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111.
Hanna C. Wentz Grigorii Skorupskii Ana B. Bonfim Jenna L. Mancuso Christopher H. Hendon Evan H. Oriel Graham T. Sazama Michael G. Campbell 《Chemical science》2020,11(5):1342
Redox-active metal–organic frameworks (MOFs) are promising materials for a number of next-generation technologies, and recent work has shown that redox manipulation can dramatically enhance electrical conductivity in MOFs. However, ligand-based strategies for controlling conductivity remain under-developed, particularly those that make use of reversible redox processes. Here we report the first use of ligand n-doping to engender electrical conductivity in a porous 3D MOF, leading to tunable conductivity values that span over six orders of magnitude. Moreover, this work represents the first example of redox switching leading to reversible conductivity changes in a 3D MOF.Redox-active ligands are used to reversibly tune electrical conductivity in a porous 3D metal–organic framework (MOF). 相似文献
112.
Assembly of well-aligned multiwalled carbon nanotubes in confined polyacrylonitrile environments: electrospun composite nanofiber sheets 总被引:5,自引:0,他引:5
Ge JJ Hou H Li Q Graham MJ Greiner A Reneker DH Harris FW Cheng SZ 《Journal of the American Chemical Society》2004,126(48):15754-15761
Highly oriented, large area continuous composite nanofiber sheets made from surface-oxidized multiwalled carbon nanotubes (MWNTs) and polyacrylonitrile (PAN) were successfully developed using electrospinning. The preferred orientation of surface-oxidized MWNTs along the fiber axis was determined with transmission electron microscopy and electron diffraction. The surface morphology and height profile of the composite nanofibers were also investigated using an atomic force microscope in tapping mode. For the first time, it was observed that the orientation of the carbon nanotubes within the nanofibers was much higher than that of the PAN polymer crystal matrix as detected by two-dimensional wide-angle X-ray diffraction experiments. This suggests that not only surface tension and jet elongation but also the slow relaxation of the carbon nanotubes in the nanofibers are determining factors in the orientation of carbon nanotubes. The extensive fine absorption structure detected via UV/vis spectroscopy indicated that charge-transfer complexes formed between the surface-oxidized nanotubes and negatively charged (-CN[triple bond]N:) functional groups in PAN during electrospinning, leading to a strong interfacial bonding between the nanotubes and surrounding polymer chains. As a result of the highly anisotropic orientation and the formation of complexes, the composite nanofiber sheets possessed enhanced electrical conductivity, mechanical properties, thermal deformation temperature, thermal stability, and dimensional stability. The electrical conductivity of the PAN/MWNT composite nanofibers containing 20 wt % nanotubes was enhanced to approximately 1 S/cm. The tensile modulus values of the compressed composite nanofiber sheets were improved significantly to 10.9 and 14.5 GPa along the fiber winding direction at the MWNT loading of 10 and 20 wt %, respectively. The thermal deformation temperature increased with increased MWNT loading. The thermal expansion coefficient of the composite nanofiber sheets was also reduced by more than an order of magnitude to 13 x 10(-6)/ degrees C along the axis of aligned nanofibers containing 20 wt % MWNTs. 相似文献
113.
Paul L. Coe Simon E. Sellers J.Colin Tatlow Graham Whittaker 《Journal of fluorine chemistry》1980,16(6):612
As part of a programme to prepare and evaluate a series of perfluoro- chemicals for use as inert fluids, the fluorinations of some tetrafluoroethylene oligomers over cobalt (III) fluoride have been studied.Fluorination of perfluoro-3,4-dimethylhex-3-ene (tetramer) and perfluoro-4-ethyl-3,4-dimethylhex-2-ene (pentamer) over CoF3 at 230°C and l45°C respectively afforded the corresponding saturated fluorocarbons however, at 250°C, pentamer gave predominantly the saturated tetramer. The thermal behaviour of these saturated fluorocarbons alone and in the presence of bromine and toluene has been studied.Pyrolysis of pentamer over glass beads at 500°C gave perfluoro-1,2,3- trimethylcyclobutene and isomers of perfluoro-2,3-dimethylpenta-1,3- diene. Under similar conditions perfluoro-2-(1-ethyl-1-methylpropyl). 3-methylpent-1-ene (hexamer) gave perfluoro-1-methyl-2-(1-methyl- propyl)-cyclobut-1-ene and perfluoro-2-methyl-3-(1-methylpropyl)-buta- 1,3-diene.These reactions and the structural elucidation of the products will be discussed. 相似文献
114.
Robert Graham 《Zeitschrift für Physik B Condensed Matter》1977,26(3):281-290
A method is given for the derivation of a path integral representation of the Green's function solutionP of equationsP/t=L
P,L being some Liouville operator. The method is applied to general diffusion processes.Feynman's path integral representation of the Schrödinger equation and Stratonovich's path integral representation of multivariate Markovian processes are obtained as special cases if the metric of the general diffusion process is flat. For curved phase spaces our result is a nontrivial generalization and new. New applications e.g. to quantized motion in general relativity, to transport processes in inhomogeneous systems, or to nonlinear non-equilibrium thermodynamics are made possible. We expect applications to be fruitfull in all cases where (continuous) macroscopic transport processes in Riemann geometries have to be considered. 相似文献
115.
G. F. Gantefor D. M. Cox A. Kaldor 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,19(4):59-61
In this paper we describe the application of a special form of electron photodetachment spectroscopy, zero electron kinetic energy (ZEKE) spectroscopy, to the study of cold metal cluster anions. From this study we have obtained vibrational and thus structural information of several neutral and charged clusters, e.g. Au 2 ?/0 , Ag 3 ?/0 , Sn 2 ?/0 and Al 3 ?/0 . In addition, in separate measurements of the relative photodetachment cross section of Au 2 ? , we have discovered sharp resonances which are due to electronic autodetachment from a short lived excited state. 相似文献
116.
117.
Shengfei Jin Hang T. Dang Graham C. Haug Viet D. Nguyen Hadi D. Arman Oleg V. Larionov 《Chemical science》2020,11(34):9101
Construction of C–C bonds at the α-carbon is a challenging but synthetically indispensable approach to α-branched carbonyl motifs that are widely represented among drugs, natural products, and synthetic intermediates. Here, we describe a simple approach to generation of boron enolates in the absence of strong bases that allows for introduction of both α-alkyl and α-aryl groups in a reaction of readily accessible 1,2-dicarbonyls and organoboranes. Obviation of unselective, strongly basic and nucleophilic reagents permits carrying out the reaction in the presence of electrophiles that intercept the intermediate boron enolates, resulting in two new α-C–C bonds in a tricomponent process.α-Branched carboxylic acids and other carbonyls are readily accessed by a metal- and base-free deoxygenative α-alkylation and α-arylation of 1,2-dicarbonyls via boron enolates, resulting in a tricomponent coupling with unconventional electrophiles. 相似文献
118.
Graham A. Bowmaker Prof. Dr. Michael I. Bruce Brian W. Skelton Neil Somers Allan H. White 《无机化学与普通化学杂志》2007,633(7):1024-1030
The complexes [Cu2Br4]2?, [Cu2I4]2?, [Cu2I2Br2]2?, [Cu2I3Cl]2?, [Ag2Cl4]2? have been characterized as their isomorphous bis(triphenylphosphoranylidene)ammonium ([Ph3PNPPh3]+ = PNP+) salts by single crystal structural determinations. All anions show the centrosymmetric doubly halogen‐bridged forms [XM(μ‐X)2MX]2? with three‐coordinate metal atoms that have been observed in [M2X4]2? complexes with other large organic cations. In [Cu2I2Br2]2? the iodide ligands occupy the bridging positions and the bromide the terminal positions, while in [Cu2I3Cl]2?, obtained in an attempt to prepare [Cu2I2Cl2]2?, two of the iodide ligands occupy the bridging positions with the third iodide and the chloride ligand occupying two statistically disordered terminal positions. In [Ag2Cl4]2? the distortion from ideal trigonal coordination of the metal atom is greater than in the copper complexes, but less than in other previously reported [Ag2Cl4]2? complexes with organic cations. The ν(MX) bands have been assigned in the far‐IR spectra, and confirm previous observations regarding the unexpectedly simple IR spectra of [Cu2X4]2? complexes. 相似文献
119.
Winter R Nixon PG Gard GL Graham DJ Castner DG Holcomb NR Grainger DW 《Langmuir : the ACS journal of surfaces and colloids》2004,20(14):5776-5781
Recently synthesized (Winter, R.; Nixon, P. G.; Gard, G. L.; Radford, D. H.; Holcomb, N. R.; Grainger, D. W. J. Fluorine Chem. 2001, 107, 23-30) SF5-terminated perfluoroalkyl thiols (SF5(CF2)nCH2CH2SH, where n = 2, 4, and 6) and a symmetric SF5-terminated dialkyl disulfide ([SF5-CH=CH-(CH2)8-S-]2) were assembled as thin films chemisorbed onto gold surfaces. The adsorbed monolayer films of these SF5-containing molecules on polycrystalline gold were compared using ellipsometry, contact angle, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and infrared spectroscopy (FTIR) surface analytical methods. The resulting SF5-dialkyl disulfide monolayer film shows moderate angle dependence in depth-dependent XPS analysis, suggesting a preferentially oriented film. The SF5-terminated perfluoroalkyl thiols exhibit angular-dependent XPS compositional variance depending on perfluoroalkyl chain length, consistent with improved film assembly (increasingly hydrophobic, fewer defects, and more vertical chain orientation increasing film thickness) with increasing chain length. Tof-SIMS measurements indicate that both full parent ions for these film-forming molecules and the unique SF5 terminal group are readily detectable from the thin films without substantial contamination from other adsorbates. 相似文献
120.
Shigang Zhang Brigitte Schindler Graham Nicholson Ernst Bayer 《Journal of separation science》1995,18(9):579-581
Residual adsorptive activity of reversed phase (RP) column packings used in supercritical fluid chromatography (SFC) can be significantly reduced by a dynamic in-situ silanization with diphenyltetramethyldisilazane (DPTMDS). RP-materials thus deactivated were characterized both chromatographically and by solid-phase 29Si NMR. 相似文献