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961.
Fox JP Ramdhanie B Zareba AA Czernuszewicz RS Goldberg DP 《Inorganic chemistry》2004,43(21):6600-6608
As part of our efforts to develop the transition metal chemistry of corrolazines, which are ring-contracted porphyrinoid species most closely related to corroles, the vanadium and copper complexes (TBP)(8)Cz(H)V(IV)O (1) and (TBP)(8)CzCu(III) (2) of the ligand octakis(para-tert-butylphenyl)corrolazine [(TBP)(8)Cz] have been synthesized. The coordination behavior, preferred oxidation states, and general redox properties of metallocorrolazines are of particular interest. The corrolazine ligand in 1 was shown to contain a labile proton by acid/base titration and IR spectroscopy, serving as a -2 ligand rather than as the usual -3 donor. The oxidation state of the vanadium center in 1 was shown to be +4, in agreement with the overall neutral charge for this complex. The EPR spectrum of 1 reveals a rich signal consistent with a V(IV)(O) (d(1), S = 1/2) porphyrinoid species (g(xx) = 1.989, g(yy) = 1.972, g(zz) = 1.962). The electrochemical analysis of 1 shows behavior closer to that of a porphyrazine than a corrolazine, with a positively shifted, irreversible reduction at -0.65 V (vs Ag/AgCl). Resonance Raman and IR data for 1 confirm the presence of a triply bonded terminal oxo ligand with nu(V(16)O) = 975 cm(-1) and nu(V(18)O) = 939 cm(-1). The copper complex 2 exhibits a diamagnetic (1)H NMR spectrum, indicative of a bona fide square planar copper(III) (d(8), low-spin) complex. Previously reported copper corroles have been characterized as copper(III) complexes which exhibit a paramagnetic NMR spectrum at higher temperatures, indicative of a thermally accessible triplet excited state ([(corrole(*+))Cu(II)]). The NMR spectrum for 2 shows no paramagnetic behavior in the range 300-400 K, indicating that compound 2 does not have a thermally accessible triplet excited state. These data show that the corrolazine system is better able to stabilize the high oxidation state copper center than the corresponding corroles. Electrochemical studies of 2 reveal two reversible processes at +0.93 and -0.05 V, and bulk reduction of 2 with NaBH(4) generates the copper(II) species [(TBP)(8)CzCu(II)](-) (2a), which exhibits an EPR signal typical of a copper(II) porphyrinoid species. 相似文献
962.
The basic structure of benzaldehyde photopolymer (BPOL) consists of phenyl groups attached to a carbon-carbon and carbon-oxygen chain. The average BPOL molecule contains 12 monomer units. Relative rates for the BPOL photosensitized dimerization of 1,3-cyclohexadiene and the isomerizations of the 1,3-pentadienes, cis-1,2-dichloroethylene and cis-2-butene are reported. The BPOL photosensitized isomerizations of the 1,3-pentadienes in the visible (λ > 395 nm) proceed by a simple mechanism. Stern-Volmer plots are linear and the photostationary trans/cis ratio is 2.0, independent of 1,3-pentadiene pressure over the range 2–180 Torr. The energy of the BPOL triplet state is less than but near 53 kcal mol?1. It excites the s-cis 1,3-pentadiene rotamers exclusively. The decay ratio of the s-cis triplets is 3.75. 相似文献
963.
In a public health system, one of the problems is the size of the waiting list for admission to hospital. This research involves establishing a method of analysing the general surgery waiting list problem at hospital and district level. While there are many aspects to such a study, this paper concentrates on a linear programming model to plan the aggregate throughput of the general surgical department. Preliminary results from applying the techniques to actual health districts in the United Kingdom are reported. 相似文献
964.
Colin D. Fox 《Algebra Universalis》1983,16(1):163-166
The containmentS
nL
n is proper. (Here n2 is a positive integer,S
n is the small variety of lattice-ordered groups of Scrimger andL
n is the variety of lattice-ordered groups defined by the law anbn=bnan.) Jo E. Smith proved this result for n a composite integer. In this note we proveS
nL
n when n is prime.Presented by L. Fuchs. 相似文献
965.
The molecular structures of two carbaboranes, closo-2,3-C(2)B(9)H(11) and nido-2,9-C(2)B(9)H(13), were determined experimentally for the first time using gas-phase electron diffraction (GED). For closo-2,3-C(2)B(9)H(11), a model with C(2)(v)() symmetry was refined to give C-B bond distances ranging 158.3-167.0 pm and B-B distances ranging 177.4-200.0 pm. The structure of nido-2,9-C(2)B(9)H(13) was refined using a model with C(s)() symmetry to give C-B bond lengths ranging 160.3-171.9 pm and B-B lengths ranging 173.0-196.1 pm. Ab initio computations (up to MP2/6-311+G) were also carried out on these and the related nido-7,8-C(2)B(9)H(13), which was not sufficiently stable to allow determination of its molecular structure by GED. 相似文献
966.
H. Yamashita H. Nishiguchi N. Kamada M. Anpo Y. Teraoka H. Hatano S. Ehara K. Kikui L. Palmisano A. Sclafani M. Schiavello M. A. Fox 《Research on Chemical Intermediates》1994,20(8):815-823
Photoinduced reduction of CO2 by H2O to produce CH4 and CH3OH has been investigated on wellcharacterized standard TiO2 catalysts and on a Cu2+ loaded TiO2 catalyst. The efficiency of this photoreaction depends strongly on the kind of catalyst and the ratio of H2O to CO2. Anatase TiO2, which has a large band gap and numerous surface OH groups, shows high efficiency for photocatalytic CH4 formation. Photogenerated Ti3+ ions, H and CH3 radicals are observed as reactive intermediates, by ESR at 77 K. Cu-loading of the small, powdered TiO2 catalyst (Cu/TiO2) brings about additional formation of CH3OH. XPS studies suggest that Cu+ plays a significant role in CH3OH formation. 相似文献
967.
Charge transfer (CT) interaction is described in semiconducting dispersions of TCNQ complex salt \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Et}_3 {\rm NH}^+ ({\rm TCNQ})_2^{\cdot^{\hskip-3.7pt\hbox{--}}}$\end{document} with and without added TCNQ°, in poly(vinyl acetal) matrices in which the electron-donor moiety is varied. The extent of CT interaction was determined in films and in solution (DMF, acetonitrile, or methylene chloride) through the absorbances at 398 nm (\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm TCNQ}{\ }^{\cdot^{\hskip-3.7pt\hbox{--}}}$\end{document} and TCNQ°) and 857 nm \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm TCNQ}{\ }^{\cdot^{\hskip-3.7pt\hbox{--}}}$\end{document}. Resistivity of the conductive films was related to the stoichiometry of TCNQ species in the films and found to have a minimum at \documentclass{article}\pagestyle{empty}\begin{document}$[{\rm TCNQ}^\circ]/[{\rm TCNQ}{\ }^{\cdot^{\hskip-3.7pt\hbox{--}}}]\simeq 1$\end{document}. Lower resistivities were attained with films having a uniform, densely packed dispersion of microcrystallites which were obtained at a relatively slow solvent removal rate. With this particular complex salt, strong electron-donor polymers are found to be better matrices for semiconductivity. 相似文献
968.
Marso M. Fox A. Heidelberger G. Kordos P. Luth H. 《Electron Device Letters, IEEE》2006,27(12):945-947
In this letter, the performance of AlGaN/GaN-based metal-semiconductor-metal (MSM) varactor diodes based on HFET and MOSHFET layer systems is investigated. Passivated HFET MSM devices are coated with a 10-nm-thick SiO2 layer between the electrodes; in MOSHFET-based diodes, this layer is also used as an insulator underneath the gate. Device fabrication uses standard HFET fabrication technology, allowing easy integration in monolithic microwave integrated circuits. Devices with different electrode geometry are characterized by direct current and by S-parameter measurements up to 50 GHz. The HFET-based varactors show capacitance ratios up to 14 and cutoff frequencies up to 74 GHz. The MOSHFET-based devices, on the other hand, show lower capacitance ratios and poorer stability because of the insulation layer between electrodes and semiconductor 相似文献
969.
We generated pulsed quadrature-squeezed light by cross-phase modulation in single-crystal hexagonal CdSe at wavelengths of 1.4 to 1.55mum . We measured 0.4-dB squeezing (0.7 dB is inferred at the crystal) with 100-fs laser pulses. The wavelength and the intensity dependence, as well as variations in the local oscillator configuration, are examined. At higher intensities squeezing is shown to deteriorate owing to competing nonlinear processes. 相似文献
970.