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81.
meso-Pentafluorophenyl- substituted [40]nonaphyrin(1.1.1.1.1.1.1.1.1) 3 has been prepared by using a stepwise ring-size-selective synthesis, and has been reduced with NaBH(4) to [42]nonaphyrin(1.1.1.1.1.1.1.1.1) 5. Structurally, 3 is characterized by a figure-of-eight shape, consisting of a porphyrin-like tetrapyrrolic segment and a hexaphyrin-like hexapyrrolic segment, whereas 5 has been found to adopt a distorted nonplanar butterfly-like shape. In the mono-metal complexes 6 and 7, a Zn(II) or Cu(II) ion is bound by the porphyrin-like tetrapyrrolic segment, maintaining the overall structure of 3. Similarly to 3, complexes 6 and 7 are interconvertible with the corresponding complexes 9 and 10 through two-electron reduction with NaBH(4) and oxidation with DDQ. The metal-free hexaphyrin-like segments of 6 and 7 have been shown to serve as a suitable platform for the complexation of two palladium ions, providing hetero-trinuclear metal complexes 11 (Zn(II)-Pd(II)-Pd(II)) and 13 (Cu(II)-Pd(II)-Pd(II)) in high yields, in which the Zn or Cu ion resides at the same porphyrin-like segment, and one Pd ion is bound in an NNCC fashion through double C--H bond activation while the other is bound in an NNC fashion with single C--H bond activation. Multi-metal complexes 11, 12, and 13 exhibit small electrochemical HOMO-LUMO gaps (<0.6 eV), despite their nonplanar conformations. 相似文献
82.
Katsuhiro Munakata Kenji Harada Nobukazu Yoshikawa Masahide Itoh Shinsuke Umegaki Toyohiko Yatagai 《Optical Review》1999,6(6):518-521
Two fabrication methods of surface relief electro-optic (EO) gratings in azo-polymer films are described: surface deformation by a continuous wave laser and laser ablation by a pulse laser. In the fabrication process, the periodic intensity modulation of laser beams is formed by an interference fringe or a phase mask. The surface relief EO grating is fabricated by poling the surface relief grating (SRG) after the SRG fabrication process. The linear dependence of an applied voltage in the modulation efficiency of the first-order diffraction beam is observed. The proposed methods are effective for highly-efficient surface relief EO grating fabrication. 相似文献
83.
A silicon nitride fiber (Si3N4) was synthesized from polycarbosilane (PCS) fiber by radiation application. PCS fibers were cured by electron beam (EB) irradiation in a helium gas atmosphere prior to the pyrolysis. The cured PCS fiber was converted to Si3N4 ceramic fiber with flexibility by nitridation in ammonia gas at a high temperature of 500–1000°C. The obtained Si3N4 fibre showed a high heat resistance up to 1300°C, a high tensile strength of 2 GPa and excellent electrical resistivity of 1013 Ω cm. The ceramic fiber was fabricated to cloth and applied for electric wire insulator. The wire cable is flexible and can be applied at a high temperature atmosphere of around 1000°C. 相似文献
84.
We study the roles of quark-pair correlations for baryon properties, in particular on non-leptonic weak decay of hyperons. We construct the quark wave function of baryons by solving the three body problem explicitly with confinement force and the short range attraction for a pair of quarks with their total spin being 0. We show that the existence of the strong quark-quark correlations enhances the non-leptonic transition amplitudes which is consistent with the data, while the baryon masses and radii are kept to the experiment. 相似文献
85.
We prove the following theorem: For a connected noncomplete graph G, let τ(G): = min{dG(u) + dG(v)|dG(u, v) = 2}. Suppose G is a 3-connected noncomplete graph. Then through each edge of G there passes a cycle of length ≥ min{|V(G)|, τ (G) − 1}. © 1997 John Wiley & Sons, Inc. 相似文献
86.
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88.
It is well‐known that every planar graph has a vertex of degree at most five. Kotzig proved that every 3‐connected planar graph has an edge xy such that deg(x) + deg (y) ≤ 13. In this article, considering a similar problem for the case of three or more vertices that induce a connected subgraph, we show that, for a given positive integer t, every 3‐connected planar graph G with |V(G)| ≥ t has a connected subgraph H of order t such that Σx∈V(H) degG(x) ≤ 8t − 1. As a tool for proving this result, we consider decompositions of 3‐connected planar graphs into connected subgraphs of order at least t and at most 2t − 1. © 1999 John Wiley & Sons, Inc. J Graph Theory 30: 191–203, 1999 相似文献
89.
We propose a dry method of cleaning Ge(1 0 0) surfaces based on nitrogen plasma treatment. Our in situ Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED) analyses demonstrate that surface contamination remaining after wet treatment was effectively removed by nitrogen radical irradiation at low substrate temperatures. The nitrogen plasma cleaned Ge(1 0 0) surface shows a well-ordered 2 × 1 reconstruction, which indicates the formation of a contamination-free Ge(1 0 0) surface with good crystallinity. We discuss the possible reaction mechanism considering how chemisorbed carbon impurities are removed by selective C-N bond formation and subsequent thermal desorption. These findings imply the advantage of plasma nitridation of Ge surfaces for fabricating nitride gate dielectrics, in which we can expect surface pre-cleaning at the initial stage of the plasma treatment. 相似文献
90.
Harayama Y Yoshida M Kamimura D Wada Y Kita Y 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(18):4893-4899
Hypervalent iodine(III) reagents are readily available, easy to handle, and have a low toxicity and similar reactivities to those of heavy metal reagents, and hence they are used for various oxidative reactions. The oxidative cleavage of alkynes or carbonyl compounds by using bis(trifluoroacetoxy)iodo(III) pentafluorobenzene (C(6)F(5)I(OCOCF(3))(2)) has been reported. Herein, the efficient direct synthesis of N,O-acetal compounds as key intermediates of discorhabdin A, by the oxidative fragmentation reaction of alpha-amino acids or beta-amino alcohols by using C(6)F(5)I(OCOCF(3))(2), is described. 相似文献