Copper(II) complexes with pyrazolyl-substituted nitronyl and imino nitroxides

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.     

Photoluminescence of GeSi/Si(0 0 1) self-assembled islands with dome and hut shape

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.     

Continuous extragradient method for a parametric multicriteria equilibrium programming problem

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.     

Ca6.3Mn3Ga4.4Al1.3O18—A novel complex oxide with 3D tetrahedral framework

A new Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ compound has been prepared by solid state reaction in a dynamic vacuum of 5×10⁻⁶ mbar at 1200 °C. The crystal structure of Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ was studied using X-ray powder diffraction (, SG F432, Z=8, R_I=0.031, R_P=0.068), electron diffraction and high resolution electron microscopy. The Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ structure can be described as a tetrahedral [(Ga_0.59Mn_0.24Al_0.17)₁₅O₃₀]^18.24− framework stabilized with embedded [(Ca_0.9Mn_0.1)₁₄MnO₆]^18.24+ polycations, which consists of an isolated MnO₆ octahedron surrounded by a capped cube of (Ca_0.9Mn_0.1) atoms. The Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ structure is related to the structure of Ca₇Zn₃Al₅O_17.5, 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 Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ crystal structure and the structure of the “fullerenoid” Sr₃₃Bi_24+δAl₄₈O_141+3δ/2 oxide is discussed. Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ 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.     

Chemoselectivity in reactions of esterification

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.     

Binding of Cd2+ to self-assembled bilayers bearing pyridine terminal groups: attenuated total reflection Fourier transform infrared spectroscopic studies

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.     

Projections of convex bodies and the fourier transform

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.