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691.
We report here for the first time a multi-scale study on the concept of spin-crossover compounds, which integrates improved density functionals, a polarizable force field and hybrid QM/MM calculations. This multi-scale setup is applied to the temperature dependence of spin states of a Fe(II) compound with trispyrazolylborate ligands that exhibits spin-crossover. Our study shows a transition temperature of around 290 K, which is in perfect agreement with experimental results. Moreover, based on our data we provide the origin of why spin transition occurs in this iron-compound: it results directly from spin-state changes in the iron-compound that lead to more favourable electrostatic interactions for the high-spin state. 相似文献
692.
Poater J Feixas F Bickelhaupt FM Solà M 《Physical chemistry chemical physics : PCCP》2011,13(46):20673-20681
The π-electrons in benzene, the quintessential aromatic molecule, were previously shown to be distortive, i.e., they prefer localized double bonds alternating with single bonds. It is the σ-electrons that force the double bonds to delocalize, leading to a regular, D(6h) geometry. Herein, we computationally investigate the double-bond localizing or delocalizing propensities of σ- and π-electrons in the archetypal all-metal aromatic cluster Al(4)(2-) and its second- and fourth-period analogs B(4)(2-) and Ga(4)(2-), using Kohn-Sham molecular orbital (MO) theory at BP86/TZ2P in combination with quantitative bond energy decomposition analyses (EDA). We compare the three all-metal aromatic clusters with the structurally related organic species C(4)H(4)(2+), C(4)H(4), and C(4)H(4)(2-). Our analyses reveal that the π-electrons in the group-13 M(4)(2-) molecules have a weak preference for localizing the double bonds. Instead, the σ-electrons enforce the regular D(4h) equilibrium geometry with delocalized double bonds. 相似文献
693.
Casitas A Ioannidis N Mitrikas G Costas M Ribas X 《Dalton transactions (Cambridge, England : 2003)》2011,40(35):8796-8799
Well-defined aryl-Cu(III) species undergo rapid reductive elimination upon reaction with phenolates (PhO(-)), to form aryl-OPh cross-coupling products. Kinetic studies show that the reaction follows a different mechanistic pathway compared to the reaction with phenols. The pH active cyclized pincer-like ligand undergoes an initial amine deprotonation that triggers a faster reactivity at room temperature. A mechanistic proposal for the enhanced reactivity and the role of EPR-detected Cu(II) species will be discussed in detail. 相似文献
694.
Miquel Grau-Sánchez José Luis D?´az-Barrero 《Applied mathematics and computation》2011,217(12):5366-5376
In this paper some families of zero-finding iterative methods for nonlinear equations are presented. The key idea to derive them is to solve an initial value problem applying Runge-Kutta techniques. More explicitly, these methods are used to solve the problem that consists in a differential equation in what appears the inverse function of the one which zero will be computed and the condition given by the value attained by it at the initial approximation. Carrying out this procedure several families of different orders of local convergence are obtained. Furthermore, the efficiency of these families are computed and two new families using like-Newton’s methods that improve the most efficient one are also given. 相似文献
695.
Wouter Heyndrickx Pedro Salvador Patrick Bultinck Miquel Solà Eduard Matito 《Journal of computational chemistry》2011,32(3):386-395
Several definitions of an atom in a molecule (AIM) in three‐dimensional (3D) space, including both fuzzy and disjoint domains, are used to calculate electron sharing indices (ESI) and related electronic aromaticity measures, namely, Iring and multicenter indices (MCI), for a wide set of cyclic planar aromatic and nonaromatic molecules of different ring size. The results obtained using the recent iterative Hirshfeld scheme are compared with those derived from the classical Hirshfeld method and from Bader's quantum theory of atoms in molecules. For bonded atoms, all methods yield ESI values in very good agreement, especially for C–C interactions. In the case of nonbonded interactions, there are relevant deviations, particularly between fuzzy and QTAIM schemes. These discrepancies directly translate into significant differences in the values and the trends of the aromaticity indices. In particular, the chemically expected trends are more consistently found when using disjoint domains. Careful examination of the underlying effects reveals the different reasons why the aromaticity indices investigated give the expected results for binary divisions of 3D space. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011. 相似文献
696.
697.
698.
Josep A. Picas Miquel Punset M. Teresa Baile Enric Martín Antonio Forn 《Surface and interface analysis : SIA》2011,43(10):1346-1353
Hard chrome plating has been used in several different applications in industries that require abrasive sliding wear resistance, such as hydraulic pistons, shafts or bearings. However, the increasing environmental and worker safety pressures on electrolytic hard chrome are leading companies to adopt alternatives. The improvements of the high‐velocity‐oxy‐fuel (HVOF) thermal spray process allow the chromium coating replacement with a comparable or superior surface treatment and are more environmentally friendly. This HVOF process, as a flexible dry‐coating technology, avoids high‐volume waste streams and enables a flexible choice of coating material for each application. The cobalt–chromium‐cemented tungsten carbides are some of the easiest materials to spray and the WC‐10Co‐4Cr coatings have demonstrated superior performance over hard chrome with regard to mechanical and tribological properties. In this work, this coating has been deposited with a Sulzer Metco WokaJet‐400 kerosene fuel spray gun, and the spray conditions have been optimized in order to ensure the best properties of the coatings. The mechanical and tribological properties have been evaluated in coatings sprayed with four deposition conditions that involve different gas flow rates. The most wear‐resistant coating is obtained with those HVOF parameters that prevent decarburization of WC particles and, at the same time, allow an adequate agglomerate melting giving a good intersplat adhesion. The results indicate that HVOF‐sprayed WC‐CoCr coatings are a reliable alternative to electrolytic hard chrome (EHC) in the aeronautical industry to coat landing gear components. In particular, in the dry wear tests, the WC‐CoCr coatings outperform hard chrome coatings in wear resistance. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
699.
Szatyłowicz H Krygowski TM Palusiak M Poater J Solà M 《The Journal of organic chemistry》2011,76(2):550-556
The substituent effect in 4-substituted-1,2-benzoquinone is investigated by means of modeling using B3LYP hybrid functional in conjunction with the 6-311+G(d,p) basis set. The interrelation between different types of substituents, X = NO, NO(2), CN, CHO, H, Me, OMe, OH, NH(2), NHMe and N(Me)(2), and both CO groups has been characterized both qualitatively and then quantitatively by means of several measures of π-electron delocalization (HOMA, MCI, DI, FLU) based on structural and electronic properties of 4-substituted-1,2-benzoquinones chosen for analysis. Results of this analysis clearly show that only the meta-placed CO group is affected by substituents, whereas the para-placed CO group is rather insensitive to substitution. These observations may help to explain diversified chemical properties (including reactivity) of CO centers in o-benzoquinone derivatives. Among others, they may explain differences in proton-accepting properties of carbonyl O atoms, as it is shown for simple models in which carbonyl groups in o-benzoquinone act as proton acceptors in H-bonds of O···H-F type. 相似文献
700.
The recently reported SSB-D functional [J. Chem. Phys. 2009, 131, 094103] is used to check the performance for obtaining nuclear magnetic resonance (NMR) shielding constants. Four different databases were studied, which contain a diversity of molecules and nuclear shielding constants. The SSB-D functional is compared with its "parent" functionals (PBE, OPBE), the KT2 functional that was designed specially for NMR applications and the coupled cluster CCSD(T) method. The best performance for the experimentally most-used elements ((1)H, (13)C) is obtained for the SSB-D and KT2 functionals. 相似文献