form hydration phases, but reacts with water, evolving hydrogen. These results can be interpreted in terms of the formation of an alloy-like intercalate like the alkali intercalates of graphite. On intercalation, -ZrNCl is changed from pale yellow-green to black in color, and the electrical conductivity increases by a factor of 10⁶.     

Laser Sintering of SnO2 : Sb Sol-Gel Coatings

Sb doped sol-gel SnO2 single layers (thickness 100 nm) were prepared from alcoholic solution and deposited via a dip coating process on fused silica substrates. The coatings have been sintered at a typical rate of 10–15 cm2/s by CO2 laser irradiation. The laser spot was scanned in one direction at a speed of 15,000 cm/s and the sample was moved in a perpendicular one at a speed up to 250 mm/s. The temperature of the topmost 10 m layer was monitored by a fast pyrometer (s resolution). The following properties of the coatings have been determined: the electrical resistivity , the carrier density n, and mobility , the structure, the thickness, the mesoscopic and micromorphology and the density. The sintering by CO2 laser radiation is mainly a thermal driven process. At T 500°C it allows to obtain coatings with a smaller resistivity (6.8×10–3 cm) than those produced by conventional furnace firing (el2.9×10–2 cm). The results are discussed in terms of particle size and packing density.