The thermoelectric powers of transition metals at high temperature

This paper is concerned with a survey of the experimental data for the thermoelectric power? The thermoelectric power is hereinafter referred to as TEP of transition metals and with their discussion. For the first time a critical review of the main data, which are given in the literature and proved to be rather incomplete, is presented. When necessary, the author has conducted the TEP measurements within the temperature range of 80° to 1800°k, wherever it was possible. For the first time TEP data have been obtained for scandium, osmium and, effectively, for hafnium; erroneous data for thorium and ruthenium have been corrected; the temperature measuring range for many other metals has been substantially extended. Finally, from the data found in the literature and the new results, a fairly complete notion has been formed of the high-temperature behaviour of TEP for all transition metals (except technetium) in the 3d, 4d, and 5d series of the periodic system, as well as for uranium and thorium. Some empirical regularities in the behaviour of TEP have been detected, the main one of which is that the TEP's of transition metals, which belong to a given column of the periodic table and are in a magnetically disordered state, vary with the temperature above 80°k in a similar way. The paper demonstrates that the TEP of transition metals is characterized by a complex, non-linear temperature dependence. Consequently, the value and sign of the TEP at room temperature cannot serve as a sufficient criterion for characterizing the TEP. The general shape (‘type’) of the TEP temperature curve should be used as the above-mentioned criterion.     

Catalytic aerobic oxidation of substituted 8-methylquinolines in Pd(II)-2,6-pyridinedicarboxylic acid systems

The ability of Pd(II) complexes derived from 2,6-pyridinedicarboxylic acids to catalyze homogeneous regioselective aerobic oxidation of 5- and 6-substituted 8-methylquinolines in AcOH-Ac(2)O solution to produce corresponding 8-quinolylmethyl acetates in high yield was demonstrated; corresponding 8-quinoline carboxylic acids are minor reaction products.     

F-projectors and F-covering subgroups of finite groups

Given a nonempty set ω of primes and a nonempty class F of groups, we define the F ^ω - projector and F ^ω -covering subgroup of a finite group and study their properties (existence, invariance under certain homomorphisms, conjugacy, and embedding). We extend the results of Gasch¨utz, Schunck, Erickson, and others.     

The flow in a planar-radial vortex chamber. 1. An experimental study of the velocity field in transient and steady flows

Two methods for determining the flow velocity in a vortex chamber of planar-radial geometry under transient and steady-state conditions are proposed. Local flow velocities throughout the entire volume of the chamber are measured, and the flow is found to be rotational. The effect of accumulation of particles heavier than air in the butt-end boundary layer is revealed. Lavrent'ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 112–121, November–December, 1999.     

Synthesis,Structure, Spectroscopic Studies,and Complexation of Novel Crown Ether Butadienyl Dyes

Butadienyl dyes of the benzothiazole series with various fragments of benzocrown ethers 1a – c were synthesized for the first time. The structures and spectral properties of crown‐containing butadienyl dyes and their complexes with alkali and alkaline‐earth metal cations were studied by X‐ray diffraction analysis and ¹H‐NMR, UV/VIS, and resonance Raman spectroscopy. To interpret the experimental results, quantum‐chemical calculations were performed. In the case of Sr²⁺ and Ba²⁺ ions, the formation of strong sandwich complexes [M( 1b )₂]²⁺ of an unusual structure involving stacking interactions was established; the dye molecules are arranged one above another in the complex according to the ‘head‐to‐head' pattern.     

N‐Methylbenzoazacrown ethers with the nitrogen atom conjugated with the benzene ring: the improved synthesis and the reasons for the high stability of complexes with metal and ammonium cations

An improved method for the synthesis of formyl derivatives of N‐methylbenzoazacrown ethers is proposed. They are prepared in up to 68% yields over fewer steps and with a much shorter time required for the last step. The stability constants of complexes formed by N‐methylbenzoazacrown ethers and their structural analogs with alkali metal, alkaline‐earth metal and ammonium cations were determined by ¹H NMR titration in CD₃CN. High stability of complexes of N‐methyl derivatives of benzoazacrown ethers is demonstrated, comparable with or even exceeding the stability of benzocrown‐ether complexes and markedly exceeding the stability of complexes of phenylazacrown ethers with the same macrocycle size. The structures of azacrown ethers and their complexes with Ba(ClO₄)₂ were studied by X‐ray diffraction. A high degree of pre‐organization of N‐methylbenzoazacrown ethers toward the formation of complexes with metal and ammonium cations was noted, which is due to the clear‐cut pyramidal geometry of the nitrogen atom and the orientation of the lone electron pairs (LEPs) of most heteroatoms towards the centre of the macroheterocycle. Copyright © 2009 John Wiley & Sons, Ltd.     

Stereospecific [2+2] autophotocycloaddition in the dimeric complex of 18-crown-6 ether styryl dye bearing N-(3-ammoniopropyl) substituent

New 18-crown-6 ether styryl dye of the 4-pyridine series bearing N-(3-ammoniopropyl) substituent has been synthesized. In MeCN, the dye forms a stable dimeric complex of the syn-head-to-tail type due to the complexation of the ammonium group of one molecule with the crown ether fragment of another. In the dimeric complex, the ethylene bonds of the molecules are close in space and antiparallel, which promotes an efficient stereospecific [2+2] autophotocycloaddition to yield the only rctt-isomer of 1,2,3,4-tetrasubstituted cyclobutane. The cyclobutane derivative structure was confirmed by NMR spectroscopy and X-ray diffraction.     

Photophysical properties of aqueous solutions of a styryl dye in the presence of cucurbit[<Emphasis Type="Italic">n</Emphasis>]uril (<Emphasis Type="Italic">n</Emphasis> = 5, 6, 8)

Photophysical properties of aqueous solutions of the styryl dye 4-[(E)-2-(3,4-dimethoxyphenyl)-1-ethylpyridinium] perchlorate (1) in the presence of cucurbit[n]urils (CB[n]; n = 5, 6, 8) have been studied by fluorescent spectroscopy methods. The fluorescence intensity of a 10^–6 mol L^–1 solution of 1 increases by a factor of 12.6 upon the formation of 1 : 1 inclusion complexes with CB[6] or 1.3 in complexes with CB[8]. Upon the formation of inclusion complexes, the average lifetime of the electronically excited state of 1 increases to about 1 ns for both CB[6] and CB[8]. On the basis of fluorescence anisotropy measurements, the rotational relaxation times were estimated to be 408, 314, and 183 ps for the complexes with CB[6], CB[8], and for unbound 1, respectively. Using the fluorescence titration method developed for the case of poorly soluble cavitands, the binding constant of 1 with CB[6] was determined to be 1.1 × 10⁵ L mol^–1. The addition of CB[5] does not lead to changes in the photophysical properties of a solution of 1, indicating the absence of complexes between CB[5] and 1. It has been found on the basis of the experimental data that the fluorescence rate constant of 1 decreases about twice in the complex with CB[8], but doubles in the complex with CB[6].