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71.
Halogeno Metallates of Transition Elements with Cations of Nitrogen‐containing Heterocyclic Bases. VIII Syntheses and Crystal Structures of Novel Bromoferrates(III), Chloro‐, and Aquachloroferrates(III) with Tetrahedral and Octahedral Iron Coordination, among them two Neutral Complexes of Iron(II) and (III) (dmpipzH2)[FeIIIBr4]2 ( 1 ), (trienH2)[FeIIIBr4]Br ( 2 ), (dmpipzH2)[FeIIICl4]Cl ( 3 ), (dmpipzH2)2[FeIII(H2O)2Cl4][FeIIICl4]Cl2 ( 4 ), and (trienH2)[FeIII(H2O)3Cl3]Cl2 ( 5 ) crystallize from aqueous mineralic acid solutions of iron(II) halide and the organic bases (1,4‐dimethylpiperazine or triethylenediammine) in the presence of atmospheric oxygen whereas (dmpipzH2)[FeCl4(H2O)6]Cl2 ( 6 ) was obtained under the exclusion of air. 1 , 2 , and 3 contain the known tetrahedral halogeno complexes, 4 contains a novel octahedral iron(III) complex, and in 6 a neutral binuclear iron(II) complex has been found which has not been described before. The crystal structures and the hydrogen bridging systems of the complexes are described. 相似文献
72.
Marina M. Lezhnina Edgar Jordan Sergej A. Klimin Jürgen Löns Hubert Koller Boris N. Mavrin Ulrich Kynast Prof. Dr. 《无机化学与普通化学杂志》2009,635(3):450-455
In the course of investigations on optical properties resulting from the interaction of fluorides with alumosilicate host materials and rare earth guests, a well defined BF4– ion wasfound to be incorporated within the sodalite of composition Na8Al6Si6O24(BF4)2. The resulting cubic molecular structure, which was determined by Rietveld methods (space group P4 n, a = 906.91 pm, wRp = 0.045, Rp = 0.027), contains one anion in each sodalite cage and is, contrarily to expectations, thermally stable. NMR spectroscopic investigations indicated a fast rotatory motion of the BF4– tetrahedra at room temperature and agreed with the tetrahedral BF4– ions found in IR and Raman spectra. Preliminary attempts to obtain a luminescent material by incorporation of Eu3+ through aqueous ion exchange only yielded low rare earth concentrations, giving rise to characteristic red emission lines at 581 nm (5D0 → 7F1) and 615 nm (5D0 → 7F2) in a 1:2 intensity ratio. The material unexpectedly exhibited a strong broad band emission at 520 nm after calcination under Ar, which is attributed to the formation of an Eu2+ species. Further calcination under air partially reestablished the Eu3+ emission. 相似文献
73.
Sergej Naumov Marija Bonifačić Richard S. Glass Klaus-Dieter Asmus 《Research on Chemical Intermediates》2009,35(4):479-496
A complementary quantum mechanical and experimental study has been undertaken on the reactivity, formation and properties
of Se∴N and S∴N σ2/σ* three-electron-bonded radical species, generated upon one-electron oxidation of selenomethionine, methionine and structurally
related compounds. The quantum chemical calculations were based on density functional theory (DFT) hybrid B3LYP and BHandHLYP
methods with basis sets ranging from 6-31G(d) to 6-311+G(d,p). Solvent effects, which play an important role concerning structure
and energy of ground and excited states, were taken into account as dielectric continuum as well as explicit water molecules.
They fully confirm new and previously obtained experimental results concerning the Vis/near-UV absorptions and thermodynamic
stability. Special emphasis was put on a comparison between selenium and sulfur. The calculations clearly confirm the higher
thermodynamic stability of the Se∴N radical species relative to the S∴N ones, and also corroborate the observed much higher
kinetic stability of the former. Concerning optical absorptions, the calculations predict the Se∴N transients to exhibit a
blue-shift by about 20 nm relative to the S-based analogues, confirming the few experimental data available so far. The theoretical
study includes a comparison of various calculation levels and the influence of the solvent environment, by comparison with
vacuum. New experimental data within the scope of this study have been obtained on intramolecularly-formed S∴N radical cation moieties, structurally stabilized by a rigid norbornane backbone. The methionine-related
species, with an endo-2-amino, exo-2-carboxyl, and endo-6 methylthio substitution, for example, exhibits almost identical
optical and kinetic stability properties as the corresponding species from free methionine. Its optical absorption depends
on the protonation state of the carboxyl group, with λmax at 410 nm for the carboxylate (zwitterionic) form and at 390 nm for the overall cationic form with the protonated carboxyl
group. The fast exponential decays with t
1/2 of 490 ns and 2 μs pertain to the decarboxylation of the respective species. A much longer-lived S∴N species with t
1/2 > 500 μs and second order decay kinetics (λmax 465 nm) was obtained from an endo-2-cyclohexylamino norbornane analogue which does not carry a carboxyl group. The methionine-based
S∴N species is not stable anymore in vacuum and in low polarity solvents. This is explained by a decrease in stabilization
energy of the 3-e-bond and a faster electron transfer from the carboxylate into the cationic 3-e-center. In conclusion, selenium
enhances the thermodynamic and kinetic stability of its radical transients, relative to the sulfur analogues. 相似文献
74.
We consider incremental problem arising in elasto-plastic models with isotropic hardening. Our goal is to derive computable
and guaranteed bounds of the difference between the exact solution and any function in the admissible (energy) class of the
problem considered. Such estimates are obtained by an advanced version of the variational approach earlier used for linear
boundary-value problems and nonlinear variational problems with convex functionals [24, 30]. They do no contain mesh-dependent
constants and are valid for any conforming approximations regardless of the method used for their derivation. It is shown
that the structure of error majorant reflects properties of the exact solution so that the majorant vanishes only if an approximate
solution coincides with the exact one. Moreover, it possesses necessary continuity properties, so that any sequence of approximations
converging to the exact solution in the energy space generates a sequence of positive numbers (explicitly computable by the
majorant functional) that tends to zero.
相似文献
75.
76.
Daniel Leykam Joshua D. Bodyfelt Anton S. Desyatnikov Sergej Flach 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(1):1
Certain tight binding lattices host macroscopically degenerate flat spectral bands. Their origin is rooted in local symmetries of the lattice, with destructive interference leading to the existence of compact localized eigenstates. We study the robustness of this localization to disorder in different classes of flat band lattices in one and two dimensions. Depending on the flat band class, the flat band states can either be robust, preserving their strong localization for weak disorder W, or they are destroyed and acquire large localization lengths ξ that diverge with a variety of unconventional exponents ν, ξ ~ 1 /W ν . 相似文献
77.
Ha X. Nguyen Elena Teidelt Valentin L. Popov Sergej Fatikow 《Archive of Applied Mechanics (Ingenieur Archiv)》2016,86(10):1771-1785
In this paper, the dynamics of piezo-actuated stick–slip micro-drives are studied experimentally and theoretically. First, the stick–slip-based force-generating test stand is introduced, and experimental results are presented. Then, a numerical model is formulated which explicitly includes the dynamics of normal and tangential properties of the contact areas in the frictional driving elements of the drive. The contact forces are simulated using the method of dimensionality reduction. We show that the experimentally observed behavior can be described without using any fitting parameters or assuming any generalized laws of friction if the explicit contact mechanics of the frictional contacts is taken into account. Furthermore, an even simpler model of the drive is developed to get a qualitative understanding of the system. It is employed to gain a new actuation method, which reduces the vibrations of the drive’s runner and therefore enhances its performance. 相似文献
78.
Isabelle Faus Sergej Rackwitz Juliusz A. Wolny Markus Schmitz Harald Kelm Hans-Jörg Krüger Kai Schlage Hans-Christian Wille Volker Schünemann 《Hyperfine Interactions》2014,226(1-3):211-216
The vibrational properties of the (high-spin)-(high-spin) and the (high-spin)- (low-spin) states of the dinuclear Fe(II) spin crossover complex[{Fe(L-N4Me2)}2(BiBzIm)](ClO4)2·2EtCN1 have been studied by means of nuclear inelastic scattering. At a temperature of 80 K typical low spin marker bands are detected in the region around 400 cm?1, these bands almost completely disappear after increasing temperature to 190 K. Corresponding density functional theory calculations using the functional B3LYP* and the basis set CEP-31G reproduce the experimental data and thus allow a deeper understanding of the vibrational properties of dinuclear Fe(II) spin crossover complexes. 相似文献
79.
80.
Medjanik K Chercka D Nagel P Merz M Schuppler S Baumgarten M Müllen K Nepijko SA Elmers HJ Schönhense G Jeschke HO Valenti R 《Journal of the American Chemical Society》2012,134(10):4694-4699
It is demonstrated that the near-edge X-ray absorption fine structure (NEXAFS) provides a powerful local probe of functional groups in novel charge transfer (CT) compounds and their electronic properties. Microcrystals of tetra-/hexamethoxypyrene as donors with the strong acceptor tetracyano-p-quinodimethane (TMP/HMP-TCNQ) were grown by vapor diffusion. The oxygen and nitrogen K-edge spectra are spectroscopic fingerprints of the functional groups in the donor and acceptor moieties, respectively. The orbital selectivity of the NEXAFS pre-edge resonances allows us to precisely elucidate the participation of specific orbitals in the charge transfer process. Upon complex formation, the intensities of several resonances change substantially and a new resonance occurs in the oxygen K-edge spectrum. This gives evidence of a corresponding change of hybridization of specific orbitals in the functional groups of the donor (those derived from the frontier orbitals 2e and 6a(1) of the isolated methoxy group) and acceptor (orbitals b(3g), a(u), b(1g), and b(2u), all located at the cyano group) with π*-orbitals of the ring systems. Along with this intensity effect, the resonance positions associated with the oxygen K-edge (donor) and nitrogen K-edge (acceptor) shift to higher and lower photon energies in the complex, respectively. A calculation based on density functional theory qualitatively explains the experimental results. NEXAFS measurements shine light on the action of the functional groups and elucidate charge transfer on a submolecular level. 相似文献