Multinuclear compounds of s-elements with sterically hindered <Emphasis Type=Italic>о</Emphasis>-semiquinonates and catecholates

Alkali metals form mutinuclear compounds with redox-active singly and doubly reduced derivatives of sterically of hindered о-benzoquinones. Complexes [Na₆(Cat)₃(THF)₇]?4THF, [Na₅(Cat)₂(SQ)(THF)₅], [Na₄(SQ)₄(THF)₄]?THF?C₆H₁₄, [Na₄(3,5-SQ)₄(THF)₄], [K₄(SQ)₄(THF)₄]?4THF and [Li₃(SQ)₃(THF)₃]?THF (Cat is catecholate, SQ is semiquinonate) possessing high sensitivity to atmospheric oxygen were synthesized and their structures were determined. Magnetochemical measurements and quantum chemical calculations revealed that variation of the alkali metal and/or change in the structure of the polymetallic core significantly affect the energy of exchange interaction between the unpaired electrons of the paramagnetic ligands framing the polynuclear metal core formed by s-elements.     

Frequency spectrum of tantalum at temperatures of 293–2300 K

The temperature dependence of the frequency spectrum of tantalum in the temperature range from room temperature to 2300 K has been studied for the first time using inelastic slow-neutron scattering. The inelastic slow-neutron scattering spectra have been measured at different temperatures on a DIN-2PI time-of-flight spectrometer installed at the IBR-2 nuclear reactor (Joint Institute for Nuclear Research, Dubna, Russia) with the use of a TS3000K high-temperature thermostat. From the measured spectra, the frequency spectra of the tantalum crystal lattice have been determined at temperatures of 293, 1584, and 2300 K by the iteration method. As the temperature increases, the frequency spectrum, on the whole, is softened and the specific features manifested themselves at room temperature are smoothed. The variations observed have been explained by the increase in the role of the effects of vibration anharmonism at high temperatures.     

Electrochemical Reduction and Oxidation of 3,4-Disubstituted 1,2,5-Thiadiazoles

The electron-acceptor nitrogen and sulfur atoms in 3,4-disubstituted 1,2,5-thiadiazoles are responsible for much decreased reduction potentials and much increased oxidation potentials of these compounds compared with the corresponding carbocyclic derivatives. The thiadiazole ring is resistant to oxidation, and the reversible electron transfer gives rise to fairly stable radical cations. Reductive stability of the heterocycle depends on the nature of its substituents and on the medium: When nucleofuge substituents are present, two-electron transfer in aprotic media results in heteroring opening with iminonitrile formation, whereas in the presence of two readily leaving groups, the electron transfer induces cleavage of the complete heteroring into inorganic anions.     

ESR study of structural characteristics and intramolecular motions of tris(3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-4-hydroxybenzyl)amine free radical in toluene

The magnetic and dynamic properties of tris(2,6-di-tert-butyl-4-hydroxybenzyl)amine free radical was studied by ESR spectroscopy in the temperature range from 170 to 350 K in toluene. Symmetrical conformers in the rigid toluene matrix with characteristic angles θ₁ = 26° and θ₂ = 60° between the symmetry axis of the 2p _z -orbital on the C_α atom of the phenoxyl ring and the direction of the C_α-C_β bond of the CH₂ fragment were determined. The activation energy of transition between the conformers was determined to be 8.2 kcal mol⁻¹. The correlation time of transition between the conformers was established as 8.2·10⁻¹ s.     

Molecular-beam mass spectrometry of van der Waals clusters. Mass spectrum of hydrogen sulfide dimer

Hydrogen sulfide clusters generated by ultrasonic expansion of an H₂S-Ar mixture into a vacuum were detected by electron impact mass spectrometry. The mass spectrum of the dimer, (H₂S)₂, was obtained under conditions of predominant dimerization. A mechanism of the formation of ions that involves intracluster reactions between the fragment ions of the monomer and the monomer molecule has been suggested.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 839–844, May, 1995.The work was carried out with the financial support of the Russian Foundation for Basic Research (Project No. 93-03-4933). The authors are also grateful to the European Environmental Research Organisation (EERO) for support.     

ESR study of NiIII complexes with nitrosonaphthols and dithio acids

Mixed-ligand Ni^III complexes with -nitroso--naphthol, -nitroso--naphthol,o-ethylxanthate, andN,N-diethyldithiocarbamate as ligands have been studied by ESR in liquid and frozen solutions. The degrees of symmetry distortion for the first coordination sphere of these complexes have been determined. It is shown that the transition from planar square Ni^IIL₂ complexes to more stable octahedral Ni^IIIL₂L and Ni^IIILL₂ complexes occursvia the radical addition mechanism. A method for trapping short-lived radicals is suggested on the basis of the complex formation scheme.Translted fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1513–1515, August, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-5050)     

Synthesis and structure of copper(II) 3-(3′,5′-Di-<Emphasis Type="Italic">tert</Emphasis>-butyl-4′-hydroxybenzyl)acetylacetonate

Copper(II) 3-(3,5-di-tert-butyl-4-hydroxybenzyl)acetylacetonate was prepared, and its molecular and crystal structure were determined by single crystal X-ray diffraction. There are two crystallographically independent molecules of the complex in the crystal. In the first molecule, the square planar coordination of Cu(II) is virtually ideal, and in the second molecule it is somewhat distorted. On the whole, the conformations of the independent molecules are similar. The ESR spectrum of the polycrystalline complex suggests magnetic coupling of the Cu atoms and magnetic ordering. In solution in coordination-inert toluene, heating increases the contribution of tetrahedral distortions. In ethanol, the solvent molecule additionally coordinates at the axial positions of the complex.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1775–1781.Original Russian Text Copyright © 2004 by Podyachev, Bukharov, Litvinov, Morozov, Gubaidullin, Nugumanova, Mukmeneva.This revised version was published online in April 2005 with a corrected cover date.