A series of nine [Sb7W36O133Ln3M2(OAc)(H2O)8]17? heterometallic anions ( Ln3M2 ; Ln=La–Gd, M=Co; Ln=Ce, M=Ni and Zn) have been obtained by reacting 3 d metal disubstituted Krebs‐type tungstoantimonates(III) with early lanthanides. Their unique tetrameric structure contains a novel {MW9O33} capping unit formed by a planar {MW6O24} fragment to which three {WO2} groups are condensed to form a tungstate skeleton identical to that of a hypothetical trilacunary derivative of the ?‐Keggin cluster. It is shown, for the first time, that classical Anderson–Evans {MW6O24} anions can act as building blocks to construct purely inorganic large frameworks. Unprecedented reactivity in the outer ring of these disk‐shaped species is also revealed. The Ln3M2 anions possess chirality owing to a {Sb4O4} cluster being encapsulated in left‐ or right‐handed orientations. Their ability to self‐associate in blackberry‐type vesicles in solution has been assessed for the Ce3Co2 derivative. 相似文献
A study on the influence of the cation coordination number, number of Lewis acid centers, concurrent existence of Lewis base sites, and structure topology on the catalytic activity of six new indium MOFs, has been carried out for multicomponent reactions (MCRs). The new indium polymeric frameworks, namely [In8(OH)6(popha)6(H2O)4]?3 H2O ( InPF‐16 ), [In(popha)(2,2′‐bipy)]?3 H2O ( InPF‐17 ), [In3(OH)3(popha)2(4,4′‐bipy)]?4 H2O ( InPF‐18 ), [In2(popha)2(4,4′‐bipy)2]?3 H2O ( InPF‐19 ), [In(OH)(Hpopha)]?0.5 (1,7‐phen) ( InPF‐20 ), and [In(popha)(1,10‐phen)]?4 H2O ( InPF‐21 ) (InPF=indium polymeric framework, H3popha=5‐(4‐carboxy‐2‐nitrophenoxy)isophthalic acid, phen=phenanthroline, bipy=bipyridine), have been hydrothermally obtained by using both conventional heating (CH) and microwave (MW) procedures. These indium frameworks show efficient Lewis acid behavior for the solvent‐free cyanosilylation of carbonyl compounds, the one pot Passerini 3‐component (P‐3CR) and the Ugi 4‐component (U‐4CR) reactions. In addition, InPF‐17 was found to be a highly reactive, recyclable, and environmentally benign catalyst, which allows the efficient synthesis of α‐aminoacyl amides. The relationship between the Lewis base/acid active site and the catalytic performance is explained by the 2D seven‐coordinated indium framework of the catalyst InPF‐17 . This study is an attempt to highlight the main structural and synthetic factors that have to be taken into account when planning a new, effective MOF‐based heterogeneous catalyst for multicomponent reactions. 相似文献
It is known that under resonance conditions, a group of strongly interacting bosonic atoms, trapped in a double-well potential, mimics a single particle, performing Rabi oscillations between the wells. By implication, all atoms need to tunnel at roughly the same time, even though the Bose–Hubbard Hamiltonian accounts only for one-atom-at-a-time transfers. The mechanism of this collective behavior is analyzed, the Rabi frequencies in the process are evaluated, and the limitation of this simple picture is discussed. In particular, it is shown that the small rapid oscillations superimposed on the slow Rabi cycle result from splitting the transferred cluster at the sudden onset of tunnelling, and disappear if tunnelling is turned on gradually. 相似文献
In this work, the catalytic activity of carbon nanotubes (CNTs), carbon black (CB), and CNT-CB counter electrodes in the I−/I3− reduction reaction is reported and compared with the Pt counter electrode. The fabricated counter electrodes were evaluated in dye-sensitized solar cells (DSSCs). The results indicate that the best cathodes were made from CNT10 (240 μm) and CB with a charge transfer resistance (RCT) of 2.70 Ω, and when the complete device shows 19.83 Ω of internal series resistance (RS), the photovoltaic parameters of these cells were JSC = 10.47 mA cm−2; VOC = 0.70 V; and FF = 57.90, with an efficiency of 4.29%, indicating a better interaction between the CNT10 in the 3D network of the counter electrode, generating a good charge transfer kinetics, in comparison with only CNT10 or CB.
Anion-π catalysis operates by stabilizing anionic transition states on π-acidic aromatic surfaces. In anion-(π)n-π catalysis, π stacks add polarizability to strengthen interactions. In search of synthetic methods to extend π stacks beyond the limits of foldamers, the self-assembly of micelles from amphiphilic naphthalenediimides (NDIs) is introduced. To interface substrates and catalysts, charge-transfer complexes with dialkoxynaphthalenes (DANs), a classic in supramolecular chemistry, are installed. In π-stacked micelles, the rates of bioinspired ether cyclizations exceed rates on monomers in organic solvents by far. This is particularly impressive considering that anion-π catalysis in water has been elusive so far. Increasing rates with increasing π acidity of the micelles evince operational anion-(π)n-π catalysis. At maximal π acidity, autocatalytic behavior emerges. Dependence on position and order in confined micellar space promises access to emergent properties. Anion-(π)n-π catalytic micelles in water thus expand supramolecular systems catalysis accessible with anion-π interactions with an inspiring topic of general interest and great perspectives. 相似文献
Isothermal retention indices (I) at 333–413 K on 12 stationary phases (SPs) covering a wide polarity range of a variety of volatile solutes belonging to 7 one-heteroatom chemical function series and 10 non-series solutes have been determined. The I values were computed with a method (LQG method) which does not require the determination of holdup times of the chromatographic column. I values of some compounds never before studied are reported. The influence on the retention indices of the column temperature, methylene number, and polarity of both the stationary phase and the solute has been studied. The solvation parameter model (SPM) as a function of I has been used for predicting I values, and for unraveling the influence of the polarity of stationary phase and solute on the retention indices. Seeley et al.’s formulation of the SPM has been used for quantifying the influence of polar and non-polar interactions on the I, and for checking the agreement between calculated and experimental values. According to our results, the I values obtained by the modified SPM can be considered equal to the experimental I values at the 99 % confidence level.