Exchange interactions and spin dynamics in a [CuNd2(C4O4)4(H2O)16]·2H2O crystal

Crystalline [CuNd₂(C₄O₄)₄(H₂O)₁₆]·2H₂O constructed of complexes of trivalent neodymium and divalent copper, has been synthesized and studied by EPR. The square anion groups (C₄O₄) enter as bridge ligands, forming chains of neodymium ions interconnected by (C₄O₄)Cu(C₄O₄) fragments. It is found that the relaxation rate of the neodymium subsystem at room temperature significantly exceeds the exchange interaction rate between copper and neodymium ions. Under these conditions the magnetic properties of the crystal are determined by two magnetically nonequivalent chains of copper ions, which do not interact. The intrachain exchange interaction via hydrogen bonds is estimated to be ∼0.1 cm⁻¹. As one proceeds from the high-temperature (250<T<300 K) to the low-temperature region (T<40 K), a substantial change in the nature of the interaction is revealed. An unusual magnetic structure given in a crystal is observed at low temperatures, which is determined by the presence of two magnetically nonequivalent “ribbons,” formed by the interacting copper and neodymium ions: chains of copper ions are framed on two sides by chains of neodymium ions. The magnitude of the parameter of the exchange interaction between the copper and neodymium ions is estimated as J ^Cu-Nd⩾0.2 cm⁻¹. An exchange interaction between magnetically nonequivalent neodymium ions is not revealed in the EPR spectra. Fiz. Tverd. Tela (St. Petersburg) 39, 2057–2061 (November 1997)     

Microphase separation and magnetic Jahn-Teller polarons in LaSrAl1−xCuxO4−δ

An EPR study of the solid solutions LaSrAl_1−x Cu_xO₄, which are isostructural to La₂CuO₄, shows that microphase separation of the structure occurs already at small copper concentrations (x≈0.01). A phase enriched with Cu appears along with a phase of La₂AlO₄, which contains isolated CuO₆ centers. It is established that the nature of the states and the deformations of the CuO₆ centers is determined by internal Jahn-Teller factors. When x⩽0.1, EPR signals are detected for new dynamic centers, which are identified as CuO₆ Jahn-Teller centers with a hole delocalized among the four in-plane oxygen ions (the total spin S=1). When 0.1⩽x<1, local CuO ₆ ⁻ hole centers transform into magnetic Jahn-Teller polarons, which include five or more CuO₆ fragments, in the copper phase of the structure. Their transformations and the conditions for observing them are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 622–628 (April 1998)     

Synthesis and antiviral properties of new derivatives of 2-(alkylsulfanyl)-6-[1-(2,6-difluorophenyl)cyclopropyl]-5-methylpyrimidin-4(3<Emphasis Type="Italic">H</Emphasis>)-one

Based on 2-(2,6-difluorophenyl)acetonitrile a synthesis was performed of new bioisosteric prochiral analogs of anti-HIV-1 active derivatives of 2-alkoxy-6-benzylpyrimidin-4(3Н)-one that we had previously obtained. The study using infected and nonifected strains of cells MT-4 made it possible to find in all prepared compounds a high anti-HIV activity whereas the cytotoxicity of the substances depended strongly on the structure of the alkylsulfanyl fragment of the molecule.     

Features of Joint Thermolysis of Organometallic Compounds of Group III and V Elements

The kinetic data on thermolysis of equimolar gaseous mixtures of organometallic compounds of Group III and V elements show that the thermal stability of the mixture differs from that of the components taken separately, which is mainly due to complexation between the mixture components. The complex is a kinetically active species. The rate of joint thermolysis of the organometallic compounds grows as the number of hydride atoms at the Group V element increases in the order AsMe3 < t-BuPH₂ < AsH₃. The stability of the complexes formed by organometallic compounds of Group III and V elements decreases in the same order. Joint thermolysis of Me₃Ga and AsH₃ yields a solid oligomer Me₂GaAs(H)Ga(Me)AsH₂. The complicated pattern of decomposition of a mixture of trimethylaluminum with various electron donors is due to participation in the pyrolysis of two trimethylaluminum species: monomeric and dimeric. In decomposition of pure trimethylaluminum or its mixtures with organometallic compounds of Group V elements or with ether, solid pyrolysis products deposited on the vessel walls catalyzed further transformations of the mixture components.     

Effect of direct-current discharge treatment on the surface properties of chitosan-poly(L,L-lactide)-gelatin composite films

The surface of films made from a chitosan-poly(L,L-lactide)-gelatin mixture stabilized with a grafted-copolymer fraction has been modified by dc discharge treatment, as well as that of films made of the individual components. The surface properties of the films (wettability, surface energy), the chemical structure of surface layers, and their morphology have been examined by goniometric measurement of contact angles, X-ray photoelectron spectroscopy, and scanning electron microscopy.     

Kinetics of solid phase thermal polycondensation of aspartic acid in evacuated system

Solid phase thermal polycondensation of aspartic acid in evacuated system results in formation of poly(aspartic acid) at 190–207°C and in poly(succinimide) at 210–230°C. Kinetic parameters of formation of poly(aspartic acid) and poly(succinimide) have been determined. The aspartic acid → poly(aspartic acid) → poly(succinimide) polycondensation is accompanied by partial decarboxylation of the monomeric units.     

Modification of carbon nano-objects in low-temperature plasma for use in polymer nanocomposites

Literature on the modification of carbon nanotubes and nanofibers in a low-temperature plasma has been surveyed. Basic techniques for the treatment of nano-objects in discharges of various types and various devices used in these processes have been described. Instrumental methods for the investigation of plasma-modified carbon nanotubes and nanofibers and the properties of composites prepared from them with different polymer matrices have been discussed.     

Pressure-controlled plasticity of Cu(H2O)6(2+) complex and phase transition in Cs2Cu(ZrF6)2*6H2O

The X-band EPR study of a polycrystalline Cs2Cu(ZrF6)2*6H2O demonstrates a feature of plasticity of the Jahn-Teller Cu(H2O)6 complex in the crystal lattice of this compound. The temperature- and pressure-induced evolution of the spectra shows that the copper complex is extremely sensitive to these factors, which due to the ferroelastic properties of the compound studied modify the internal tetragonal and orthorhombic strains acting on the complex. It is supported by the analysis of the temperature dependencies of the principal values of the g-factor under various pressures, indicating that the complex varies its shape adapting it to the varied conditions. A pressure-induced phase transition is discovered.     

Reactions of compounds containing SnLi and GeLi bonds with organic and organometallic peroxides

The reactions of tris(trimethylsilylmethyl)stannyllithium, tris(trimethylsilylmethyl)germyllithium and triethylgermyllithium with di-t-butyl peroxide, bis(trimethylsilyl)peroxide, trimethyl(t-butylperoxy)silane, triphenyl(t-butyl-peroxy)germane, bis(triphenylgermyl) peroxide, triphenyl(trimethylsilylperoxy)-germane, benzoyl peroxide and dicyclohexyl peroxydicarbonate were investigated. The reactions proceed under mild conditions with nucleophilic attack by the R₃M anion (R = Et, Me₃SiCH₂, M = Ge, Sn) on one of the peroxide oxygen atoms. In the case of unsymmetrical organometallic peroxides the character of nucleophilic cleavage is dependent on the nature of the starting nucleophile, steric effects of peroxide group substituents and other factors.