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排序方式: 共有122条查询结果,搜索用时 15 毫秒
1.
The ligand‐exchange mechanism of solvated Be2+ cations has been studied by means of DFT calculations (RB3LYP/6‐311+G**). Ligand exchange around [BeL4]2+, where L=H2O, NH3, CO2, formaldehyde (H2CO), HCN, N2, and CO, was found to follow an associative interchange (Ia) process in all cases. The size of the activation barrier is almost independent of the type of donor atom, and depends mainly on the hybridization undergone by the donor atom. This, in turn, suggests that steric effects play a major role in solvent‐ and ligand‐exchange reactions in Be2+ systems. 相似文献
2.
Saalfrank RW Deutscher C Maid H Ako AM Sperner S Nakajima T Bauer W Hampel F Hess BA van Eikema Hommes NJ Puchta R Heinemann FW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(8):1899-1905
In the reaction of the N-substituted diethanolamines (H(2)L(1-3)) (1-3) with calcium hydride followed by addition of iron(III) or indium(III) chloride, the iron wheels [Fe(6)Cl(6)(L(1))(6)] (4) and [Fe(6)Cl(6)(L(2))(6)] (6) or indium wheels [In(6)Cl(6)(L(1))(6)] (5), [In(6)Cl(6)(L(2))(6)] (8) and [In(6)Cl(6)(L(3))(6)] (9) were formed in excellent yields. Exchange of the chloride ions of 6 by thiocyanate ions afforded [Fe(6)(SCN)(6)(L(2))(6)] (7). Whereas the structures of 4, 5 and 7 were determined unequivocally by single-crystal X-ray analyses, complexes 8 and 9 were characterised by NMR spectroscopy. Contrary to what is normally presumed, the scaffolds of six-membered metallic wheels are not generally rigid, but rather undergo nondissociative topomerisation processes. This was shown by variable temperature (VT) (1)H NMR spectroscopy for the indium wheel [In(6)Cl(6)(L(1))(6)] (5) and is highlighted for the enantiotopomerisation of one indium centre [ 1/6[S(6)-5]<==>[1/6[S(6)-5']]. The self-assembly of metallic wheels, starting from diethanolamine dendrons, is an efficient strategy for the convergent synthesis of metallodendrimers. 相似文献
3.
Jan-Christoph Eichler Robert A. Skutnik Anupam Sengupta Marco G. Mazza Martin Schoen 《Molecular physics》2019,117(23-24):3715-3733
Anisotropic fluids (e.g. liquid crystals) offer a remarkable promise as optofluidic materials owing to the directional, tunable, and coupled interactions between the material, flow, and the optical fields. Here we present a comprehensive in silico treatment of this anisotropic interaction by performing nonequilibrium molecular dynamics simulations. We quantify the response of a nematic liquid crystal (NLC) undergoing a Poiseuille flow in the Stokes regime, while being illuminated by a laser beam incident perpendicular to the flow direction. We adopt a minimalistic model to capture the interactions, accounting for two features: first, the laser heats up the NLC locally; and second, the laser polarises the NLC and exerts an optical torque that tends to reorient molecules of the nematic phase. Because of this reorientation the liquid crystal exhibits small regions of biaxiality, where the nematic director is one symmetry axis and the axis of rotation for the reorientation of the molecules is the other one. We find that the relative strength of the viscous and the optical torques mediates the flow-induced response of the biaxial regions, thereby tuning the emergence, shape and location of the regions of enhanced biaxiality. The mechanistic framework presented here promises experimentally tractable routes toward novel optofluidic applications based on material-flow-light interactions. 相似文献
4.
Snežana Jovanović Ralph Puchta Olivera Klisurić 《Journal of Coordination Chemistry》2016,69(5):735-747
The crystal structure of K[PtCl3(caffeine)] was determined. The coordination geometry around platinum is square-planar formed by N9 of the caffeine ligand and three Cl? ions. The bond lengths and angles of K[PtCl3(caffeine)] were compared with those reported for [PtCl3(caffeine)]? and K[PtCl3(theobromine)]. At the level of the statistical significance of the data we have compared, no differences in the bond distances and angles for any of these compounds were noticed. Weak interactions between K+ and Cl? are responsible for the formation of 1-D polymeric chains in the crystal structure of the complex. The interactions of K[PtCl3(caffeine)] with inosine (Ino) and guanosine-5′-monophosphate (5′-GMP) were studied by 1H NMR spectroscopy at 295 K in D2O in a molar ratio of 1 : 1. The results indicate formation of the reaction product [PtCl3(Nu)] (Nu=Ino or 5′-GMP) with the release of caffeine from the coordination sphere of the starting complex. The higher stability of the bond between the Pt(II) ion and Ino or 5′-GMP compared to the stability of the platinum–caffeine bond is confirmed by density functional theory calculations (B3LYP/LANL2DZp) using as models 9-methylhypoxanthine and 9-methylguanine. 相似文献
5.
6.
Tris(oxalato)phosphorus acid and its lithium salt 总被引:1,自引:0,他引:1
Wietelmann U Bonrath W Netscher T Nöth H Panitz JC Wohlfahrt-Mehrens M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(10):2451-2458
The conversion of three equivalents of anhydrous oxalic acid with phosphorus pentachloride yields tris(oxalato)phosphorus acid 1, which crystallizes from diethyl ether solutions as protonated diethyl ether complex [(Et2O)2H](+)[P(C2O3)3)]-. The superacidic compound can be used as catalyst for Friedel-Crafts-type reactions. Upon neutralization with lithium hydride, the lithium salt Li[P(C2O3)3] 2 is obtained, which is highly soluble in aprotic solvents and which exhibits a wide voltage window. Thus, the lithium compound is a promising candidate as electrolyte for high performance non-aqueous batteries. 相似文献
7.
Crystal Structure of [BeCl2(15‐Crown‐5)] Single crystals of [BeCl2(15‐crown‐5)] ( 1 ) were obtained from dichloromethane solutions of BeCl2 in the presence of the equivalent amount of 15‐crown‐5 and characterized by IR spectroscopy and X‐ray diffraction. Space group P21/c, Z = 4, lattice dimensions at 100 K: a = 1036.2(1), b = 1071.1(1), c = 1360.1(1) pm, β = 109.86(1)°, R1 = 0.0225. The structure determination shows no disorder, all hydrogen positions were refined isotropically. The results are in contrast to the previously reported crystal structure determination in the space group P21nb. The beryllium atom of 1 forms a BeO2C2 five‐membered heterocycle with terminal chlorine atoms to give a distorted tetrahedral coordination with distances Be–O 166.5(2), 169.9(2) pm, and Be–Cl 195.8(2), 197.8(2) pm. The structural results are in good agreement with DFT calculations on B3LYP/6‐311+G** level. 相似文献
8.
Thomas W. Müller Jan-Christoph Schlage-Puchta 《Abhandlungen aus dem Mathematischen Seminar der Universit?t Hamburg》2009,79(2):193-227
This paper continues the investigation of the groups
RF(G)\mathcal{RF}(G)
introduced and studied in [I.M. Chiswell and T.W. Müller, A class of groups with canonical ℝ-tree action, Springer LNM, to
appear]. Two new concepts, that of a test function, and that of a pair of locally incompatible (test) functions are introduced, and their theory is developed. As application, we obtain a number of new quantitative as
well as structural results concerning
RF(G)\mathcal{RF}(G)
and its quotient
RF(G)/E(G)\mathcal{RF}(G)/E(G)
modulo the subgroup E(G) generated by the elliptic elements. Among other things, the cardinality of
RF(G)\mathcal{RF}(G)
is determined, and it is shown that both
RF(G)\mathcal{RF}(G)
and
RF(G)/E(G)\mathcal{RF}(G)/E(G)
contain large free subgroups, and that their abelianizations both contain a large ℚ-vector space as direct summand. 相似文献
9.
We show that a large class of groups has normal subgroup growth of type nlog n, which is the same as the growth type of a free group of rank 2.Received: 21 June 2004 相似文献
10.
Laura Senft Jamonica L. Moore Alicja Franke Katherine R. Fisher Andreas Scheitler Achim Zahl Ralph Puchta Dominik Fehn Sidney Ison Safaa Sader Ivana Ivanovi-Burmazovi Christian R. Goldsmith 《Chemical science》2021,12(31):10483
Reactivity assays previously suggested that two quinol-containing MRI contrast agent sensors for H2O2, [Mn(H2qp1)(MeCN)]2+ and [Mn(H4qp2)Br2], could also catalytically degrade superoxide. Subsequently, [Zn(H2qp1)(OTf)]+ was found to use the redox activity of the H2qp1 ligand to catalyze the conversion of O2˙− to O2 and H2O2, raising the possibility that the organic ligand, rather than the metal, could serve as the redox partner for O2˙− in the manganese chemistry. Here, we use stopped-flow kinetics and cryospray-ionization mass spectrometry (CSI-MS) analysis of the direct reactions between the manganese-containing contrast agents and O2˙− to confirm the activity and elucidate the catalytic mechanism. The obtained data are consistent with the operation of multiple parallel catalytic cycles, with both the quinol groups and manganese cycling through different oxidation states during the reactions with superoxide. The choice of ligand impacts the overall charges of the intermediates and allows us to visualize complementary sets of intermediates within the catalytic cycles using CSI-MS. With the diquinolic H4qp2, we detect Mn(iii)-superoxo intermediates with both reduced and oxidized forms of the ligand, a Mn(iii)-hydroperoxo compound, and what is formally a Mn(iv)-oxo species with the monoquinolate/mono-para-quinone form of H4qp2. With the monoquinolic H2qp1, we observe a Mn(ii)-superoxo ↔ Mn(iii)-peroxo intermediate with the oxidized para-quinone form of the ligand. The observation of these species suggests inner-sphere mechanisms for O2˙− oxidation and reduction that include both the ligand and manganese as redox partners. The higher positive charges of the complexes with the reduced and oxidized forms of H2qp1 compared to those with related forms of H4qp2 result in higher catalytic activity (kcat ∼ 108 M−1 s−1 at pH 7.4) that rivals those of the most active superoxide dismutase (SOD) mimics. The manganese complex with H2qp1 is markedly more stable in water than other highly active non-porphyrin-based and even some Mn(ii) porphyrin-based SOD mimics.Manganese complexes with polydentate quinol-containing ligands are found to catalyze the degradation of superoxide through inner-sphere mechanisms. The redox activity of the ligand stabilizes higher-valent manganese species. 相似文献