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941.
Relaxation dynamics of Ag+ ions in several series of AgI-Ag2O-V2O5 superionic glasses has been studied in the frequency range from 10 Hz to 2 MHz and in the temperature range from 93 to 323 K. The composition dependence of the dc conductivity and the activation energy of these glasses has been compared with those of AgI-doped silver phosphate and borate glasses. The frequency-dependent electrical data have been analyzed in the framework of conductivity formalism. We have obtained the mobile ion concentration and the power-law exponent from the analysis of the conductivity spectra. We have observed that the concentration of Ag+ ions is independent of temperature and the conductivity is primarily determined by the mobility. A fraction of the Ag+ ions in the glass compositions are involved in the dynamic process. We have also shown that the power-law exponent is independent of temperature. The results are also supported by the temperature and composition independence of the scaling of the conductivity spectra. 相似文献
942.
We present here a first systematic study of substituent effects in metallocorroles, based on electronic absorption, resonance Raman (RR), and infrared (IR) spectroscopic studies and electrochemical measurements on 10 copper(III) meso-triarylcorroles, Cu(III)[beta-Y(8)TArC], where the beta-substituent Y = H or Br and the meso-aryl group Ar = C(6)F(5) or p-X-C(6)H(4) and X = CF(3), H, CH(3), and OCH(3). The results afford a number of significant inisights. (1) The RR (and IR) results show that at least two and possibly more high-frequency bands in the 1400-1550 cm(-1) region exhibit significant frequency downshifts on beta-octabromination and, thus, qualify as structure-sensitive marker bands. DFT geometry optimizations indicate that the saddled conformation should be clearly preferred for the beta-octabromo-meso-triarylcorrole derivatives studied and that beta-octabromination results in expansion of a number of skeletal bond distances of the corrole macrocycle, consistent with observed frequency downshifts. (2) Electrochemical measurements on planar Cu(III)[TArC] derivatives have shown that the para substituents on the meso-aryl groups exert a strong influence on the half-wave potentials for oxidation (rho(ox) = DeltaE(1/2ox)/Delta(3sigma) = 95 mV), suggesting that oxidation involves removal of an electron from the corrole "b(1)" HOMO, which has significant amplitudes at the meso postions and crudely resembles a porphyrin a(2u) HOMO in shape. In contrast, the Hammett rho(ox) is much lower for the nonplanar Cu(III)[Br(8)TArC] derivatives and we suggest that this ultimately results from a b(1)-to-a(2) HOMO reversal which in turn stems from a metal (d(x2-y2)-corrole ("b(1)") orbital interaction that becomes symmetry-allowed under a saddle distortion of the corrole macrocycle. In contrast to what has been observed for metallotetraphenylporphyrins, beta-octabromination dramatically raises the half-wave potential for one-electron oxidation of the triarylcorrole derivatives studied. This appears to be due to the fact that both the "a(2)" and "b(1)" HOMOs of a corrole (in C(2v) notation) have significantly higher amplitudes at the beta positions, compared to a porphyrin a(2u) HOMO. Thus, although many metallocorroles are significantly more easily oxidizable than analogous metalloporphyrins, certain beta-octahalogeno-meso-triarylcorrole derivatives can indeed be extremely electron deficient and oxidation resistant and may, therefore, find use as rugged catalysts or reagents under highly oxidizing conditions. (3) Finally, the Soret absorption maxima of high-valent metallotriarylcorroles exhibit a uniquely sensitive dependence on the substituents on the meso-aryl groups. Thus, on going from Cu(III)[T(p-CF(3)-P)C] (T(p-CF(3)-P)C = meso-tris((p-trifluoromethyl)phenyl)corrolato) to Cu(III)[T(p-OM-P)C] (T(p-OM-P)C = meso-tris(p-methoxyphenyl)corrolato), the Soret maximum red shifts by 26 nm, from 407 to 433 nm. Similarly, on going from Cu(III)[Br(8)T(p-CF(3)-P)C] (Br(8)T(p-CF(3)-P)C = beta-octabromo-meso-tris((p-trifluoromethyl)phenyl)corrolato) to Cu(III)[Br(8)T(p-OM-P)C] (Br(8)T(p-CF(3)-P)C = beta-octabromo-meso-tris(p-methoxyphenyl)corrolato), the Soret maximum red shifts by 34 nm, from 434 to 468 nm. Time-dependent DFT calculations suggest that this substituent dependence reflects significant ligand-to-metal charge-transfer character of certain transitions in the Soret region. The optical spectra of free-base and non-high-valent transition metal tetrapyrroles, in general, do not exhibit a similar substituent dependence. 相似文献
943.
4-Hydroxypyridine-2,6-dicarboxylic acid (chelidamic acid, cdaH2) reacts with Mn(OAc)2 x 4H2O to form a 1D staircase structure with dimeric Mn(II) units connected by water clusters to form a 3D framework, {[Mn2(cda)2 x 4H2O] x 4H2O}n, 1, in aqueous pyridine at room temperature. The compound crystallizes in the triclinic space group P1 with a = 9.495(3), b =10.733(5), c = 11.065(4) A, alpha = 87.42(5), beta = 74.14(5), gamma = 80.07(2) degrees, U = 1068.5(9) A3, Z = 2, rho(calcd) = 1.915 g cm(-3), T = 100 K, mu = 1.28 mm(-1), R1 = 0.0453 (I > 2sigma(I)), wR2 = 0.1046, GOOF = 1.282. Upon removal of the water molecules by heating, the 3D structure breaks down. Thermogravimetric analysis, infrared, X-ray powder diffraction studies, and X-ray crystallography were performed to characterize this compound. Since the coordination polymer has diaqua-bridged Mn(II) centers, it was subjected to variable-temperature magnetic studies. 相似文献
944.
Photopolymerization of methyl methacrylate was studied at 40° using dimethylaniline (DMA)—nitrobenzene (NB) C.T. complex as photoinitiator. Rp is proportional to ([DMA] [NB])0.24 and [M]1.0. Initiation of polymerization takes place through radicals generated by photodecomposition of DMA—NB complex formed in situ. Evidence for incorporation of N-methylanilonomethyl end-groups in the polymers was obtained by u.v. spectral analysis. The nonideal kinetics are explained in terms of significant participation of the initiating species in chain termination via degradative chain transfer. 相似文献
945.
Summary Like the silica gel the hydrogen ion concentration greatly influences the gelation of the product obtained in the metathesis
of the chloride of iron and chromium with sodium silicate. Time of gelation is minimum at a certain pH which shifts towards the acidic side with lowering in the concentration of the metathetic product. The gelation tendency
is ascribed to free silica present in it. At high concentration of the metallic chlorides no gelation is possible due to the
high peptising capacity of trivalent iron and chromium.
Zusammenfassung Wie beim Kiesels?ure-Gel hat die Wasserstoffionenkonzentration gro?en Einflu? auf die Gelatinierung der Reaktionsprodukte von Natriumsilikat mit Eisen- und Chromchlorid. Die Erstarrungszeit besitzt für ein bestimmtes pH ein Minimum, dessen Lage mit abnehmender Konzentration des Reaktionsproduktes nach der S?ureseite wandert. Die Gelatinierungstendenz wird der anwesenden freien Kiesels?ure zugeschrieben. Bei hohen Konzentrationen von Metallchloriden ist keine Gelatinierung m?glich infolge der hohen Peptisierungskraft von dreiwertigem Eisen und Chrom.相似文献
946.
Thepchatri P Cicero DO Monteagudo E Ghosh AK Cornett B Weeks ER Snyder JP 《Journal of the American Chemical Society》2005,127(37):12838-12846
Laulimalide is one of the newest naturally occurring macrolides known to act as a microtubule stabilizing agent with properties similar to Taxol. It also stands as being one of the most flexible with 18 rotatable bonds. This large number of rotatable bonds allows for approximately 3(18) potential conformers. To examine the conformational energy surface of laulimalide, we have performed an NAMFIS deconvolution analysis for laulimalide in DMSO-d6. The latter has been supplemented with a post-NAMFIS energy analysis at the Becke3LYP/6-31G level that examines the opposing effects of internal hydrogen bonding and syn-pentane interactions. In this way, we have identified 15 laulimalide conformations that can be classified into 5 different families: Supine, Convex, Cobra, Stretch, and Concave motifs. 相似文献
947.
948.
Summary A group of mixed-tris chelates of osmium(III) and osmium(IV) of type [OsAQ2]0/1 + [HA = glycine (glyH), picolinic acid (PicH) and quinaldic acid (qndH); HQ = 8-quinolinol] were prepared and characterized by physicochemical, magnetic and spectroscopic methods. The complexes exhibit several spin-allowed and spin-forbidden absorption bands and shoulders in the 200–700 nm region. The new chelates are electroactive and display nearly reversible OsIV-OsIII and OsIII-OsII couples in the ca. –1.1 to +0.3 V range versus s.c.e. The stability of metal oxidation states is discussed in terms of the electrochemical results. 相似文献
949.
Dipak C. Ghosh 《Czechoslovak Journal of Physics》1980,30(9):992-995
This work presents a study on the dependence of mean slow particle multiplicity (Nh) on the mass numberA of the target nucleus for a wide range of target mass and energy. It has been shown that this dependence can be best expressed by the relation N
h= 0.57A0.61.The author would like to express his indebtedness to Prof. A. Herz (CERN), Prof. K. D. Tolostov (JINR), Prof. R. Wilkes (University of Washington) for kindly supplying the exposed emulsion plates. 相似文献
950.
R. Lorenz A. Lande W. Biltz F. M. Jaeger B. Kapma E. D. Eastman E. Neuberg C. A. Kraus W. W. Luccase M. Neuberg W. W. Lucasse M. Abribat C. Marie W. A. Noyos Jr. P. A. Thiesen J. L. R. Morgan O. M. Lammer H. Remy P. Walden F. A. Smith H. I. Schlesinger F. H. Reed C. de Rhoden J. Ch. Ghosh 《Analytical and bioanalytical chemistry》1928,75(3-4):123-128