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141.
Eugene V. Tretyakov Svyatoslav E. TolstikovElena V. Gorelik Matvey V. FedinGalina V. Romanenko Artem S. BogomyakovVictor I. Ovcharenko 《Polyhedron》2008
It was established that the reactions of pyrazol-3-yl-substituted nitronyl nitroxide (HL1) and pyrazol-3-yl-substituted imino nitroxide (HL3) with Cu(II) acetate lead to self-assembly of the Cu4(OH)2(OAc)4(DMF)2(L1)2 tetranuclear and Cu2(OAc)2(H2O)2(L3)2 dinuclear complexes, respectively. The reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted nitronyl nitroxide (HL2) gave unexpected solid Cu2(H2O)2(L6)2 · 2DMF, in which L6 is a deprotonated 5-carboxy-pyrazol-3-yl-substituted nitronyl nitroxide, formed as a result of cleavage of an ester bond in the starting HL2. A similar transformation of the paramagnetic ligand was observed in the reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted imino nitroxide (HL4). It led to the formation of Cu2(DMF)2(L7)2, where L7 is deprotonated 2-(5-carboxy-1H-pyrazol-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide. An X-ray diffraction study indicated that in Cu4(OH)2(OAc)4(DMF)2(L1)2 and Cu2(OAc)2(H2O)2(L3)2, the L1 and L3 paramagnetic ligands perform the bridging cyclic tridentate function, while in Cu2(H2O)2(L6)2 · 2DMF and Cu2(DMF)2(L7)2, the paramagnetic L6 and diamagnetic L7 are bridging bicyclic tetradentate ligands. The magnetic behavior of complexes with coordinated nitronyl nitroxide – Cu4(OH)2(OAc)4(DMF)2(L1)2 and Cu2(H2O)2(L6)2 · 2DMF is dictated by the dominant antiferromagnetic exchange interactions, which is confirmed by quantum-chemical data. The magnetic susceptibility of Cu2(OAc)2(H2O)2(L3)2 reflects the competition between the antiferromagnetic and ferromagnetic components, of which the latter is due to electron coupling in the Cu(II) ← N=C–N ? O exchange channels. EPR data confirm the results received from static magnetic measurements for multispin solids. 相似文献
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145.
Alexey V. Novikov Mihail V. Shaleev Dmitry N. Lobanov Artem N. Yablonsky Nikolay V. Vostokov Zaharij F. Krasilnik 《Physica E: Low-dimensional Systems and Nanostructures》2004,23(3-4):416
The photoluminescence spectra of GeSi/Si (0 0 1) self-assembled islands produced by solid source molecular beam epitaxy in a wide range (460–700°C) of growth temperatures were investigated. The results showed a blue shift of the island-related photoluminescence peak with a growth temperature lowering from 600°C to 550°C. The observed blue shift of the island photoluminescence peak is associated with a sharp decrease in the average height of the island, which occurs through a change of its shape from dome to hut as the growth temperature lowers from 600°C to 550°C. 相似文献
146.
We consider a multicriteria equilibrium programming problem including, as special cases, the mathematical programming problem,
the problem of finding a saddle point, the multicriteria problem of finding a Pareto point, the minimization problem with
an equilibrium choice of an admissible set, etc. We suggest a continuous version of the extragradient method with prediction
and analyze its convergence. 相似文献
147.
Artem M. Abakumov Joke Hadermann Marina G. Rozova Gustaaf Van Tendeloo 《Journal of solid state chemistry》2005,178(10):3137-3144
A new Ca6.3Mn3Ga4.4Al1.3O18 compound has been prepared by solid state reaction in a dynamic vacuum of 5×10−6 mbar at 1200 °C. The crystal structure of Ca6.3Mn3Ga4.4Al1.3O18 was studied using X-ray powder diffraction (, SG F432, Z=8, RI=0.031, RP=0.068), electron diffraction and high resolution electron microscopy. The Ca6.3Mn3Ga4.4Al1.3O18 structure can be described as a tetrahedral [(Ga0.59Mn0.24Al0.17)15O30]18.24− framework stabilized with embedded [(Ca0.9Mn0.1)14MnO6]18.24+ polycations, which consists of an isolated MnO6 octahedron surrounded by a capped cube of (Ca0.9Mn0.1) atoms. The Ca6.3Mn3Ga4.4Al1.3O18 structure is related to the structure of Ca7Zn3Al5O17.5, but appears to be significantly disordered due to the presence of two orientations of oxygen tetrahedra around the cationic 0,0,0 and x,x,x () positions in a random way according to the F432 space symmetry. The analogy between the Ca6.3Mn3Ga4.4Al1.3O18 crystal structure and the structure of the “fullerenoid” Sr33Bi24+δAl48O141+3δ/2 oxide is discussed. Ca6.3Mn3Ga4.4Al1.3O18 adopts a Curie-Weiss behavior of χ(T) above with a Weiss temperature and per formula unit. At lower temperatures, the χ(T) deviates from the Curie-Weiss law indicating a strengthening of the ferromagnetic component of the exchange interaction. 相似文献
148.
This review is devoted to the problem of chemoselective formation of ester functions in polyfunctional molecules. The review covers most typical approaches to chemoselective acylation of hydroxy groups in molecules containing an amino, mercapto, or another hydroxy functionality as well as chemoselective esterification of di- and polycarboxylic acids. 相似文献
149.
Burshtain D Wu J Melman A Mandler D Scherson DA 《Langmuir : the ACS journal of surfaces and colloids》2004,20(11):4498-4502
Various aspects of the adsorption of Cd2+ on self-assembled monolayers (SAMs) of 4-heptadecylpyridine (HDpy) and 7-tridecyl-4-methyl-1,10-bipyridine (TMbipy) supported on an octadecylsilane (ODS)-modified Ge prism have been examined both ex situ (dry) and in situ (in the presence of aqueous solutions) using attenuated total reflection Fourier transform infrared spectroscopy. In direct analogy with the behavior found for a variety of genuine pyridine (py) and bipyridine (bipy) metal ion complexes, Cd2+ binding to both SAMs led to shifts in the skeletal vibrational modes of the corresponding uncoordinated ligands in the region 1650-1400 cm(-1), toward higher energies. Analysis of spectra acquired ex situ for HDpy/ODS/Ge and TMbipy/ODS/Ge before and after exposure to 0.1 mM [Cd2+] yielded values for the fraction of uncoordinated py, theta(py(un)), and uncoordinated bipy, theta(bipy(un)), of about 0.5 and about 0.1, respectively. The features attributed to the py(un) groups for spectra collected for HDpy/ODS/Ge in situ and ex situ were found to be virtually identical, making it possible to isolate by graphical means the most prominent band of py(co) centered at about 1615 cm(-l) for HDpy/ODS/Ge collected in situ. The resulting bands for pure py(co) and pyun in situ were then used to deconvolute spectra recorded in situ for HPpy/ODS/Ge in contact with Cd2+containing solutions in the range 10 nM < [Cd2+] < 0.1 mM, from which information regarding the adsorption isotherm was obtained. 相似文献
150.
Alexander?KoldobskyEmail author Dmitry?Ryabogin Artem?Zvavitch 《Israel Journal of Mathematics》2004,139(1):361-380
The Fourier analytic approach to sections of convex bodies has recently been developed and has led to several results, including
a complete analytic solution to the Busemann-Petty problem, characterizations of intersection bodies, extremal sections ofl
p-balls. In this article, we extend this approach to projections of convex bodies and show that the projection counterparts
of the results mentioned above can be proved using similar methods. In particular, we present a Fourier analytic proof of
the recent result of Barthe and Naor on extremal projections ofl
p-balls, and give a Fourier analytic solution to Shephard’s problem, originally solved by Petty and Schneider and asking whether
symmetric convex bodies with smaller hyperplane projections necessarily have smaller volume. The proofs are based on a formula
expressing the volume of hyperplane projections in terms of the Fourier transform of the curvature function. 相似文献