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.     

Halogenation of the Hexaphosphabenzene Complex [(Cp*Mo)2(μ,η6:η6-P6)]: Snapshots on the Reaction Progress

The oxidation of [(Cp*Mo)₂(μ,η⁶:η⁶-P₆)] ( 1 ) with halogens or halogen sources was investigated. The iodination afforded the ionic complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ,η¹:η¹:η¹:η¹-P₃I₃)][X] (X=I₃⁻, I⁻) ( 2 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PI₂)][I₃] ( 3 ), while the reaction with PBr₅ led to the complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-Br)₂][Cp*MoBr₄] ( 4 ) [(Cp*MoBr)₂(μ,η³:η³-P₃)(μ,η¹-P₂Br₃)] ( 5 ) and [(Cp*Mo)₂(μ-PBr₂)(μ-PHBr)(μ-Br)₂] ( 6 ). The reaction of 1 with the far stronger oxidizing agent PCl₅ was followed via time- and temperature-dependent ³¹P{¹H} NMR spectroscopy. One of the first intermediates detected at 193 K was [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-PCl₂)₂][PCl₆] ( 8 ) which rearranges upon warming to [(Cp*Mo)₂(μ-PCl₂)₂(μ-Cl)₂] ( 9 ), [(Cp*MoCl)₂(μ,η³:η³-P₃)(μ-PCl₂)] ( 10 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PCl₂)][Cp*MoCl₄] ( 11 ), which could be isolated at room temperature. All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy and their electronic structures were elucidated by DFT calculations.     

Electron Transfer Reaction between M-C_6H_6 and M~ -C_6H_6 Complexes in the Gas Phase: Density Functional Theory Study

Significant progress has been made in understanding the nature of the transition state andthe paths for electron transfer, especially the influences of environmental factors and themolecular properties on the electron transfer rate. These classical and semi-classical, aswell as quantum-mechanical theory, have been very successful in rationalizing severalstructure-reactivity relationships and in predicting novel features of reactivity. Thesemodels established some links between the electron tra…     

Studies on the Reaction of Substituted 6-Nitrocoumarin with Anilines

Greatat'tentionhasbeenpaidtocoumarinsfortheirmulti-activityagainstseveraldiseasessuchascancer,AIDS.Inordertoobtainsomemoreeffectiveanti-tumorcompounds,wedesignedaseriesofcoumarinderivativeswithanovelretinoidsstructure.WhenweattemptedtosynthesisaSchiffbaseofnitrosubstituted3-acetylcoumarins,however,itissurprisinglyfoundthatanewreactionoccurredandasmallersizedSchiffbasewasobtained.'H-NMR,"C-NMR,MSandelementalanalysisshowedthatthenewcompoundwasaheterocyclicringfissionproductI(Schemel).Othe…     

Effect of the Composition of the Water–Dimethyl Sulfoxide Solvent on the Thermodynamics of the Formation of the [Ag(18-Crown-6)]+Complex

The effect of a water–dimethyl sulfoxide solvent (X _DMSO= 0–0.97, where X _DMSOis the mole fraction of DMSO) on the thermodynamics of complexation between Ag⁺and 18-crown-6 and the solvation of all reagents involved in this equilibrium were studied. In aqueous solutions, the complex is stable mainly because of the enthalpy contribution to _r G°. For X _DMSO> 0.3, the contributions from entropy and enthalpy become comparable in magnitude, but they are opposite in sign. In the binary solvent, the complex is most stable at X _DMSO= 0.2 to 0.3. Analysis of the enthalpy characteristics of reagent solvation showed that this solvent effect was due to the superposition of two opposite solvation contributions occurring with an increase in the DMSO concentration in the binary solvent, namely, the destabilization of the ligand solvate sphere and the formation of stable Ag⁺complexes with DMSO.     

Thermogravimetric analysis of the copper silicate mineral dioptase Cu6[Si6O18]·6H2O

There have been a few studies on the thermal decomposition of dioptase Cu₆[Si₆O₁₈]·6H₂O. The results of these analyses are somewhat conflicting and the conclusions vary among these thermo-analytical studies. The objective of this research is to report the thermal analysis of dioptase from different origins and to show the mechanism of decomposition. Thermal decomposition occurs over a very wide temperature range from around 400 to 730 °C with the loss of water. Two additional mass loss steps are observed at around 793 and 835 °C with loss of oxygen. The infrared spectra of dioptase in the hydroxyl stretching region enables the hydrogen bond distances of water molecules in the dioptase structure to be calculated. The large variation in the hydrogen bond distances offers an explanation as to why the decomposition of dioptase with loss of water occurs over such a wide temperature range.     

New Nb6Cl15 − xFx chlorofluoride: Stabilization of the Ta6Cl15 structure-type for binary Nb6 halide

The replacement of a small amount of chlorine by fluorine has made it possible to synthesize Nb₆Cl_{15 − x}F_xin chlorofluoride with the Ta₆Cl₁₅ structure-type. The crystal structures of two compositions in the solid solution (x = 2.2 (I) and x = 4.4 (II)) have been determined by single crystal X-ray diffraction and by isotypy with Ta₆Cl₁₅ (cubic, Ia-3d n° 230, a = 20.099(1) Å, V = 8119.2(1) ų, Z = 16, R = 0.047, R_w = 0.054 for (I) and a = 19.970(2) Å, V = 7964.3(8) ų, Z = 16, R = 0.067, R_w = 0.067 for (II). The structure is based on Nb₆L₁₂ⁱL_6/2^a-a (L = ligand) units in which F is randomly distributed on the inner positions for (I) and (II), and additionally on the apical-apical ones for (II). The unit-cell contains 16 units connected in the 3 directions by bent Nb-L^a-a-Nb bridges. This structure is different from the one encountered for Nb₆F₁₅ which exhibits 2 independent interpenetrating networks with linear Nb-F^a-a-Nb bridges. The interatomic distances obtained from structural data are discussed by comparison with the binary Ta₆Cl₁₅ and isotypic NaNb₆Cl₁₅ ternary chloride, taking into account electronic effects and the size of the fluorine. The small size of fluorine allows the reduction of the Nb-Nb intracluster distances by steric effects and thus the stabilization of the Ta₆Cl₁₅ structure-type with Nb₆ binary halides.     

A Convenient Procedure for the Synthesis of 6-O-Mono-Phosphate β-Cyclodextrins

Abstract

The synthesis of β-cyclodextrin derivatives bearing one phosphate group on the primary rim is reported. These compounds were prepared in good to excellent yields, by reacting β-cyclodextrin with dialkyl chlorophosphates in the presence of 4-dimethyl amino pyridine (DMAP) catalyst and dimethylformamide (DMF) as solvent. The methodology described is highly selective and the purification of the title compounds is simple, because difficulties due to phosphate regioisomers mixture are avoided.     

Structure and Nonlinear Optical Property of the Cluster Compound V_2S_6O_2Cu_6（3-MePy）_6

A cluster compound V2S6O2Cu6(3-MePy)6(3-MePy = 3-methyl pyridine) has been synthesized by using skiving method and the crystal structure was characterized by X-raydiffraction: space group P1, Z = 1, a = 9.7278(4), b = 10.4180(5), c = 11.9230(6) , α = 108.240(3), β = 98.120(2), γ = 99.500(2)o, R = 0.052 and wR = 0.104. The NLO properties were studied by Z-scan technique with 8 ns pulsed laser at 532 nm. The cluster exhibits strong NLO absorptive ability(α2 = 1.7 × 10–10 m·W–1) and effective self-focusing performance(n2 = 1.27×10–18 m2·W–1) in a 1.58 × 10–4 mol·dm–3 DMF solution.     

On the decrease in the ring π-current upon η6-coordination with a transition metal atom

A synthesis of [10]paracyclophane (Pc) and its organometallic complexes, Pc·Cr(CO)₃, [PcMn(CO)₃]⁺BF₄ ^–, (PcRuC₅Me₅)⁺·PF₆ ^–, (PcRhC₅Me₅)²⁺(BF₄ ^–)₂, and PcCo₄(CO)₉ has been carried out. The¹H NMR spectra of mononuclear complexes of neutral Cr and monocationic derivatives of Mn and Ru have been examined. ⁶-Coordination with a transition metal atom causes a decrease in the ring -current which is exhibited as a downfield displacement of the resonance signals from the protons of the --CH₂ groups in relation to those of free Pc. In the monocationic complexes the deshielding action of the positive charge is also added to this effect. In the¹H NMR spectrum of the cluster PcCo₄(CO)₉ the resonance signals from the --CH₂ protons are shifted upfield in relation to the Pc signals. Consequently, the concept of the ring -current decrease needs more detailed investigation for cluster systems.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1467–1470, August, 1993.     

Resonance effects on the inner-valence levels of SF6 in the photon-energy range 52–72 eV

We report the photoionization partial cross section and asymmetry parameter in the 52–72 eV photon-energy range for the inner-valence orbitais (3t_1u, 2e_g, and 4a_1g) in gaseous SF₆. These results, combined with those for the (inner valence)/(outer valence) branching ratio, indicate resonant enhancement of the inner-valence levels at ≈ 59 eV photon energy which we associate with the 3t_1u → e_g shape resonance predicted by MSM Xα calculations.     

Synthesis of the [(η6-p-cymene)Ru(dppb)Cl]PF6 complex and catalytic activity in the transfer hydrogenation of ketones

Catalysis under mild conditions is of great importance to various chemistry areas, particularly for the development of novel active compounds and for natural products modifications, among others. In this study, the synthesis, characterization, and evaluation of the catalytic activity of a new ruthenium(II) compound, [(η⁶-p-cymene)Ru(dppb)Cl]PF₆ (A) where dppb=1,4-bis(diphenylphosphine)butane, is presented. Catalytic activity of the new Ru(II) compound was tested on hydrogen transfer reaction in various substrates, acetophenone, benzophenone, cyclohexanone, and methyl-ethyl-ketone. Potassium hydroxide was used as base, whereas isopropanol served as both solvent and hydrogen source. Samples comprising substrate: base: catalyst at a 200?:?20?:?1 ratio were poured into 5 mm tubes and monitored in situ at 40, 50, and 60 °C in a 600 MHz NMR spectrometer. The complex was active in the transfer hydrogenation of ketones, achieving conversions superior to 90% within 4 h at 60 °C, which suggests under mild conditions. Therefore, in situ monitoring the reactions through ¹H NMR was a valuable technique to establish the possible catalytic mechanism of Ru(II) precatalyst.     

Influence of Cu6PS5І superionic nanoparticles on the dielectric properties of 6СВ liquid crystal

Influence of Cu₆PS₅? nanoparticles on the dielectric properties of planarly oriented 6СВ liquid crystal (LC) is studied in the 10–10⁶-Hz frequency range. Introduction of the nanoparticles is shown to result in an increase of the electric conductivity. Contrary to 6СНВТ LC, the conductivity monotonously depends on the nanoparticles’ concentration. The main reason of the much greater influence of Cu₆PS₅? nanoparticles on the 6СВ conductivity in comparison with 6СНВТ is related to a greater dissociation coefficient of Cu₆PS₅? in 6СВ than in 6СНВТ. This is confirmed by the fact that the dipole moment of the 6СВ molecules is greater than that of the 6СНВТ molecules.     

Synthesis of the 6-O-methyl-D-glycero-α-L-gluco-heptopyranose moiety present in the capsular polysaccharide from Campylobacter jejuni NCTC 11168

The first synthesis of the 6-O-methyl-D-glycero-α-L-gluco-heptopyranose moiety present in the capsular polysaccharide from Campylobacter jejuni NCTC 11168 is reported. The target (1) was synthesized as the 8-aminooctyl glycoside and then conjugated to bovine serum albumin (BSA) for the generation of antibodies recognizing this motif. Heptose 1 was obtained from D-galactose via a series of galactofuranose derivatives.     

Inner Sphere Reorganization Energy for the Electron Transfer Reactions between M-C_6H_6 and M~ -C_6H_6 Complexes in Gaseous phase: An ab initio Computation

IntroductionTheelectrontransfer(ET)reactionisanfundamentalchemicalprocessandhasbecomethefocusoftheoreticalandexperimentalstudies1-3.AsuitableapproachtowardunderstandingtheETreactivitypatternsistoseparatethevariouscontributionsintoexponentialandpre-exponentialfactors.Theexponentialparts,i.e.,theFrank-Condonfactor,isacompositeofthestructuralreorganizationofthereactingsystemimmediate1yaftertheelectrontransfered.Basedonthecharacteristicsofthereactingsystem'sstructure,thereorganizationenergy(RE…     

Enhanced hydrogen evolution from the face-sharing[RuO6]octahedral motif

Hampered by the ambiguous mechanism of hydrogen evolution reaction(HER)in basic media,the exploration of highly efficient catalytically active sites for alkaline HER is of significance.Herein,a metal oxide Sr₄Ru₂O₉engineering a face-sharing[RuO₆]octahedra motif was synthesized through the solid-state method,and served as HER electrocatalyst.Benefited from the Ru-Ru metallic bonding crossing the common plane,the H*adsorption and reaction energy barriers were optimized.Sr₄Ru₂O₉only required an ultra-small overpotential(η10)of 28 m V at a current density of 10 mA cm^-2 for HER in 1.0 M KOH with an exceptional stability(180 hours),outperforming the commercial Pt/C(η10=38 mV).These findings suggest a fresh insight in designing novel active sites for electrocatalysis.     

A Conformational Study on the Interaction of Saporin-S6 with Phospholipid Vesicles

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Asymmetric synthesis of the C1–C6 portion of the psymberin using an Evans chiral auxiliary

The C1–C6 region of the potent cytotoxic agent psymberin has been synthesized. The key transformations of the synthesis are an auxiliary-controlled addition of a Sn(II)-glycolate enolate to an aldehyde to yield the anti-aldol product and transforming the primary alcohol into a terminal olefin utilizing organoselenium chemistry.