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761.
Gómez-Ruiz S Zahn S Kirchner B Böhlmann W Hey-Hawkins E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(29):8980-8985
One equivalent of [Na2(thf)5-(P4Ph4)] (1) reacts with one equivalent of [Ni(cod)2] (cod=1,5-cyclooctadiene) to give the unexpected ionic compound [Na(Et2O)3][Na3(Et2O)2Ni3(micro-P2Ph2)2-(P2Ph2)3] (2), whereas the reaction of [Ni(cod)2] with the less reactive [K2(pmdeta)2(P4Ph4)] (3) leads to the formation of [K(pmdeta)]2[Ni(P4Ph4)-(P2Ph2)] (4) (PMDETA=NMe(CH2CH2NMe2)2), in which K--Ni interactions are observed. The calculations for 4 confirm the structural parameters obtained by X-ray diffraction studies. A shared electron number (SEN) analysis was applied to investigate the K...Ni interactions. These studies indicate a SEN value of a typical three-center, two-electron bond for K1-Ni-K2 indicating a covalent contribution in the interaction between nickel and potassium. 相似文献
762.
S Henkel YA Huynh P Neuhaus M Winkler W Sander 《Journal of the American Chemical Society》2012,134(32):13204-13207
1-Azulenylcarbene was synthesized by photolysis of 1-azulenyldiazomethane in argon or neon matrices at 3-10 K. The highly polar singlet carbene is only metastable and undergoes a tunneling rearrangement to 8-methylene-bicyclo[5.3.0]deca-1,3,5,6,9-pentaene. After substitution of the 4 and 8 positions with deuterium, the rearrangement is completely inhibited. This indicates a very large kinetic isotope effect, as expected for a tunneling reaction. 相似文献
763.
764.
The synthesis and structural characterization of the tetramesityltetraphosphanide anion, (P4HMes4)- (1), is described. It is shown that 1 partially decomposes in solution and displays an unsymmetrical structure in which, depending on conditions, the proton may or may not fluctuate between the terminal P atoms of the P4 chain. 相似文献
765.
Charlot MF Pellegrin Y Quaranta A Leibl W Aukauloo A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(3):796-812
Excited states of ruthenium polypyridine-type complexes have always attracted the interest of chemists. We have recently found evidence of a remarkable long-lived excited state (30 micros) for a Ru(II) complex containing a heteroditopic ligand that can be viewed as a fused phenanthroline and salophen ligand.1 To unravel this intriguing electronic property, we have used density functional theory (DFT) calculations to understand the ground-state properties of [(bpy)(2)Ru(LH(2))](2+), where LH(2) represents N,N'-bis(salicylidene)-(1,10-phenanthroline)diamine. Excited singlet and triplet states have been examined by the time-dependent DFT (TDDFT) formalism and the theoretical findings have been compared with those for the parent complex [Ru(bpy)(3)](2+). The outstanding result is the presence of excited states lower in energy than the metal-to-ligand charge-transfer states, originating from intraligand charge transfer (ILCT) from the phenolic rings to the phenanthroline part of the coordinated LH(2). The spin density distribution for the lowest triplet state provides evidence that it is in fact the lowest triplet state of the free ligand. Correlation between the energy level diagram of orbitals for the ground state and that for the (3)ILCT state clearly establishes that the ruthenium retains its formal Ru(II) oxidation state. The quenching of the luminescence and the evidence of the long-lived excited state observed for [(bpy)(2)Ru(LH(2))](2+) are discussed in the light of the computational results. 相似文献
766.
767.
Julian Laackmann Winfried Säckel Lina Cepelyte Kamil Walag Robert Sedelmayer Franz Keller Werner Pauer Hans-Ulrich Moritz Ulrich Nieken 《Macromolecular Symposia》2011,302(1):235-244
Summary: Acoustic levitation was investigated as a model for spray processes. The influence of different parameters on the drying process of aqueous polyvinylpyrrolidone (PVP) solutions was studied and compared to the evaporation of water. The adequacy of acoustic levitation as model for spray processes was demonstrated. Experiments with water and aqueous PVP solutions indicated no dependency of the droplet size on the drying process for droplets with a diameter between 300 µm and 1.5 mm. Particles dried in an acoustic levitator displayed good accordance of morphology with those obtained in a spray tower. Surprisingly the addition of PVP to water resulted in faster evaporation of the solvent. Mathematical models of single droplets within a spray process typically refer to spherically symmetric droplet geometries. The simulation of other morphologies and their evolution throughout the process is still very challenging. A new drying model based on a fully three-dimensional meshfree approach is under development and shows good agreement to basic established models regarding the drying of a single droplet. 相似文献
768.
We deal with decay and boundedness properties of elements of radial subspaces of homogeneous Besov and Triebel-Lizorkin spaces. For the region of parameters which are of interest for us these homogeneous spaces are larger than the inhomogeneous counterparts. By switching from the inhomogeneous spaces to the homogeneous classes the properties of the radial elements change. Our investigations are based on the atomic decompositions for radial subspaces in the sense of Epperson and Frazier (J.?Fourier Anal Appl. 1:311?C353, 1995). Finally, we apply these results for deriving some assertions on compact embeddings on unbounded domains. 相似文献
769.
William C. Neuhaus Marisa C. Kozlowski 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(20):7916-7921
A facile method to oxidatively trimerize phenols using a catalytic aerobic copper system is described. The mechanism of this transformation was probed, yielding insight that enabled cross-coupling trimerizations. With this method, the natural product pyrolaside B was synthesized for the first time. The key strategy used for this novel synthesis is the facile one-step construction of a spiroketal trimer intermediate, which can be selectively reduced to give the natural product framework without recourse to stepwise Ullmann- and Suzuki-type couplings. As a result, pyrolaside B can be obtained expeditiously in five steps and 16 % overall yield. Three other analogues were synthesized, thus highlighting the utility of the method, which provides new accessibility to this area of chemical space. A novel xanthene was also synthesized through controlled Lewis acid promoted rearrangement of a spiroketal trimer. 相似文献
770.
Dr. Michał Rams Aleksej Jochim Michael Böhme Dr. Thomas Lohmiller Magdalena Ceglarska Dr. Marek M. Rams Dr. Alexander Schnegg Prof. Dr. Winfried Plass Prof. Dr. Christian Näther 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(13):2837-2851
The cobalt(II) in [Co(NCS)2(4-methoxypyridine)2]n are linked by pairs of thiocyanate anions into linear chains. In contrast to a previous structure determination, two crystallographically independent cobalt(II) centers have been found to be present. In the antiferromagnetic state, below the critical temperature (Tc=3.94 K) and critical field (Hc=290 Oe), slow relaxations of the ferromagnetic chains are observed. They originate mainly from defects in the magnetic structure, which has been elucidated by micromagnetic Monte Carlo simulations and ac measurements using pristine and defect samples. The energy barriers of the relaxations are Δτ1=44.9(5) K and Δτ2=26.0(7) K for long and short spin chains, respectively. The spin excitation energy, measured by using frequency-domain EPR spectroscopy, is 19.1 cm−1 and shifts 0.1 cm−1 due to the magnetic ordering. Ab initio calculations revealed easy-axis anisotropy for both CoII centers, and also an exchange anisotropy Jxx/Jzz of 0.21. The XXZ anisotropic Heisenberg model (solved by using the density renormalization matrix group technique) was used to reconcile the specific heat, susceptibility, and EPR data. 相似文献