Crystal structure of potassium 2-thiobarbiturate

The crystal and molecular structure of potassium thiobarbiturate C₄H₃KN₂O₂S (C₄H₄N₂O₂S-2-thiobarbituric acid, H₂TBA) is determined. Crystallographic data for KHTBA are as follows: a = 11.2317(17) Å, b = 3.8687(6) Å, c = 14.557(2) Å, β = 97.448(4)°, V = 627.18(17) ų, space group P2/c, Z = 4. Each potassium ion is linked with four oxygen atoms and two S atoms forming a distorted octahedron. N-H…O and C-H…S hydrogen bonds form a branched three-dimensional network. The structure is also stabilized by the π-π interaction of heterocyclic HTBA^? ions.     

Reduction of the laminar compound of graphite with FeCl3 by hydrogen at high pressure

Conclusions A method is proposed for the reduction of laminar graphite compounds at hydrogen pressure up to 70 kbar, which has a number of significant advantages relative to reported methods. This method may be used to obtain new acceptor LGC.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 450–452, February, 1986.The authors express their gratitude to P. B. Fabrichnyi for assistance in the Moessbauer spectral study of these compounds.     

Esters of 1,4-dihydropyridine-3- and -3,5-carbothiolic acids

Methods for the preparation of esters of 1,4-dihydropyridine-3- and -3,5-carbothiolic acids were developed, and their structure and reactivity were studied. A comparative analysis was made of the spectroscopic characteristics of sulfur-containing esters of the 1,4-dihydropyridine series and their oxygen analogs. More strongly expressed electron-acceptor properties of the COSAlk groupings as compared with alkoxycarbonyl substituents were observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 219–228, February, 1982.     

Superconductivities of high-pressure phases in the metal-hydrogen systems

Abstract

The superconducting properties of the d-metal hydrides rank among the most interesting and less studied of their characteristics. Correct and complete data have only been obtained for one superconducting hydride, the palladium hydride'. The long studies on phases forming in the d-metal-hydrogen system in the well- mastered pressure range up to tens of atmospheres have not exhibited any new superconductors, and the scope of systems which could be of interest from this viewpoint has been mainly exhausted'.     

Electronic structure of Al-Cu-Fe quasicrystals

The electronic structure of the Al-Cu-Fe quasicrystal is calculated by the TB-LMTO-ASA method in reciprocal space. The atomic structure of the quasicrystal is modeled by three approximants with 8, 16, and 40 atoms per unit cell. The following characteristics are calculated: partial densities of states for all components of the alloy, total density of states, and charge redistribution between the alloy components. The calculated densities of states are compared with the experimental data obtained by X-ray photoelectron spectroscopy. Good agreement between the experimental spectrum and the theoretical density of states curve is observed for the approximant with 40 atoms per unit cell. In other cases, the agreement is much worse. The calculated data are used to interpret the fundamental features of the experimental spectrum. The results of calculations show that the charge is transferred from transition metal to aluminum atoms, giving rise to d states of aluminum in the occupied part of the band. Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 3, pp. 525-531, May–June, 2000.     

Amorphization of the quenched high pressure phases in Zn-Sb and Cd-Sb systems

Abstract

Solid state amorphization and crystallization of the quenched high pressure phases (h.p.p.) in Zn-Sb and Cd-Sb systems were studied by scanning calorimetry and dilatometry.     

Thermodynamics of Complexation of 18-Crown-6 with NH4+ Ion in Water-Dioxane Mixtures

The stability constants of 1 : 1 complexes of ammonium ion with 18-crown-6 in water and aqueous dioxane (dioxane weight fraction 0.2, 0.4, 0.6, and 0.8) in the range 283-318 K were determined electrometrically, and the thermodynamic parameters of the complexation were calculated. The stability of the complexes is determined by the enthalpy factor. The contributions from the Gibbs energy of solvation of NH₄ ⁺ ion, 18-crown-6·NH₄ ⁺ complex, and free 18-crown-6 to stabilization of the complex with increasing content of dioxane in the mixed solvent were estimated. The thermodynamics of complexation of ammonium, sodium, and potassium ions with 18-crown-6 in aqueous-organic solvents, such as water-2-propanol, water-acetone, and water-dioxane, were compared considering the effects of reactant solvation. The variations of the conformational component of the Gibbs energy of solvation of 18-crown-6 and the parameters of selective solvation of the reactants were evaluated. The influence of the dielectric permittivity and donor-acceptor properties of mixed aqueous-organic solvents on the Gibbs energy of complexation and solvation of the cations and 18-crown-6 was subjected to correlation analysis.     

1,4-Dihydropyridine-3,5-di-and 2-methyl-4-aryl-5-oxo-4,5-dihydro-1H-indeno[1,2-b]pyridine-3-carbothionic acid ethyl esters

Methods for the synthesis of 1,4-dihydropyridine-3,5-di- and 4-aryl-5-oxo-4,5-dlhydro-1H-indeno[1,2-b]pyridine-3-carbothionic acid ethyl esters were developed. A comparative analysis of the physicochemical characteristics of this series of substances is given.Their reactivities in electrochemical and chemical oxidation reactions were studied. The electrochemical oxidation potentials of the thionic acid esters are found in a lower anodic range as compared with their oxygen analogs. According to the ionization constants, the thionic acid esters of 4,5-dihydroindenopyridines are stronger acids than the carbonyl esters; this is explained by participation of the free 3d orbitals of the sulfur atom in stabilization of the anion.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.2, pp. 210–216, February, 1984.     

Synthesis and properties of cystaminium salts with d-metal acid and tetrahalide anions

The products of the reaction of cystamine dihydrochloride CystaH₂Cl₂ (Cysta is NH₂(CH₂)₂SS(CH₂)₂NH₂) with concentrated mineral acids (HBr, HClO₄) and Zn(II), Co(II), or Cu(II) chlorides in 10 M HCl were synthesized and characterized. The compounds CystaH₂Br₂, CystaH₂(ClO₄)₂, CystaH₂[ZnCl₄], CystaH₂[CoCl₄], and CystaH₂[CuCl₄] were obtained. The purity of the compounds was proved by X-ray diffraction, and the composition was determined from chemical and thermal analysis data. According to IR and Raman spectroscopy, all the compounds contain the cation.