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排序方式: 共有794条查询结果,搜索用时 203 毫秒
171.
B. de Castro C. Freire M. Teresa Duarte M. F. Minas da Piedade I. C. Santos 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(4):370-372
In the title complex, trans‐{2,2′‐[cyclohexane‐1,2‐diylbis(nitrilomethylidyne)]diphenolato‐κ4O,N,N′,O′}nickel(II)–chloroform (1/1), [Ni(C20H20N2O2)]·CHCl3, the Ni atom has a square‐planar geometry, slightly tetrahedrally distorted. The Ni—N and Ni—O bonding distances are within the expected ranges for Ni–Schiff base derivatives. The diimine bridge has a gauche conformation with the cyclohexyl ring almost coplanar with the NiN2O2 plane. The complex molecules pack in dimers with an Ni?Ni distance of 3.59 (1) Å and form a three‐dimensional structure displaying a herring‐bone configuration. Channels are occupied by solvent molecules, which are involved in C—H?O hydrogen bonds with the ligand O atoms. 相似文献
172.
173.
Guanaes Lais Danciguer Guimarães Matheus Murmel Ducatti Diogo R. B. Duarte Maria Eugênia R. Barreira Sandra M. W. Noseda Miguel D. Gonçalves Alan Guilherme 《Chemistry of Heterocyclic Compounds》2021,57(12):1195-1203
Chemistry of Heterocyclic Compounds - In the present work, we have synthesized new molecular hybrids consisting of porphyrin ring system connected at the meso positions with phenyl groups and/or,... 相似文献
174.
175.
Inês C.B. Martins Mariana Sardo Tomaž Čendak José R.B. Gomes João Rocha M. Teresa Duarte Luís Mafra 《Magnetic resonance in chemistry : MRC》2019,57(5):243-255
Hydrogen bonds (HBs) play a key role in the supramolecular arrangement of crystalline solids and, although they have been extensively studied, the influence of their strength and geometry on crystal packing remains poorly understood. Here we describe the crystal structures of two novel protic gabapentin (GBP) pharmaceutical salts prepared with the coformers methanesulfonic acid (GBP:METHA) and ethanesulfonic acid (GBP:ETHA). This study encompasses experimental and computational electronic structure analyses of 1H NMR chemical shifts (CSs), upon in silico HB cleavage. GBP:METHA and GBP:ETHA crystal packing comprise two main structural domains: an ionic layer (characterized by the presence of charge-assisted +NHGBP⋯ O−METHA/ETHA HB interactions) and a neutral layer generated in a different way for each salt, mainly due to the presence of bifurcated HB interactions. A comprehensive study of HB networks is presented for GBP:METHA, by isolating molecular fragments involved in distinct HB types (NH⋯ O, OH⋯ O, and CH⋯ O) obtained from in silico disassembling of an optimized three-dimensional packing structure. Formation of HB leads to calculated 1H NMR CS changes from 0.4 to ~5.8 ppm. This study further attempts to assess how 1H NMR CS of protons engaged in certain HB are affected when other nearby HB, involving bifurcated or geminal/vicinal hydrogen atoms, are removed. 相似文献
176.
177.
S. F. J. Cox J. S. Lord S. P. Cottrell H. V. Alberto J. M. Gil J. Piroto Duarte R. C. Vilão A. Keren D. Prabhakaran 《Hyperfine Interactions》2004,158(1-4):313-316
Muonium centres in Cu2O, Ag2O and CdO show hyperfine parameters spanning four orders of magnitude. They exemplify the three different categories of hydrogen
defect centre in semiconducting and dielectric solids, with very different electronic structure and electrical activity, namely
quasi-atomic (possibly deep acceptor), deep donor and shallow donor. 相似文献
178.
F.J Duarte 《Optics & Laser Technology》1997,29(8):3038-516
Solid-state multiple-prism near grazing-incidence grating dye lasers have been configured in cavities as short as 73 mm using dye-doped modified PMMA gain media. Single-longitudinal-mode emission, in near-Gaussian temporal pulses of 6-7 ns (FWHM) duration, has been achieved. Measured laser linewidths are in the 375 MHz range, and beam divergence is 2.3 mrad, at 3%-4% conversion efficiencies. 相似文献
179.
Georg Junker John R. Klauder 《The European Physical Journal C - Particles and Fields》1998,4(1):173-183
The quantization of systems with first- and second-class constraints within the coherent-state path-integral approach is
extended to quantum systems with fermionic degrees of freedom. As in the bosonic case the importance of path-integral measures
for Lagrange multipliers, which in this case are in general expected to be elements of a Grassmann algebra, is emphasized.
Several examples with first- and second-class constraints are discussed.
Received: 28 May 1997 / Revised version: 23 July 1997 相似文献
180.