Determination of pit-coal ash content with the use of an (α, n) neutron source

Activation with fast neutrons from a Pu/Be source enables the ²⁸Si(n, p)²⁸ Al and ²⁷Al(n p)²⁷Mg reactions to be utilized. Seventy-two samples of pit coals with ash contents ranging from 3 to 40% were measured. The calibration function between ash content and both 1.78- and 0.84-MeV γ-ray counts was linear. The standard deviation was 0.9% for a 17% ash content and 1.4% over the whole range of ash contents. Comparison with other methods is discussed.     

Going beyond the borders: pyrrolo[3,2-b]pyrroles with deep red emission

A two-step route to strongly absorbing and efficiently orange to deep red fluorescent, doubly B/N-doped, ladder-type pyrrolo[3,2-b]pyrroles has been developed. We synthesize and study a series of derivatives of these four-coordinate boron-containing, nominally quadrupolar materials, which mostly exhibit one-photon absorption in the 500–600 nm range with the peak molar extinction coefficients reaching 150 000, and emission in the 520–670 nm range with the fluorescence quantum yields reaching 0.90. Within the family of these ultrastable dyes even small structural changes lead to significant variations of the photophysical properties, in some cases attributed to reversal of energy ordering of alternate-parity excited electronic states. Effective preservation of ground-state inversion symmetry was evidenced by very weak two-photon absorption (2PA) at excitation wavelengths corresponding to the lowest-energy, strongly one-photon allowed purely electronic transition. π-Expanded derivatives and those possessing electron-donating groups showed the most red-shifted absorption- and emission spectra, while displaying remarkably high peak 2PA cross-section (σ_2PA) values reaching ∼2400 GM at around 760 nm, corresponding to a two-photon allowed higher-energy excited state. At the same time, derivatives lacking π-expansion were found to have a relatively weak 2PA peak centered at ca. 800–900 nm with the maximum σ_2PA ∼50–250 GM. Our findings are augmented by theoretical calculations performed using TD-DFT method, which reproduce the main experimental trends, including the 2PA, in a nearly quantitative manner. Electrochemical studies revealed that the HOMO of the new dyes is located at ca. −5.35 eV making them relatively electron rich in spite of the presence of two B⁻–N⁺ dative bonds. These dyes undergo a fully reversible first oxidation, located on the diphenylpyrrolo[3,2-b]pyrrole core, directly to the di(radical cation) stage.

Ladder-type heterocycles encompassing two B⁻–N⁺ dative bonds possess intense green to red emission, large 2PA cross-sections and superb photostability.     

Abrupt Spin-State Switching in Mn(III) Complexes with BPh4 Anion: Effect of Halide Substituents on Crystal Structure and Magnetic Properties.

Three tetraphenylborates of mononuclear Mn(III) cation complexes with hexadentate ligands, the products of the reaction between a N,N′-bis(3-aminopropyl)ethylenediamine and salicylaldehydes with the different haloid substitutions at the 5 or 3,5 positions, have been synthesized: [Mn(5-F-sal-N-1,5,8,12)]BPh₄ ( 1 ), [Mn(3,5-diCl-sal-N-1,5,8,12)]BPh₄ ( 2 ) and [Mn(3,5-Br,Cl-sal-N-1,5,8,12)]BPh₄ ( 3 ). Their crystal structure, dielectric constant (ϵ) and magnetic properties have been studied. Ligand substituents have a dramatic effect on the structure and magnetic properties of the complexes. With decreasing temperature, the complex ( 1 ) shows a gradual spin crossover from the high-spin state (HS) to the HS:LS intermediate phase, followed by an abrupt transition to the low-spin state (LS) without changing the crystal symmetry. The complexes 2 and 3 are isostructural, but have fundamentally different properties. Complex 2 demonstrates two structural phase transitions related to sharp spin crossovers from the HS to the HS:LS intermediate phase at 137 K and from the intermediate phase to the LS at 87 K, while complex 3 exhibits only one spin transition from the HS to the HS:LS intermediate phase at 83 K.     

The reaction of direct phenylation by nucleogenic cations as a method of synthesis of unknown or complicated tritium labeled compounds

As a result of ion-molecular reactions of nucleogenic phenyl cations, generated by tritium β-decay in polytritiated benzene, with nucleophilic centers of investigated substrates the direct phenylation has been realized at first time and unknown tritium labeled aromatic derivatives of polyvalent fluorine together with the different N-phenyl substituted pyridinium compounds which are important syntones for biological and medical investigations have been synthesized.     

Luminescent salt

In this contribution, we report on the f-f and d-f luminescence of Ce³⁺, Pr³⁺ and Nd³⁺ in NaCl. The samples were prepared by rapid quenching of a NaCl-melt doped with lanthanides. It is shown that both f-f and d-f emission from lanthanide ions can be observed. Excitation and emission spectra are discussed. In addition to being interesting from a fundamental point of view, it will be argued how the simple alkali halides doped with trivalent lanthanides may be promising as hosts for new scintillator materials.     

Magnetic properties of polymer matrix nanocomposites on a basis of metal carboxylates

Metallopolymer nanocomposites on the bases of cobalt and iron acrylates as well as their cocrystallites have been obtained and characterized. Microstructure of the materials consists of both agglomerated and individual nanocrystallites which are homogeneously distributed in the polymer matrix. Mean crystallite size is 7-14 nm. All the composite materials exhibit soft magnetic properties at room temperature. The magnetic parameters are controlled by the intrinsic magnetic properties of the constituents and agglomeration of the particles.     

The effect of photostabilizers on polymeric insulation used at high voltages

Polymeric insulation used in high voltage applications and subjected to divergent electric fields emits ultraviolet radiation due to electroluminescence. The chromophores present in the polymer initiate photo-degradation of the material and, in dry environment, this leads to electrical treeing which causes premature failure of the insulation. The role of photostabilizers which can limit the photodegradation caused by ultraviolet radiation is studied for LDPE containing the usual and decreased concentration of air. Degassing or impregnating the polymer with an inert gas decreases the concentration of oxygen and prolongs the time to tree inception because the probability of forming excited or anionic oxygen is reduced.     

Phosphorylated imidazo[1,2-a]pyridines

The reaction of phosphorus(III) halides with imidazo[1,2-a]pyridines in the presence of bases leads to the formation of 3-phosphorylated imidazo[1,2-a]pyridines. The reaction proceeds in high yield and requires no catalysts. In the compounds obtained, in contrast to phosphorylated indolizines, the phosphorus–heterocycle bond is stable and not cleaved by dry hydrogen chloride, alcohols, or water. Imidazo[1,2-a]pyridines with the phosphinic and phosphinous groups can be alkylated both at the phosphorus and at the nitrogen atom of the heterocycle, the alkylation direction being dependent on the strength of the alkylation reagent used. © 1995 John Wiley & Sons, Inc.