Search results for " Structure"
showing 10 items of 25475 documents
The Preparation of Diaryl Sulfoxonium Triflates and Their Application in Palladium‐Catalyzed Cross‐Coupling Reactions
2022
Chemistry 17(19), e202200828 (2022). doi:10.1002/asia.202200828
Last millennium northern hemisphere summer temperatures from tree rings: Part I: The long term context
2016
Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала. Large-scale millennial length Northern Hemisphere (NH) temperature reconstructions have been progressively improved over the last 20 years as new datasets have been developed. This paper, and its companion (Part II, Anchukaitis et al. in prep), details the latest tree-ring (TR) based NH land air temperature reconstruction from a temporal and spatial perspective. This work is the first product of a consortium called N-TREND (Northern Hemisphere Tree-Ring Network Development) which brings together dendroclimatologists to identify a collective strategy for improving large-scale summer temperature reconstructions…
The giant panda is cryptic
2021
The giant panda (Ailuropoda melanoleuca) is an iconic mammal, but the function of its black-and-white coloration is mysterious. Using photographs of giant pandas taken in the wild and state-of-the-art image analysis, we confirm the counterintuitive hypothesis that their coloration provides camouflage in their natural environment. The black fur blends into dark shades and tree trunks, whereas white fur matches foliage and snow when present, and intermediate pelage tones match rocks and ground. At longer viewing distances giant pandas show high edge disruption that breaks up their outline, and up close they rely more on background matching. The results are consistent across acuity-corrected c…
Ag44(EBT)26(TPP)4 Nanoclusters with Tailored Molecular and Electronic Structure
2021
Although atomically precise metalloid nanoclusters (NCs) of identical size with distinctly different molecular structures are highly desirable to understand the structural effects on the intriguing optical and photophysical properties, their synthesis remains highly challenging. Herein, we employed phosphine and thiol capping ligands featuring appropriate steric effects and synthesized a charge‐neutral Ag NC with the formula, Ag 44 (EBT) 26 (TPP) 4 (EBT: 2‐ethylbenzenethiolate; TPP: triphenylphosphine). The single‐crystal X‐ray structure reveals that this NC has a hollow metal core of Ag 12 @Ag 20 and a metal‐ligand shell of Ag 12 (EBT) 26 (TPP) 4 . The presence of mixed ligands and long V‐…
Silica powder obtained by sol-gel method as a support of organometallic vanadium catalyst for ethylene polymerization
2004
Sol-gel technique was employed to obtain the silica-type powder, which after modification procedure was applied as asupport of organometallic catalytic system for ethylene polymerization. The powder product was synthesized using hydrolysis and condensation of TEOS, catalyzed by ammonia. Obtained material and a reference support (commercial silica Davisil) were characterized to determine their particle size distributions, BET surface area, pore volume and diameter. Gas-phase adsorption of vanadium catalyst on analyzed support materials as well as adsorption from the solution in hexane were carried out. Both carrier materials were thermally pretreated prior catalytic systems syntheses and the…
6-Methyluracil: a redetermination of polymorph (II)
2019
6-Methyluracil, C5H6N2O2, exists in two crystalline phases: form (I), monoclinic, space group P21/c [Reck et al. (1988). Acta Cryst. A44, 417–421] and form (II), monoclinic, space group C2/c [Leonidov et al. (1993). Russ. J. Phys. Chem. 67, 2220–2223]. The structure of polymorph (II) has been redetermined providing a significant increase in the precision of the derived geometric parameters. In the crystal, molecules form ribbons approximately running parallel to the c-axis direction through N—H...O hydrogen bonds. The radical differences observed between the crystal packing of the two polymorphs may be responsible in form (II) for an increase in the contribution of the polar canonical forms…
Theoretical investigation of the electronic structure of fullerenes
1994
Summary form only given. Research in the growing family of fullerene compounds are in continuous expansion. Much theoretical and experimental effort has been devoted to the study of the electronic properties these carbon cages present. However, although significant work has been done, the purpose of this paper is to provide a detailed theoretical analysis of the electronic properties of several fullerenes. We have calculated the electronic structure of these carbon cages within the valence effective Hamiltonian (VEH) approach. The calculated one-electron energy levels are correlated with experimental UPS spectra. The good correlation between calculated and experimental values shows VEH appr…
Uncertainty analysis and symmetry restoration in nuclear self-consistent methods
2015
This thesis contains two articles, in the following denoted by I and II, and an introduction to them. In Chapter 1, I present the theoretical models of nuclear structure. In Chapter 2, I introduce the basic ideas about the density functional theory (DFT) and self-consistent mean-field (SCMF) calculations. In Chapter 3, I give the formulae for the uncertainty propagation, which is the error analysis method used in article I. As a proper tool to survey the predictive power of theoretical models, the error analysis now has become more and more widely used. By analyzing the propagation of uncertainties, one tries to find out the e ectiveness of the calculation with a given parameter set obtaine…
CCDC 846271: Experimental Crystal Structure Determination
2012
Related Article: G.Callebaut, S.Mangelinckx, L.Kiss, R.Sillanpaa, F.Fulop, N.De Kimpe|2012|Org.Biomol.Chem.|10|2326|doi:10.1039/c2ob06637h
Thiophene based imino-pyridyl palladium(II) complexes : Synthesis, molecular structures and Heck coupling reactions
2017
The new compounds (5-methyl-2-thiophene-2-pyridyl(R))imine [R = methyl (L1); R = ethyl (L2)] and (5-bromo-2-thiophene-2-pyridyl(R)imine [R = methyl (L3); R = ethyl (L4)] were successfully synthesized via Schiff base condensation reaction and obtained in good yields. These potential ligands were reacted with [PdCl2(COD)] and [PdClMe(COD)] to give the corresponding complexes [PdCl2(L)] (L = L1-L4; 1–4) and [PdClMe(L)] (L = L1-L4; 5–8). All compounds were characterized by IR, 1H and 13C NMR spectroscopy, elemental analysis and mass spectrometry. The molecular structures of 1, 2, 6 and 8 were confirmed by X-ray crystallography. The complexes were evaluated as catalyst precursors for standard He…