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131.
Synthesis and Characterization of Two Discrete Ln10 Nanoscopic Ladder‐Type Cages: Magnetic Studies Reveal a Significant Cryogenic Magnetocaloric Effect and Slow Magnetic Relaxation
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Two unique lanthanide‐based cages [Ln10( L )5(μ2‐OH)6(H2O)22](Cl)4?7 H2O ([Gd10] and [Dy10]) have been synthesized by using a hydrazone‐based ligand H4 L (H4 L =2,6‐bis[(3‐methoxysalicylidene)hydrazinecarbonyl]pyridine) and LnCl3?x H2O. Structural characterization of [Gd10] reveals an aesthetically pleasing self‐assembly of five L 4? and ten Gd3+ ions forming a 2×[1×5] rectangular array. The ladder‐shaped cage consists of three “rungs” and two “rails” that are occupied by five ligands. Six out of ten gadolinium centers act as rung locks. Further analysis revealed that three chloride ions are encapsulated inside each discrete [Gd10] molecule through hydrogen bonding and other noncovalent interactions. Both the complexes ([Gd10] and [Dy10]) were characterized by powder X‐ray diffraction and thermogravimetric analysis, which shows that they are isostructural in nature. Magnetic investigations reveal that [Gd10] is a good candidate for magnetic refrigeration with a significant entropy change (?ΔSm) of 37.4 J kg?1 K?1 for an applied field of 7 T and at 3 K. Whereas [Dy10] shows single‐molecule‐magnet‐like behavior. 相似文献
132.
Allen Donnelly Swapan Chowdhury Alex. G. Harrison 《Journal of mass spectrometry : JMS》1989,24(2):89-93
The reaction of [OH]? with 2-pentanone produces two enolate ions, [CH3CH2CH2COCH2]? and [CH3COCHCH2CH3]?, by proton abstraction from C(1) and C(3), respectively. Using deuterium isotopic labelling the fragmentation reactions of each enolate have been delineated for collisional activation at both high (8 keV) and low (5–100 eV) collisional energies. The primary enolate ion fragments mainly by elimination of ethene. Two mechanisms operate: elimination of C(4) and C(5) with hydrogen migration from C(5), and elimination of C(3) and C(4) with migration of the C(5) methyl group. Minor fragmentation of the primary enolate also occurs by elimination of propane and elimination of C2H5; the latter reaction involves specifically the terminal ethyl group. The secondary enolate ion fragments mainly by loss of H2 and by elimination of CH4; for the latter reaction four different pathways are operative. Minor elimination of ethene also is observed involving migration of a C(5) hydrogen to C(3) and elimination of C(4) and C(5) as ethene. 相似文献
133.
Through a new local density approximation to the kinetic energy density functional introduced by us recently, a simple Thomas–Fermi-like scheme for the direct calculation of electron density in atoms is proposed. The calculated density is nonsingular at the nucleus and the energy values are in very good agreement with the corresponding Hartree–Fock results for atoms. © 1994 John Wiley & Sons, Inc. 相似文献
134.
The kinetics of the interactions of the Keggin type heteropolyanion [CoW12O40]5?, with all the molecular and anionic forms of citric acid have been investigated spectrophotometrically in the pH range 0.60–5.45 at 60°C. With the exception of the molecular form of the acid (H3L), all the other species (H2L?, HL2?, and L3?) undergo oxidation through an alkali metal ion catalyzed path in addition to the uncatalyzed one. The catalytic power increases with increasing size of the alkali metal ion. The contributions of each path have been evaluated from the kinetic data with the help of the measured dissociation constant values of citric acid. A plausible mechanism involving the formation of a bridged outer-sphere complex of the reacting species with the alkali cation, has been suggested. The observed limiting dependence of kobs on [citrate] at high concentrations owing to an equilibrium between the reactants preceeding the electron transfer step supports the proposed mechanism. The pH-rate profile gives an excellent fit with the evaluated kinetic parameters. 相似文献
135.
The kinetics of the interaction of glycine with cis‐[Pt(en)(H2O)2](ClO4)2 and cis‐[Pt(dmen)(H2O)2](ClO4)2 (en = ethylenediamine, dmen = N,N′‐dimethylethylene‐diamine) have been studied spectrophotometrically as a function of [substrate complex], [glycine], and temperature at a particular pH (4.0) where the substrate complex exists predominantly as the diaqua species and glycine as the zwitterion. The reaction was found to proceed through two consecutive steps. The first step involves the ligand‐assisted anation, while the second step involves chelation when the second aqua ligand is displaced. Rate constants have been evaluated using the Weyh and Hamm method. Activation parameters for both steps have also been calculated using the Eyring equation. The low enthalpy of activation and large negative values of entropy of activation indicate an associative mode of activation for both steps. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 489–495, 2005 相似文献
136.
The kinetics of the interaction of L ‐asparagine with [Pt(ethylenediamine)(H2O)2]2+ have been studied spectrophotometrically as a function of [Pt(ethylenediamine)(H2O)22+], [L ‐asparagine], and temperature at pH 4.0, where the substrate complex exists predominantly as the diaqua species and L ‐asparagine as the zwitterion. The substitution reaction shows two consecutive steps: the first step is the ligand‐assisted anation and the second one is the chelation step. Activation parameters for both the steps have been calculated using Eyring equation. The low ΔH1≠ (43.59 ± 0.96 kJ mol?1) and large negative values of ΔS1≠ (?116.98 ± 2.9 J K?1 mol?1) as well as ΔH2≠ (33.78 ± 0.51 kJ mol?1) and ΔS2≠ (?221.43 ± 1.57 J K?1 mol?1) indicate an associative mode of activation for both the aqua ligand substitution processes. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 252–259, 2003 相似文献
137.
138.
We derive a one-dimensional energy diffusion equation for describing the dynamics of multidimensional electron transfer reactions in condensed phase, which is conceptually simpler and computationally more economic than the conventional approaches. We also obtain an analytical expression for the rate of electron transfer reactions for a general one-dimensional effective potential as well as an energy dependent diffusitivity. As an illustrative example, we consider application to electron transfer in a contact ion pair system modeled through harmonic potentials consisting of two slow classical modes and a high frequency vibrational mode for which the numerical results calculated using the proposed one-dimensional approach are shown to be in good agreement with experimental results. The energy diffusion equation and the rate expression for electron transfer obtained from the present theory, therefore, open up the possibility of describing the dynamics of electron transfer in complex systems, through a simpler approach. 相似文献
139.
Compounds possessing the Kagome network are truly interesting because of their unusual low-energy properties. They exhibit magnetic frustration because of the triangular lattice inherent to the hexagonal bronze structure they possess, as indeed demonstrated by some of the Fe(3+) jarosites, but this is not the general case. Kagome compounds formed by transition metal ions with varying spins exhibit novel magnetic properties, some even showing evidence for magnetic order and absence of frustration. We describe the structure and magnetic properties of this interesting class of materials and attempt to provide an explanation for the variety of properties on the basis of theoretical considerations. 相似文献
140.
We perform density functional calculations on one-dimensional zigzag edge graphene nanoribbons (ZGNRs) of different widths, with and without edge doping including semilocal exchange correlations. Our study reveals that, although the ground state of edge-passivated (with hydrogen) ZGNRs prefers to be anti-ferromagnetic, the doping of both of the edges with boron atoms stabilizes the system in a ferromagnetic ground state. Both the local and semilocal exchange correlations result in half-metallicity in edge-passivated ZGNRs at a finite cross-ribbon electric field. However, the ZGNR with boron edges shows half-metallic behavior irrespective of the ribbon width even in the absence of electric field and this property sustains for any field strength, opening a huge possibility of applications in spintronics. 相似文献