Fluordiazadiphosphetidine, 3. Mitt.: Die thermische Behandlung von 2,2,2,4,4,4-Hexafluoro-1,3-dimethyl-1,3,2,4-diazadiphosphetidin unter Druck in Gegenwart von Phosphor(V)fluorid und Alkalimetallfluoriden

Prolonged heating of (CH₃NPF₃)₂ in a sealed tube at 120°C yields (CH₃N)₄P₃F₇ and PF₅. Under the experimental conditions these compounds react to (CH₃N)₄P₃F₆ ⁺PF₆ ^–. Reaction of (CH₃NPF₃)₂ in the presence of PF₅ leads to a marked decrease in the formation of the ionic compound. The influence of the fluoride donating saltsMF (M=Li, Na, K, Cs) is investigated.

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Früher: Alkyliminophosphorsäuretrihalogenide, 1. und 2. Mitt.     

Fake molecular-orbital calculations

The FAKE method of approximate molecular-orbital calculations is presented and illustrated by application to a number of molecules. The method is of the extended Huckel type but uses accurately computed kinetic-energy matrix elements and avoids scale factors of the Wolfsberg—Helmholtz type. It also includes neighbor-atom charge effects and single-center off-diagonal matrix elements. These features permit FAKE occupied-orbital energies and charge distributions to come into close agreement with corresponding ab initio quantities.     

An inequality relating the regulator and the discriminant of a number field

Let K be a number field of degree d with regulator R_K and absolute discriminant D_K. Let r(K) be the rank of the unit group in K, and let p(K) be the maximum of r(k) as k ranges over proper subfields of K. We prove

$\text{R}{}_{\mathrm{K}}\text{> c}{}_{\mathrm{d}}\text{(}\text{log}\text{γ}{}_{\mathrm{d}}\text{D}{}_{\mathrm{K}}\text{)}{}^{\mathrm{r(K)?\rho (K)}}$

for constants c_d, γ_d > 0 depending only on d.     

Synthesis of some 6-methoxyimidazo[1,2-b]pyridazines

The synthesis of 6-methoxyimidazo[1,2-b]pyridazine and its 2-methyl analog is reported. Carboxylic acids, esters and quaternary salts derived from this ring system are described and the heterocyclic system is shown to undergo the Mannich reaction. A condensation reaction of the 2-methyl group is reported and nuclear magnetic resonance (nmr) spectra and acidity constants of some imidazo[1,2-b]pyridazines are recorded.     

The molecular structure of norbornene as determined by electron diffraction and microwave spectroscopy

The molecular structure of norbornene has been investigated in the gas phase by combining electron diffraction data with microwave spectroscopic rotational constants. The interatomic distances (r_g) and bond angles were obtained by applying a least squares program to the refined experimental molecular diffraction intensities. The CC bond length was found to be 1.336 ± 0.002 Å while the

) bond length was 1. 529 ± 0.007 Å. Other bond lengths and angles included (IUPAC numbering system was used for norbornene): C₁-C₆ = 1.550 ± 0.020 Å, C₁-C₇ = 1.566± 0.005 Å, C₅-C₆ = 1.556 ± 0.005 Å, C-H_ave. = 1.103 ± 0.003 Å, ∠C₁C₂C₄ = 95.3°. The dihedral angle between planes C₁C₂C₃C₄ and C₁C₆C₅C₄ is 110.8 ± 1.5° while that between C₁C₂C₃C₄ and C₁C₇C₄ is 122.3°. The moments of inertia calculated from ED structure are in good agreement with microwave spectroscopic values.     

Multiply doped nanostructured silicate sol-gel thin films: spatial segregation of dopants, energy transfer, and distance measurements

Physical and chemical strategies that place designed molecules in spatially separated regions of surfactant-templated mesostructured silicate thin films are used to prepare films containing rhodamine 6G (R6G), lanthanide complexes, and both simultaneously. Fluorescence and photoexcitation spectra of R6G in amorphous and structured thin films show that it is located inside the surfactant micelles of structured thin films. A silylated ligand that binds lanthanides condenses to form part of the silica framework and causes the lanthanide to localize in the silica. Luminescence and photoexcitation spectra show that energy transfer from the metal complex to R6G occurs in the films. R6G quenches Tb emission in a concentration-dependent manner. Energy transfer efficiency is calculated using the Tb luminescence lifetime, and this quantity is used to calculate the distance between Tb and R6G with the aid of Forster theory.     

Dielectric properties of beryllia ceramics in the near-millimeter wavelength range

We report the refractive indices and absorption coefficients for four beryllia (BeO) ceramic samples. These dielectric properties have been measured over the range from 4 to 18 cm^–1 by use of a Michelson interferometer. The index n, follows the linear relationship n=0.6517 cm³/g×+0.7130 with density, , over the range 2.8<<3.0 g/cm³.     

Stereochemical investigations of a novel class of chiral phosphapalladacycle complexes derived from 1-[(2,5-dimethyl)phenyl]ethyldiphenylphosphine

The phosphapalladacycle derived from 1-(2',5'-dimethylphenyl)ethyldiphenylphosphine has been prepared in the optically active and racemic forms. The phosphine was synthesized as a racemate by the treatment of 1-chloro-1-(2',5'-dimethylphenyl)ethane with sodium diphenylphosphide in THF. The racemic phosphapalladacycle was subsequently obtained as the chloro-bridged dimer by the treatment of the phosphine with palladium(II) acetate followed by anion metathesis with lithium chloride. Alternatively, the phosphine could be optically resolved via metal complexation using (R,R)-bis(mu-chloro)bis{1-[1-(N,N-dimethylamino)ethyl]naphthyl-C(2),N}dipalladium(II) as the resolving agent. An efficient separation of the resulting diastereomeric complexes was achieved by silica gel chromatography. The obtained optically resolved diastereomers were next subject to chemoselective removal of the (R)-N,N-(dimethylamino)-1-(1-naphthyl)ethylaminate auxiliary by treatment with concentrated hydrochloric acid. This process yielded the binuclear dimer complexes containing the resolved eta(1)-P ligand. Cyclopalladation of the coordinated phosphine could next be performed by treatment of its eta(1)-P binuclear dimer with silver(I) hexafluorophosphate(V) in a dichloromethane/water mixture followed by treatment with lithium chloride, giving rise to a pair of optically pure enantiomeric dimers with [alpha](D) -322 and +319 degrees in CH(2)Cl(2). Despite the possibilities of the phosphine to attain a five- membered structure by ortho-palladation or a six-membered ring formation by aliphatic C-H bond activation, only the former was observed. X-ray crystallographic data of the meso dimer and an acetylacetonate derivative indicated that the phosphapalladacycle alpha-C methyl substituent was axially located. The 2-D (1)H-(1)H ROESY spectrum of the acetylacetonate derivative further revealed that the phosphapalladacycle was conformationally rigid in CDCl(3).     

Quantitative TOF-SIMS analysis of oligomeric degradation products at the surface of biodegradable poly(alpha-hydroxy acid)s

This paper reports the development of a new method for quantification of the hydrolytic surface degradation kinetics of biodegradable poly(alpha-hydroxy acid)s using time-of-flight secondary ion mass spectrometry (TOF-SIMS). We report results from static SIMS spectra of a series of poly(alpha-hydroxy acid)s including poly(glycolic acid), poly(L-lactic acid), and random poly(D,L-lactic acid-co-glycolic acid) hydrolyzed in various buffer systems. The distribution of the most intense peak intensities of ions generated in high mass range of the spectrum reflects the intact degradation products (oligomeric hydrolysis products) of each biodegradable polymer. First, a detailed analysis of the oligomeric ions is given based on rearrangement of the intact hydrolysis products. The pattern of ions can distinguish both degradation-generated intact oligomers and their fragment ion peaks with a variety of combinations of each repeat unit. Then, the integration and summation of the area of all ion peaks with the same number of repeat units is proposed as a measurement that provides a more accurate MW average than the typically used method which counts only the most intense peak. The multiple ion summation method described in this paper would be practical in the improvement of quantitative TOF-SIMS studies as a better data reduction method, especially in the surface degradation kinetics of biodegradable polymers.     

Synthesis and optical properties of unsymmetrical conjugated dendrimers focally anchored with perylenes in different geometries

Two sets of light-harvesting monodendrons with unsymmetrical conjugated phenylacetylene branches and perylene cores, one with pi-conjugation from the branches to the core and one without, were synthesized and their photophysical properties were studied by steady-state and time-resolved spectroscopic methods. These monodendrons show comparably high fluorescence quantum yields and efficient energy-transfer properties.