Preparation and properties of the systems Co1−xRhxS2, Co1−xRuxS2, and Rh1−xRuxS2

Members of the systems Co_1−xRh_xS₂ (0 ≤ x ≤ 0.6) were prepared, and their crystallographic and magnetic properties studied. The observed ferromagnetic moments for compositions where x ≤ 0.2 indicate a ferromagnetic alignment between Co(3d⁷) and Rh(4d⁷) electrons. This is the first observation of localized behavior of 4d electrons in the pyrite structure. Members of the systems Co_1−xRu_xS₂ (0 ≤ x ≤ 1) and Rh_1−xRu_xS₂ (0.5 ≤ x ≤ 1) were also prepared and their crystallographic and magnetic properties studied. From comparison with the Co_1−xRh_xS₂ system, it appears that the 4d electrons of Rh(4d⁷) are localized in the presence of Co(3d⁷) but are delocalized in the presence of Ru(4d⁶). The magnetic susceptibility of the Co_1−xRu_xS₂ system is sensitive to the homogeneity of the products and indicates that Ru(4d⁶) behaves as a diamagnetic ion.     

The electronic structure of the SbF2−5 ion and isoelectronic species

The electronic structure of the SbF²⁻₅ion and the isoelectronic species TeF⁻₅, IF₅ and XeF⁺₅ are calculated using the Discrete Variational X_α-method (DVM-X_α). The nature of chemical Bonding is analysed in terms of a Mulliken population scheme. The factors leading to geometrical distortions of the SbF²⁻₅ coordination polyhedron are discussed. The results of calculations cast doubts on the validity of the assumption that the geometry of the anion is influenced by the lone pair.     

Influence of chlorine and potassium additives on the catalytic properties of reduced Mo?Ni and Cr?Ni complex compounds

Chlorine and potassium are introduced during the preparation of Mo–Ni and Cr–Ni complex compounds by using nickel chloride and potassium molybdate or dichromate as starting materials. The resulting compounds are isomorphous with a series of complexes prepared with nickel nitrate and ammonium heptamolybdate or dichromate, previously described. The influence of the presence of chlorine and of potassium on the properties of the catalysts obtained by reduction of these compounds by hydrogen is investigated. Potassium-containing catalysts show a behavior similar to copper based catalysts.

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Mo–Ni Cr–Ni, . , , . , . , , .

     

The structure of the SF6 molecule and the SF 6 − anion excited states

The electronic and geometric structures of the ground state and a number of excited states of the SF₆ molecule and the SF ₆ ^– anion have been calculated by the discrete-variation method of the local density-functionals. The anion was found to possess a number of states stable toward the outer electron detachment, and at least one excited state stable toward dissociation. The adiabatic electron affinity (EA) was determined as 3.46 eV at the highest level of theory. This result is correlated to the high EAs of the isovalent compound SeF₆ and TeF₆; however, it does not agree with the presently accepted experimental estimate of 1.0 ± 0.2 eV for the SF₆EA value. The basic anion configuration is octahedral with a S-F bond length of 1.717 Å. The calculated limit for the highest dissociation channel of the ground state SF ₆ ^– SF ₅ ^– + F is 1.5 eV lower than the minimum of the total energy of the neutral molecule; this is in good agreement with experimental estimates.Institute for Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 641–649, March, 1992.     

Untersuchungen in den Dreistoffen: Cr−W−Si und Mo−W−Si

Zusammenfassung Der Schnitt: Me₃Si (Me=Cr, W bzw. Mo, W) wird an Hand heißgepreßter und in Argon homogenisierter Legierungen untersucht; es läßt sich weder das metastabile W₃Si, noch eine W-reiche Mischphase von diesem Typ beobachten. Cr₃Si nimmt bei 1500°C etwa 20 Mol%, W₃Si auf, während Mo₃Si selbst bei 1900°C praktisch kein W₃Si löst (ev. wenige Mol%). Dagegen bestehen lückenlose Mischreihen zwischen den Me₅Si₃-Phasen mit W₅Si₃-Typ. Die grundsätzliche Aufteilung der Phasenfelder ist damit möglich.Mit 2 Abbildungen     

The structure and properties of Li1−xHxNbO3

The properties of Li_1−xH_xNbO₃ have been studied as a function of x, temperature, and stoichiometry of the LiNbO₃ used for its preparation. X-ray diffraction, thermal analysis measurements, and infrared spectroscopy have been used. The intent of this study was to gain a deeper understanding of the basic properties of this material, which has potential importance as a waveguide material in LiNbO₃ optical devices. An approximate phase diagram was constructed for the stoichiometric LiNbO₃HNbO₃ system. In one concentration range (0.56 ≤ x ≤ 0.75), particularly complex structural behavior was found: depending on x, samples undergo one, two, or three phase transitions with temperature, and the system appears to exhibit critical behavior. Samples made by proton exchange of congruent LiNbO₃ ([Li₂O]_0.486[Nb₂O₅]_0.514) show generally similar structural chemistry, with one exception: a new monoclinic phase, isomorphous with MnF₃, was found for 0.75 ≤ x ≤ 0.77. Possible reasons for the refractive index changes caused by proton exchange are discussed.     

Crystal structure of ternary Laves phases in Co—Mn—Nb,Co—Mn—Ta,Co—Re—Nb,and Co—Re—Ta systems

Ternary Laves phases in the three-component systems Co—Mn—Nb, Co—Mn—Ta, Co—Re—Nb, and Co—Re—Ta at 1200 K were established for the first time and crystallographic parameters of these phases were determined.     

Recent Progress in the Transition-Metal-Catalyzed Activation of Si−Si Bonds To Form C−Si Bonds

Disilanes possessing a Si−Si bond are unique element–element species. Transition-metal-catalyzed activation of the Si−Si bond allows many useful transformations that generate diverse organosilanes. This Minireview highlights impressive developments in this field over the past decade, with an emphasis on the formation of vinyl-, aryl-, and acylsilanes by C(sp²)−Si bond formation as well as the formation of allyl- and alkylsilanes by C(sp³)−Si bond formation.     

Syntheses and Br…π supramolecular interactions in the crystal structure of ipriflavone bromides

Supramolecular forces, including electrostatic in- teraction, hydrogen bond, hydrophobic interaction and aromatic stacking interaction, are the important re- search area in supramolecular chemistry and crystal engineering[1]. Aromatic stacking interaction…     

Syntheses and Br...π supramolecular interactions in the crystal structure of ipriflavone bromides

Two novel compounds, 3,8-dibromo-2-methoxyl-7-isopropoxyisoflavanone (1) and 3,6-dibromo-2-methoxyl-7-isopropoxyisoflavanone (2), are synthesized via bromination reaction of their precursor ipriflavone in methanol. The mixture of 1 and 2 co-crystallizes in ethanol and forms two different crystal shapes, the shape of 1 being block and 2 prism, they can be separated manually. 1 and 2 are characterized by IR, ¹H NMR and single crystal X-ray diffraction. The mechanism of bromination reaction is also discussed. 1 crystallizes in the monoclinic space group P2¹/n with cell parameters a = 1.3569(3) nm, b = 0.6706(2) nm, c = 2.0704(4) nm, β = 97.50(2)°, V = 1.8678(6) nm³, Z = 4, Dc = 1.672 Mg/m³, R = 0.0455, wR = 0.0779, F(000) = 936. 2 crystallizes in the monoclinic space group P 2₁/c with cell parameters a =1.3854(17) nm, b = 1.1215(14) nm, c = 1.3038(17) nm, β = 103.71(2)°, V = 1.968(4) nm³, Z = 4, Dc = 1.587 Mg/m³, R = 0.0306, wR = 0.0619, F(000) = 936. The Br...π interactions, hydrogen bonds, aromatic hydrogen bonds and aromatic stacking interactions exist in the crystal structures of 1 and 2, which lead them into supramolecular compounds with a three-dimensional network structure, respectively. 1 and 2 are the isoflavanone derivatives halogenated at C3 and this kind of isoflavanone halides has not been reported yet.     

Structure and magnetic properties of Ho2Co17−xMx pseudobinary compounds

The homogeneity range of the pseudobinary system Ho₂Co_17−xM_x (M ≡; Ni, Fe, Mn, Cr, V, Ti, Cu, Al) and the dependence of the lattice constants and the Curie temperature on composition were studied. Although Ho₂Co₁₇, Ho₂Ni₁₇ and Ho₂Fe₁₇ have identical crystal structures and similar lattice constants, the homogeneity range for the Th₂Ni₁₇-type compound in the Ho₂Co_17−xNi_x and Ho₂Co_17−xFe_x systems is limited to x < 5. The curves of Curie temperature versus composition have maxima at x values of 1, 3 and 0.9 for the systems Ho₂Co_17−xNi_x, Ho₂Co_17−xFe_x and Ho₂Co_17−xCu_x respectively. This suggests that the effect of nickel, iron and copper on the Co-Co exchange interaction in the cobalt sublattice at low concentrations may be different from that at high concentrations.     

The HfNi and ZrNi systems in the region 65 – 80 at.% Ni

The HfNi and ZrNi systems have been examined in the region 65 – 80 at.% Ni by microscope and X-ray analyses.In the HfNi system the following intermediate phases were observed: Hf₃Ni₇, Hf₈Ni₂₁, HfNi₃(h. t.), HfNi₃(l. t.) and Hf₂Ni₇. Hf₃Ni₇, which is formed peritectically at 1250 ± 20 °C, decomposes eutectoidally at 1016 ± 3 °C into Hf₇Ni₁₀ and HfNi₃(l. t.). Hf₈Ni₂₁ is stable from 1300 ± 20 °C, where it forms peritectically, to 1175 ± 10 °C where it decomposes eutectoidally into Hf₃Ni₇ and HfNi₃(l. t.). HfNi₃(h. t.) is a high temperature phase, forming peritectically at 1350 ± 20 °C and transforming into HfNi₃(l. t.) below 1200 ± 10 °C. Hf₂Ni₇ melts congruently. A eutectic between Hf₇Ni₁₀and Hf₃Ni₇ occurs at 1190 ± 10 °C.In the ZrNi system only one phase forming peritectically exists; this is Zr₈Ni₂₁, which is stable at least down to 800 °C. ZrNi₃ is formed in a reaction between Zr₈Ni₂₁ and Zr₂Ni₇ at 920 ± 10 °C. Crystallographic data for the intermediate phases in the HfNi and ZrNi systems in the region 65–75 at.% Ni are presented.     

Synthesis and crystal structure of β-hexanitrohexaazaisowurtzitane

A polycyclic caged compound with high strain—hexanitrohexaazaisowurtzitane (HNIW)—has been synthesized via a three-step reaction: condensation, hydrogenolysis debenzylation and nitrolysis, starting with benzylamine and glyoxal. HNIW is the most powerful high energy density compound (HEDC) ever tested. β-HNIW possesses a caged structure consisting of two five-membered rings and one six-membered ring with a nitro group attached to each of the six bridging nitrogens. The nitro group lies basically within a plane. The lengths of C—C bonds of β-HNIW range from 0. 156 nm to 0.159 nm, 0.002–0.005 nm longer than the sp³ C-C bond. The β-HNIW’s crystal belongs to orthorhombic system and space groupPca2₁ with parameters:a = 0.9670 (2),b = 1.1616 (2),c = 1.3032 (3) nm;V = 1.4638(5) nm³,Z = 4; D_c = 1.989 g/cm³ and D_m = 1.982 g/cm³. Project supported by the Advanced Research Funds (12060451867) from the Commission of Science and Technology for National Defence.     

Synthesis and crystal structure of β-hexanitrohexaazaisowurtzitane

A polycyclic caged compound with high strain——hexanitrohexaazaisowurtzitane (HNIW)——has been synthesized via a three-step reaction: condensation, hydrogenolysis debenzylation and nitrolysis, starting with benzylmine and glyoxal. HNIW is the most powerful high energy density compound (HEDC) ever tested. β-HNIW possesses a caged structure consisting of two five-membered rings and one six-membered ring with a nitro group attached to each of the six bridging nitrogens. The nitro group lies basically within a plane. The lengths of C--C bonds of β-HNIW range from 0.156 nm to 0.159 nm, 0.002--0.005 nm longer than the sp~3 C-C bond. The β-HNIW's crystal belongs to orthorhombic system and space group Pca2_1 with parameters: a=0.9670 (2), b=1.1616 (2), c=1.3032 (3) nm; V=1.4638(5) nm~3, Z=4; D_c=1.989 g/cm~3 and D_m=1.982 g/cm~3.     

Origin of the doublet at 1360 and 1340 cm−1 in the Raman spectra of tryptophan and related compounds

Raman spectra of indole, skatole, tryptophan and its derivatives including C₄-monodeuterated tryptophan were studied with special attention to the origin of the band around 1350 cm⁻¹. The band is observed as a doublet or triplet depending on the compound and solvent, which was ascribed to Fermi resonance between one fundamental and one or two combination bands of the out-of-plane bending vibrations. Removal of the interaction is seen for C₄D-tryptophan and some solutions of skatole. The assignments of the component vibrations were made based on the shifts in frequencies upon C₄-deuteration. In tryptophan derivatives the doublet (or triplet) peaks exhibit steep changes in relative intensity at the pK_a points of the dissociable groups, which is ascribed as arising from slight frequency shifts of a pK_a-sensitive component vibration. Relations between the relative intensity and environment of indole were obtained and their possible applicability to the analyses of Raman spectra of proteins is suggested.     

Thermodynamics of binary and ternary interactions in the tin(II)/phytate system in aqueous solutions,in the presence of Cl− or F−

An extensive study of the tin(II)/phytate (Phy) system was carried out in NaNO_3(aq), at different ionic strengths (0.10 ⩽ I/mol · L⁻¹ ⩽ 1.00) and temperatures (278.15 ⩽ T/K ⩽ 328.15), by potentiometric and voltammetric techniques. The stability and formation enthalpy changes of six SnH_qPhy species were determined. To better characterise this system, some potentiometric titrations were also carried out in mixed ionic media (NaNO_3(aq) + NaCl_(aq) and NaNO_3(aq) + NaF_(aq)) at total ionic strength I = 1.00 mol · L⁻¹. The formation of some ternary mixed SnH_qPhyCl and SnH_qPhyF species (charges omitted for simplicity) was found. The formation enthalpies of the complex species were calculated, at I = 0.40 mol · L⁻¹ in NaNO_3(aq), by the dependence of stability constants on temperature obtained by potentiometric titrations, in the range 278.15 ⩽ T/K ⩽ 328.15. The complex formation process is endothermic, and the main contribution to tin(II) complexation by phytate is entropic in nature. For example, for the SnPhy species we have, at T = 298.15 K and I = 0.40 mol · L⁻¹ in NaNO_3(aq): ΔH = 57.7 ± 2.8 kJ mol · L⁻¹, ΔG = −99.9 ± 1.7 kJ mol · L⁻¹, and TΔS = 158 ± 3 kJ mol · L⁻¹. The ionic strength dependence of the formation constants of the simple tin(II)/phytate species, was modelled by the Debye–Hückel and the SIT approaches. The sequestering ability of phytate towards tin(II) was evaluated by calculating the pL_0.5 values (i.e., the total ligand concentration necessary to bind 50% of cation present in trace) at different ionic strengths, ionic media, and pH. The sequestering ability increases with increasing the pH, whilst it decreases with increasing the ionic strength (the same behaviour shown by the stability constants). Moreover, taking into account the different sequestering ability of phytate towards tin(II) in the different ionic media, the trend: pL_0.5 = 5.70 (in NaNO_3(aq) + NaF_(aq)) > pL_0.5 = 5.16 (in NaNO_3(aq) + NaCl_(aq)) > pL_0.5 = 4.86 (in NaNO_3(aq)) was observed at pH 8.1 and I = 1.00 mol · L⁻¹. This is due to the presence of a second ligand (Cl⁻ or F⁻) that stabilizes the complex species with the formation of ternary complex species. Some empirical relationships were also found.     

Magnetic structure of Fe−Si−Al films implanted with Al and N ions

Changes in the magnetic structure of Fe–Si–Al films due to Al and N ion implantation were studied by⁵⁷Fe Conversion Electron Mössbauer Spectrometry (CEMS). The peaks of the magnetic sextets due to the crystalline films became broader by implantation with 5×10¹⁶ Al/cm², suggesting the formation of amorphous phases. In the CEM spectrum of one sample with large grains implanted with 1×10¹⁷ Al/cm² a crystalline -Fe phase appeared. N implantation with the same dose did not amorphize the sample but the components with high magnetic hyperfine fields were enhanced.