Thermogravimetrische Untersuchung der reduzierenden Chlorierung von Tonerde

Thermogravimetric analysis of the reducing chlorination of alumina The kinetics of the chlorination of dehydrated alumina with (CO/Cl₂) mixtures were studied in the temperature range of 400–900°. The temperature of dehydration of the alumina was shown to be critical for the reaction rates of the subsequent chlorination. Optimal reaction rates could be observed with equimolar (CO/Cl₂) mixtures in the range of 600–700°. At higher temperatures, only a very small increase in reaction rates with increasing temperature could be observed which is thought to be due to the influence of gaseous diffusion gradients in the porous alumina and a progressive decrease in surface area. Granulometric as well as scanning electron microscope studies have shown that with progressing reaction the alumina particles become hollow while retaining their outer shape and size up to a high degree of conversion.     

Multimetallic ruthenium(II) complexes as electrochemiluminescent labels

Two homometallic complexes containing two and three ruthenium polypyridyl units linked by amino acid lysine (Lys) and the related dipeptide (LysLys) were synthesized and their electrochemical, spectroscopic, and electrochemiluminescence (ECL) properties were investigated. The electrochemical and photophysical data indicate that the two metal complexes largely retain the electronic properties of the reference compound for the separate ruthenium moieties in the two bridged complexes, [4-carboxypropyl-4'-methyl-2,2'-bipyridine]bis(2,2'-bipyridine)ruthenium(II) complex. The ECL studies, performed in aqueous media in the presence of tri-n-propylamine as co-reactant, show that the ECL intensity increases by 30% for the dinuclear and trinuclear complexes compared to the reference. Heterogeneous ECL immunoassay studies, performed on larger dendritic complexes containing up to eight ruthenium units, demonstrate that limitations due to the slow diffusion can easily be overcome by means of nanoparticle technology. In this case, the ECL signal is proportional to the number of ruthenium units. Multimetallic systems with several ruthenium centers may, however, undergo nonspecific bonding to streptavidin-coated particles or to antibodies, thereby increasing the background ECL intensity and lowering the sensitivity of the immunoassay.     

Synthese und reaktionsverhalten asymmetrischer metallacyclen des palladiums und platins

The preparation, properties and the complexation behaviour of o-lithiobenzyldiorganoarsines are described. Halogen-bridged binuclear complexes of the type [μ-Cl$\text{M(}\text{o}\text{-C}{}_6\text{C}{}_4\text{CH}{}_2\text{E}$R₂)]₂ (M = Pd, Pt; E = N,P) react with o-LiC₆H₄CH₂ER₂ (E = N, P, As), to form asymmetric metallacycles with two different donor atoms in the molecule. Some physical and chemical properties of these interesting complexes are discussed.     

C-Glucuronides,a Novel Type of Drug Metabolites

The structure elucidation of C-β-glucuronides of sulfinpyrazone (Anturan^®) and phenylbutazone (Butazolidin^®) by spectroscopic means is reported. These conjugates represent a novel type of drug metabolites.     

Novel High-Performance Ceramics—Amorphous Inorganic Networks from Molecular Precursors

Materials research is an interdisciplinary field in which engineers and physical scientists work together. Since the major binary oxides, nitrides, and carbides, which are currently used as high-performance ceramics, were discovered in the last century, the role of chemistry in the development of materials has become barely noticeable. This has changed only in the recent past as, for example, purity and defined morphology of starting powders were recognized as crucial parameters for enhancing the reliability of ceramic workpieces. While the application of chemical methods led to gradual–though significant–improvements, the true potential of chemistry lies rather in the exploitation of new chemical systems and the development of new preparative routes to already known materials. Such an approach is the preparation of ceramics from molecular or polymeric precursors. Herein we survey the most important contributions to those preparative routes starting from the pioneering work in the 1960s and the 1970s; a certain emphasis is placed on the concepts that we have applied to the preparation of multinary, nonoxide materials and amorphous inorganic networks. The name “amorphous high-performance ceramics” is in fact a contradiction in terms. Such materials are thermodynamically unstable with respect to the transformation or decomposition to crystalline phases, thus excluding their application in sensitive areas at high temperatures. However, the selection of element combinations for which the binding energies are derived from strong, local covalent bonds and which are therefore less dependent on a long-range crystalline order, can yield amorphous materials of remarkable thermal and mechanical durability. This is exemplified by novel quaternary ceramics in the Si/B/N/C system, for which an efficient synthesis, starting from raw materials suitable for industrial production, has been developed. For instance, a material of the composition SiBN₃C remains amorphous up to 1900°C, which is unique, and, with respect to oxidation, is the most stable nonoxide ceramic known to date. Another advantage of this in several respects unsurpassed material is the simple way, in which the viscosity of the polymeric precursors can be adjusted to various methods of shaping. So far infiltrations and coatings have been realized. Most developed is the preparation of fibers, which in terms of their performance characteristics are significantly better than those currently available.     

Das erste Oxogallat mit Tetraeder-Ketten [1]

The First Oxogallate with Chains of Tetrahedra For the first time K₂Na₄[(GaO₃)₂] was obtained by annealing intimate mixtures of the binary oxides (K:Na:Ga = 4.4:2.2:1, Ag-cylinder, 600°C, 25 d). The structure elucidation (four-circle diffractometer, MoKα, 506 of 650 I_o(hkl); R = 8.16%, R_w = 4.43%) confirms the space group Pnma with a = 651.5(1), b = 613.2(1), c = 1024.5(1) pm, Z = 2 (Guinier-Simon-photographs). Essential part of the structure is the ?Zweier-Einfach-Kette”? [(GaO(1)_1/1 O(3)_1/1O(2)_2/2)₂]. Despite different space groups the structural similarity with Rb₂Na₄[(FeO₃)₂] is obvious.