Recyclization of 4-oxo-1,3-benzoxazinium perchlorates to 4-substituted 5-(o-hydroxyphenyl)-1,2,4-oxadiazolium salts

Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 280–281, February, 1992.     

Magnetic phase transitions in nanostructures induced by shear stress under high pressure

Magnetic phase transitions of the first and second order were revealed by Mössbauer spectroscopy in nanosystems of - and -ferric oxides and metallic europium subjected to shear stress (240°) under high pressure (20 kbar). For - and -ferric oxide nanoclusters, the Curie (Neel) points decreased to 300 K, whereas for nanostructured europium the Neel point increased from 90 to 100 K. The thermodynamic model of magnetic phase transitions predicting a change in the character of magnetic phase transitions and a decrease (increase) in the critical Neel (Curie) points in nanoclusters was developed. The type of magnetic phase transitions and the change in the critical points were caused by defects in nanoclusters, whose maximum concentration was observed for the clusters with the 20—50 nm size range.     

Mössbauer study of thermal decomposition of the [FeCp(SPh)CO]2 complex and its reaction with the surface of activated silica gel

Thermal decomposition of the [FeCp(SPh)CO]₂ complex and its reaction with the surface of activated silica gel were investigated by Mössbauer spectroscopy. A small amount of a complex with properties similar to ferrocene is separated in the first stage of thermal decomposition (120–130°C). The starting carbonyl complex totally disappears in the second stage (165–210°C), and two compounds are present among the products: a derivative of ferrocene and the final product, an x-ray amorphous, iron-containing structure with an ionic-covalent type of chemical bond (CB) and a 25 and 5 wt. % concentration of oxygen and sulfur, respectively. The Mössbauer parameters of this product and the compound formed in the reaction of [FeCp(SPh)CO]₂ with the surface of activated silica gel at 4.2–300 K are identical. The analysis of the data suggested that both structures are highly disperse clusters of iron oxide with the structure of an inverted spinel with superparamagnetic properties.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 771–778, April, 1991.We would like to thank Yu. B. Kopylovskii for assistance in processing the spectra with the MESLIN program.     

Unusual Recyclization of 2(1-Bromostyryl)-4-oxo-1'3-benzoxazinium Perchlorate into 2'3'4'5-Tetrahydro-1'4-benzoxazepine-4'5-dione

Russian Journal of Organic Chemistry -     

Fibroporous polytetrafluoroethylene modified with iron nanoparticles: Structure and electronic and magnetic properties

A method for synthesizing iron-containing nanocomposite based on fibroporous polytetrafluoroethylene (PTFE) is described. Fibroporous PTFE obtained under the radiation of a CO₂ laser on block PTFE is modified in supercritical carbon dioxide (sc CO₂) to form micro- and nanoporous structures. Porous fluoropolymer is treated with a solution of bis(toluene)iron(0) obtained by metal-vapor synthesis (MVS). The composition and structure of iron-containing fluoropolymer is studied by transmission electron microscopy and X-ray photoelectron and Mössbauer spectroscopy. Fe nanoparticles with an average size of 9 nm, consisting of ～30% FeO and ～70% Fe³⁺, are registered in the sample. Fe⁰ nanoparticles are stabilized in fluoropolymer pores and are coated with nanoparticles of nonstoichiometric iron oxides that have superparamagnetic properties.     

Acylation of 2,4-diaryl-4H-chromenes by the action of acetic anhydride and perchloric acid

4H-Chromenes were found to be acylated at the 3-position by the action of acetic anhydride and perchloric acid. The structure was determined of other reaction products — the indenobenzopyrylium and 2,4-diaryl-1-benzopyrylium salts.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1042–1046, August, 1990.     

Study of selective Fischer-Tropsch catalysts synthesized by the destruction of bimetallic carbonyl complexes on activated γ-Al2O3 support

The bimetallic catalysts obtained by the deposition of a Fe?Co binuclear cluster on the dehydroxylated γ-Al₂O₃ are studied and compared to some other relative systems. These bimetallic catalysts are found to be active and selective in olefin synthesis. This is connected with the formation of Fe?Co contact which is detectable by Mössbauer spectroscopy.     

Magnetic phase transitions in nanoclusters and nanostructures

Theoretical models and experimental data on magnetic phase transitions in magnetic nanoclusters and nanostructures were reviewed. It was shown that nanoclusters measuring from several nanometers to several tens of nanometers possess a critical size (which can be likened to the critical Curie or Neel temperatures). At undercritical cluster sizes the magnetic order in cluster and cluster nanostructure vanishes by first-order magnetic phase transitions (abruptly). In this context, a change-over from the first- to second-order magnetic phase transition, a decrease or increase in the Neel and Curie temperatures, and critical nanocluster size calculations were accomplished for a number of nanoobjects. These include ferric oxides and hydroxides in matrix nanostructures comprised of isolated nanoclusters, as well as in nanostructures including strongly interacting or organized clusters and in nanostructures induced by shear stress under high pressure loading.