A. I. Prokof’ev

Electron paramagnetic resonance and quantum-mechanical analysis of binuclear niobium clusters in lithium–niobium phosphate glasses

Electron paramagnetic resonance (EPR) spectra of Nb4+ ions in Li2O–Nb2O5–P2O5 glasses with different composition of oxide components have been investigated. The EPR spectrum shape analysis of Nb4+ (electron configuration 4d1, electron spin S=1/2) reveals the formation of triplet niobium binuclear complex (total electron spin S=1) in glasses. The amount of Nb4+ ions in glasses reversibly changes with temperature and is explained via the mechanism of electron hopping between niobium ions in clusters. The dependence of the amount of Nb4+ ions upon Li2O content has a maximal character, which implies that small amounts of Li+ ions stabilize the Nb4+ pairs, but cause their disproportionation at higher concentrations of Li+ ions in the glass. Quantum mechanical analysis of electronic and spin states of binuclear niobium clusters has been performed on model binuclear complexes, (HO)3Nb–O–Nb(OH)3, [(HO)3Nb–O–Nb(OH)3]Li+, and [(HO)3Nb–O–Nb(OH)3](Li+)2 that exhibit the reversible disproportionation reaction Nb4+–O–N...

Mechanochemical synthesis of Co, Ni, Fe nanoparticles in polymer matrices

We report on synthesis of Co, Ni, and Fe nanoparticles by the action of elastic wave pulses on solid phase sandwich type samples containing metal salt, reducing agent, polyethylene, and polyacrylamide. The formation of metal nanoparticles is evidenced by ferromagnetic resonance and scanning electron microscopy. The product yield for the nanoparticles formation has a threshold character with the pressure in the elastic wave pulse. The maximum amount of Co, Ni, and Fe nanoparticles is observed around 20 kbar of pressure in elastic wave pulses. The presence of polyacrylamide in reaction composites increases the stability of metal nanoparticles to oxidation by two orders of magnitude.

Magnetism and electronic structure of binuclear manganese complexes in ortho-quinone ligand and polymer environments

By means of mechanochemical synthesis we obtained a coordination polymer containing binuclear manganese complexes with organic catechol∕ortho-quinone ligands. The reaction system contained polystyrene, manganese acetylacetonate, and donor-acceptor mixture catechol∕ortho-quinone. Electron paramagnetic resonance (EPR) and infrared spectroscopic data show that the binuclear manganese complex is covalently linked to the chain of polystyrene. Theoretical EPR spectrum analysis revealed a triplet state of the complex with two nonequivalent manganese ions coupled to each other by spin exchange. The type of magnetic coupling between manganese ions in this system is similar to the one in manganese based inorganic magnetic materials.

Magnetic transitions in manganese benzoquinone coordination polymers

Coordination polymers exhibiting magnetic properties can be considered as promising materials for magnetic applications. We obtained such materials by means pf mechanochemical incorporation of binuclear metal complexes Mn–O–Mn into polystyrene. Incorporation of binuclear manganese complexes was achieved by using substituted benzoquinones (organic acceptors) as intermediate ligands that react with manganese acetylacetonate and provide new coordination and stabilization of manganese in different valence states. Magnetic transitions in this system are due to reversible disproportionation process Mn3+–O–Mn3+⇔Mn2+–O–Mn4+ in the binuclear complex. The structure of the binuclear complex was obtained using ab initio calculations.

Paramagnetic properties of covalently linked mixed valence chromium complexes in polymers

Chromium complexes, where ortho-quinone ligands are covalently linked to polymeric chains of polyethylene, polystyrene, and copolymer of ethylene and vinylacetate are studied. The results of infrared and electron paramagnetic resonance spectroscopic studies of chromium coordination polymers show that covalent linking of quinone ligands is accompanied by the change in the valence states of chromium Cr(III)↔Cr(IV)↔Cr(V). The ligand field of the triplet Cr4+ ion is close to the one in Cr-doped Y2SiO5, a laser material in the visible and infrared regions. Therefore some useful magnetic and/or optical properties in such transition metal coordination polymers can be expected.

Radical cation of hydrogen sulfide and reactions of cyclization of 1,5-Diketones with its participation

Radical cation of hydrogen sulfide is generated electrochemically by γ-irradiating a Freon matrix, under the action of single-electron oxidants (sterically hinderedo-benzoquinones). It is shown that the radical cation exhibits properties of a superacid. The possibility of obtaining thiopyrans and salts of thiopyrilium from substituted 1,5-diketones during an anodic oxidation of molecular hydrogen sulfide to radical cation in acetonitrile is studied.

Radio-frequency superradiance induced by the rheological explosion of polymer composites containing paramagnetic cobalt complexes

Superradiance induced by the rheological explosion of composites based on polystyrene, cobalt acetylacetonate, and/or 3,5-di-tert-butylcatechol has been investigated. The superradiance intensity is determined by solid-phase chemical reactions induced by the rheological explosion. EPR, X-ray diffraction, and electron microscopic characterization of stable products resulting from the rheological explosion in the polymer matrix has demonstrated that the superradiance intensity is related to the electronic properties and structure of two-spin intermediates, namely, radical pairs and organoelement biradicals.

Radio-frequency superradiance at the rheological explosion of a paramagnetic polymer composite containing manganese complexes

It has been revealed that the rheological explosion of a paramagnetic composite (manganese (III) polystyrene acetylacetonate—spatially complicated phenol) is accompanied by the generation of radio-frequency superradiance owing to the annihilation of triplet manganese complexes, as well as by the generation of current pulses.

Radiofrequency superradiance under the rheological explosion of paramagnetic polymer composition

147 Explosive mechanical instability of solids under uniaxial compression accompanied by strong elastic wave pulses was observed for the first time by Bridg man [1]. It has been later shown that propagation of elastic waves in solids occurs simultaneously with charge density transfer, electromagnetic radiation emission [2, 3], and fast solid phase chemical reac tions that cannot be described using classical concepts of thermal activation [4]. In the literature, this phe nomenon is referred to as rheological explosion (RE). The question arises as to whether the RE of a para magnetic polymer composite can result in an ensem ble of inverted molecules, which enables the conver sion of the chemical reaction energy to coherent elec tromagnetic radiation, as well as to a high power electric current pulse. In this work, we used polystyrene based compos ites containing paramagnetic cobalt complexes with 3,5 di tert butyl o benzoquinone ligands (HQ). These composites were selected since the HQ–M–QH com plexes (M is a transition metal) are built into polysty rene chains and fixed by benzene rings like in metal locene structures. This makes it possible to introduce a considerable number of complexes into a polysty rene matrix [5]. Polystyrene–HQ–Co–QH complex systems were prepared. The samples contained the following amounts of cobalt complexes: 0.2 × 1020, 0.4 × 1020, 0.6 × 1020, 0.8 × 1020, 1.0 × 1020, and 1.2 × 1020 in 1 cm3 of the composite. To study fast physicochemical processes at the stage of material failure during rapid uniaxial loading, we used a special high pressure cell, which was placed into an IS 500 compression machine (Fig. 1.). The cell consisted of a Bridgman anvil (1) and a steel car tridge with holes (3) for extraction of electromagnetic radiation (EMR). The sample under study was placed between dies (5). The dies and an EMR sensor (4) consisting of a 0.1 μH inductor and 30 pF capac itor) were connected to a Tektronix MSO200g two channel digital oscilloscope (8). The loading rate was the same (0.5 GPa/s) for all the samples.

A biocompatible nanocomposite based on allyl chitosan and vinyltriethoxysilane for tissue engineering

The synthesis, structure, and electrophysical properties of a polymer-inorganic biocompatible composite based on unsaturated chitosan ether, namely, allyl chitosan, and vinyltriethoxysilane are studied. During composite synthesis, allyl chitosan forms an individual nanophase with vinyltriethoxysilane and its condensation products in the polymer matrix of allyl chitosan. The size of nanoparticles embedded in a polymer matrix increases from 50 to 1000 nm as the fraction of the added vinyltriethoxysilane grows. Under exposure to UV radiation, both homopolycondensation and heteropolycondensation occur in the composite films via crosslinking according to the radical mechanism and the composite becomes insoluble in water. It has been shown that the resulting composites feature ionic conductivity under application of both direct current and high-frequency electric fields to the sample. Conductivity is provided by a proton–electron ensemble that concentrates at the nanoparticle/polymer matrix interface.