1,1,3,3,5,5-Hexakis(dimethylamino)-λ5-[1,3,5]triphosphinin – Darstellung,Kristallstruktur und NMR-Daten

1,1,3,3,5,5-Hexakis(dimethylamino)-λ⁵-[1,3,5]triphosphinine – Synthesis, Crystal Structure, and NMR Data Preparation of 1,1,3,3,5,5-hexakis(dimethylamino)-λ⁵-[1,3,5]triphosphinine ( 4 ) and the path of its formation from methyl-bis(dimethylamino)difluorophosphorane ( 1 ) and n-butyllithium are described. The chemical behaviour of compounds of type [R₂P=CH–]_n is compared with that of the isoelectronic dichlorophosphazenes [Cl₂P=N–]_n. The structure of 4 is eludicated by n.m.r. spectra and X-ray structural analysis.     

Synthesis of microsequential methylvinylsiloxane–dimethylsiloxane copolymers by nonequilibrium copolymerization

Nonequilibrium anionic ring-opening copolymerization of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (V₄) with hexamethylcyclotrisiloxane (D₃) was examined as a route to methylvinyl–dimethylsiloxane microsequential copolymers. The copolymerization was carried out in toluene and was initiated with Me₃SiCH₂Li using DMSO as the promoter. Distribution of siloxane units obtained from kinetic analysis based on first-order Markovian statistics was compared with that found from analysis by ²⁹Si NMR spectroscopy. Results showed that although chain transfer and back-biting play some role in this system, the kinetics of copolymerization may be described to a reasonable approximation by the first-order Markov model. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 137–145, 1998     

Identification of amber and imitations by near infrared reflection spectroscopy

Imitations of amber have been prepared since a long time, but the number of imitations is increasing since modern polymers are available. At present, many imitations are based on a few synthetic polymers and even experts have some problems in distinguishing between real and falsed amber without destruction of the material. IR-Spectroscopy or pyrolysis combined with gas chromatography/mass spectrometry are very efficient methods in identifying amber and imitations but these methods need a sample preparation. By means of near infrared reflection spectroscopy it is possible to identify amber and imitations without any sample preparation in a short time. Optimization of the method and the application are discussed.     

Evidence for linkage position determination in cobalt coordinated pentasaccharides using ion trap mass spectrometry

A methodology to determine the linkage position of oligosaccharides is presented. In order to illustrate this technique, several oligosaccharides and disaccharides were ionized by electrospray and analyzed in a Paul trap mass spectrometer. Multiple stage tandem mass spectrometry experiments were used to determine linkage and structural information for the following four cobalt coordinated and singly charged ([M+Co?H]⁺) pentasaccharides: Lacto-N-fucopentaose I, II, III, and V. In order to differentiate between linkage positions, multiple low energy collision induced experiments with mass selected C type ions have been carried out in an ion trap mass spectrometer. Because of the coordination with cobalt, which directs the dissociation pathways, these C type ions undergo specific fragmentation reactions upon low energy collision induced dissociation. These dissociation pathways are unambiguously dependent on their linkage position, thus allowing differentiation between 1→2, 1→3, 1→4, and 1→6 linkage positions throughout the oligomers. Studies on various linked disaccharides and N-acetyl-disaccharides, which are smaller constituents of the pentasaccharides, were used to verify and confirm the results obtained from the pentasaccharides.     

Intercalation materials for lithium rechargeable batteries

An overview is given of intercalation materials for both the negative and the positive electrodes of lithium batteries, including the results of our own research. As well as lithium metal as a negative electrode, we consider insertion materials based on aluminium alloys. In the case of the positive electrode metal-oxides based on manganese, nickel and cobalt are discussed. Received: 27 May 1997 / Accepted: 30 July 1997     

Electrochemical etching of silicon carbide

Both n- and p-type SiC of different doping levels were electrochemically etched by HF. The etch rate (up to 1.5 μm/min) and the surface morphology of p-type 6H-SiC were sensitive to the applied voltage and the HF concentration. The electrochemical valence of 6.3 ± 0.5 elementary charge per SiC molecule was determined. At p-n junctions (p-type layer on a n-type 6H-SiC substrate) a selective etching of the p-type epilayer could be achieved. For a planar 6H-4H polytype junction (n-type, both polytypes with equal doping concentrations) the 4H region was selectively etched under UV illumination. Thus polytype junctions could be marked by electrochemical etching. With HCl instead of HF no etching of SiC occurs, but a SiO₂ layer (thickness up to 8 μm) is formed by anodic oxidation. Received: 29 October 1998 / Accepted: 27 January 1999     

Synthesis and Spectroscopic Studies of Chosen Heteropolytungstates and Their Ln(III) Complexes

The heteropolytungstates [(Na)P₅W₃₀O₁₁₀]^4– (I), [(Na)Sb₉W₂₁O₈₆]^18– (II) and [(Na)As₄W₄₀O₁₄₀]^27– (III) and the monovacant Keggin structure of the general formula [XW_11–xMo_xO₃₉]^n– (X-Si, P; n = 7 for P and 8 for Si) (IV) as well as their europium(III) complexes were studied. The structures of I–IV as well as the europium(III) encrypted [(Eu)P₅W₃₀O₁₁₀]^12– (VI), [(Eu)Sb₉W₂₁O₈₆]^16– (VII), [(Eu)As₄W₄₀O₁₄₀]^25– (VIII) and sandwiched [Eu(XW_11–xMo_xO₃₉)₂]^n– (n =11 for P and n = 13 for Si) (V) complexes were synthesized and spectroscopically characterized. The complexes were studied using UV-Vis absorption and luminescence, as well as the laser-induced europium ion luminescence spectroscopy. Absorption spectra of Nd(III) were used to characterize the complexes formed. Excitation and emission spectra of Eu(III) were obtained for solid complexes and their solutions. The relative luminescence intensities of the Eu(III) ion, expressed as the ratio of the two strongest lines at 594 nm and 615 nm, = I₆₁₅/I₅₉₄, which is sensitive to the environment of the primary coordination sphere about the Eu(III) ion, was calculated. In the case of the sandwiched [Eu(XW_11–xMo_xO₃₉)₂]^n– complexes a linear dependence of the luminescence quantum yield of Eu(III) ion, , (calculated using [Ru(bpy)₃]Cl₂ as a standard) on the content of Mo (number of atoms, x) in the [Eu(XW_11–xMo_xO₃₉)₂]^n– structure was observed.     

Very Large Cyclic Compounds

Very large ring systems, containing more than 50 ring members, are becoming increasingly important in different topics in natural sciences. These so-called gigantocycles differ from smaller macrocycles in physical properties, special structural features and chemical behaviour. This article is meant to be the first summary of such ring systems and a synopsis of the most remarkable examples with their fascinating nano-scaled structures and ingenious synthesis. To restrict the scope of the article, only isolated and completely characterized, monodisperse compounds are presented. Furthermore, attention is mainly directed at organic gigantocycles. Some ultracycles with more than 100 ring members, mainly occurring in polymer chemistry and nature, will also be described.     

The standard enthalpies of formation of some dibenzoannelated cycloalkanols

The heats of combustion of trans-9,10-bis-hydroxymethyl-9,10-dihydrophenanthrene, trans-5-hydroxymethyl-5,6-dihydro-7H-dibenzo[a,c]cyclohepten-6-ol, 5-hydroxymethyl-5,6-dihydro-7H-di-benzo[a,c]cycloheptene, 6-hydroxymethyl-5,6-dihydro-7H-dibenzo[a,c]cycloheptene, 5H-dibenzo-[a,d]cyclohepten-5-ol and 5H-10,11-dihydrodibenzo[a,d]cyclohepten-5-ol were measured by means of a Gallenkamp adiabatic bomb calorimeter. Uncertainties in the determination of the heats of combustion ranged between 0.2 and 0.3%. The enthalpies of formation and atomization for the six compounds were derived. The experimental values of the heats of atomization were compared with those calculated using the Allen–Skinner bond energy scheme. Conclusions about energetic contributions which stabilize the structure of the investigated compounds were drawn.