Synthesis, crystal and molecular structures, and steroechemical nonrigidity ofN-(chlorodimethylgermylmethyl)-andN-(bromodimethylgermylmethyl)-N-[(S)-1-phenylethyl]acetamides andN-(chlorodimethylgermylmethyl)-4-phenyl-2-pyrrolidone

RacemicN-(chlorodimethylgermylmethyl)-4-phenyl-2-pyrrolidone and the first optically active amide derivatives containing the asymmetrical carbon atom and the five-coordinate germanium atom,viz.,N-(chlorodimethylgermylmethyl)- andN-(bromodimethylgermyl-methyl)-N-[(S)-1-phenylethyl] acetamides, were synthesized. Their structures were established by X-ray diffraction analysis. The geometric characteristics of the trigonal-bipyramidal valence environment about the germanium atoms are compared with those of analogous enantiomeric silicon compounds and the related five-coordinate germanium compounds. The barriers to permutational isomerization of the title compounds were determined by dynamic¹H NMR spectroscopy. It was found that these barriers are higher than those of the corresponding silicon analogs. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 137–144, January, 2000.     

Reactivity of <Emphasis Type="Italic">N</Emphasis>-(chlorodimethylgermyl)methyl and <Emphasis Type="Italic">N</Emphasis>-(chlorodimethylsilyl)methyl derivatives of lactams and amides toward Grignard reagents

N-[(Chlorodimethylgermyl)methyl]lactams and -amides containing a five-coordinate germanium atom react with Grignard reagents chemoselectively by the Ge-Cl bond to form four-coordinate germanium compounds. The method of competitive reactions was used to establish that respective five-coordinate germanium and silicon compounds are almost equally reactive toward Grignard reagents but much more reactive than model four-coordinate germanium and silicon compounds.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 9, 2004, pp. 1462–1465.Original Russian Text Copyright © 2004 by Bylikin, Shipov, Kramarova, Artamkina, Negrebetskii, Baukov.This revised version was published online in April 2005 with a corrected cover date.     

Electronic transport and magnetic properties of the perovskites La0.8Sr0.2Co1−xFexO3; x ≤ 0.3

Transport and magnetic properties of LaCoO₃-based compounds, doped with 20% Sr and 2.5, 5, 10, 15, 20 and 30% Fe, were investigated by means of magnetization, resistivity and magnetoresistance measurements as well as by ⁵⁷Fe Mössbauer spectroscopy. While the temperature dependence of the dc and ac magnetic susceptibilities reveals the presence of magnetic phase separation accompanied by spin-glass and cluster-glass behavior, the electrical resistivity and magnetoresistance characteristics indicate that the mesoscopic structure of the present compounds is rather well described as consisting of ferromagnetic, metallic grains embedded in an insulating matrix. The effect of the partial Co → Fe substitution on the bulk magnetic and transport properties, as well as on the local state of Co and Fe ions is discussed.     

Silicon—nitrogen bond cleavage in N-(dimethylimidosilylmethyl)imides and dimethyl(lactamomethyl)aminosilanes with BF3 etherate as an alternative route to N-(dimethylf luorosilylmethyl)imides and related compounds

N-(Dimethylfluorosilylmethyl)succinimide (2a) and N-(dimethylfluorosilylmethyl)phthalimide (2b) were synthesized by the Si—N bond cleavage in readily accessible N-(dimethylimidosilylmethyl)imides with BF₃ etherate. Analogously, (O→Si)-chelated 1-(dimethylfluorosilylmethyl)-2-pyrrolidone was prepared from 1-(dimethylmorpholinosilylmethyl)-2-pyrrolidone. X-ray diffraction study demonstrated that the silicon atom in the crystals of 2b is pentacoordinated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 558–561, March, 2006.     

Electronic Specific Heat of Vanadium Compounds at Low Temperatures

Russian Physics Journal - The paper presents the research results of the temperature dependence of molar heat capacity at a constant pressure within the temperature range from 5 to 300 K for...     

Spontaneous near-substrate composition modulation in electrodeposited Fe–Co–Ni alloys

Conventional and reverse depth profile analysis of electrodeposited Fe–Co–Ni alloys was performed by secondary neutral mass spectrometry (SNMS). It was found that the reverse sputtering method gave a much better depth resolution at the vicinity of the substrate. The reverse SNMS spectra showed that the deposition of Fe–Co–Ni alloys starts with the formation of an Fe-rich zone followed by an increase in Co concentration, then the nickel content increases and a steady-state alloy composition is achieved. At high current density, the initial depth pattern reproduces itself twice before the composition becomes stable. It was concluded that the varying depth profile is a consequence of the anomalous nature of the codeposition of the alloy components, the depletion of the electrolyte with respect to the metal salts, and the dependence of the intensity of the hydrogen evolution on the deposit surface composition.     

Synthesis and molecular and crystal structures of mono-and bis-chelate hypercoordinate silicon compounds containing the C,O-chelating 2,2-dimethyl-4-oxo-2,3-dihydro-1,3-oxazin-3-ylmethyl ligand

New mono-and bis-chelate hypercoordinate silicon complexes containing the monoanionic C,O-chelating 2,2-dimethyl-2,3-dihydrobenzo-1,3-oxazin-3-ylmethyl (BonCH₂) ligand were synthesized starting from 2,2-dimethyl-2,3-dihydrobenzo-1,3-oxazin-4-one (1) through its TMS derivative 2. The reactions of compound 2 with the chlorosilylmethylating agents ClCH₂SiMe₂Cl, ClCH₂SiMeCl₂, and (ClCH₂)₂SiCl₂ followed by the transformations of the initially formed chlorosilanes BonCH₂SiMe₂Cl (3), BonCH₂SiMeCl₂ (6), and [(BonCH₂)₂Si(Cl)]⁺Cl⁻ (8), respectively, into the target products afforded neutral monochelates, viz., monofluoride BonCH₂SiMe₂F (5) and difluoride BonCH₂SiMeF₂ (7), and the bis-chelate disiloxane cation-anion complexes {[(BonCH₂)₂Si]₂O}²⁺·Cl⁻·ClHCl⁻ (9) and {[(BonCH₂)₂Si]₂O}²⁺·2TfO⁻ (10). The reaction of ditriflate 10 with boron trifluoride etherate produced fluoride triflate (BonCH₂)₂Si(F)OTf (11). The X-ray diffraction study of compounds 5, 7, 9, 10, and 11, as well as of NH-heterocycle 1 and disiloxane (BonCH₂SiMe₂)₂O (4) studied earlier, demonstrated that the Si atoms in complexes 5, 7, 9, and 10 are pentacoordinate through the formation of an intramolecular O→Si bond. The coordination of silicon in fluoride triflate 11 can be described as 5+1. In disiloxane 4, one of two Si atoms is pentacoordinate. Dinuclear cation-anion complexes 9 and 10 contain the diastereomeric bis-silylium ions {[(BonCH₂)₂Si]₂O}²⁺, which differ in the configuration of the chiral bis-chelate fragments (BonCH₂)₂Si. In complex 9, these fragments have opposite configurations (ΛΔ); in ditriflate 10, the same configurations (ΛΛ). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 446–458, March, 2007.     

Synthesis and Some Chemical Properties of 2,2-Dimethyl-4-R-1-oxa-4-aza-2-sila-5-benzocycloheptanones

One-pot synthesis of 2,2-dimethyl-4-R-1-oxa-4-aza-2-sila-5-benzocycloheptanones (R = Me, CH₂SiMe₂Cl) from the N-methylamide of salicylic acid and salicylamide, respectively, by treatment of these amides with a mixture of hexamethyldisilazane and dimethylchloromethylchlorosilane was developed. The hydrolysis and other nucleophilic substitution reactions of the resultant seven-membered silacyclanes were studied. In the case of the silacyclane with R = Me, hydrolysis leads to the corresponding disiloxane, while the silacyclane with R = CH₂SiMe₂Cl gives either 2,2,6,6-tetramethyl-4-(2-hydroxybenzoyl)-2,6-disilamorpholine or its hydrochloride, depending on the reaction conditions. The chlorine atom was replaced by fluorine in the silacyclane with R = CH₂SiMe₂Cl. The structures of 2,2,6,6-tetramethyl-4-(2-hydroxybenzoyl)-2,6-disilamorpholine and its hydrochloride as well as 2,2-dimethyl-4-R-1-oxa-4-az! a-2-sila-5-benzocycloheptanones (R = CH₂SiMe₂Cl, CH₂SiMe₂F) were confirmed by X-ray diffraction.