Na2B2S5 and Li2B2S5: Two Novel Perthioborates with Planar 1,2,4-Trithia-3,5-Diborolane Rings

For the first time perthioborates with trigonal planar coordination of boron were prepared. Na₂B₂S₅ (Pnma, a = 12.545(2) Å, b = 7.441(1) Å, c = 8.271(1) Å, Z = 4) and Li₂B₂S₅ (Cmcm, a = 15.864(1) Å, b = 6.433(1) Å, c = 6.862(1) Å, Z = 4) were obtained by reaction of the metal sulfides with stoichiometric amounts of boron and an excess of sulfur (effective molar ratio M:B:S = 1:1:4) at 600°C (650°C) and subsequent annealing. The non-isotypic structures contain exactly planar [B₂S₅]^2? groups consisting of five-membered B₂S₃ rings with one additional exocyclic sulfur on each of the boron atoms. The alkaline metal cations are four-coordinate (lithium) and (four + four)-coordinate (sodium) respectively.     

Lanthanide Nitrido Borates with Six-Membered B3N6 Rings: Ln3B3N6

Metal compounds with heteroatomic ring systems of main group elements are a domain of coordination chemistry. However, lanthanide nitrido borates Ln₃B₃N₆ (Ln=La or Ce; see structure) are synthesized by the reaction of hexagonal boron nitride with LnN. The compounds contain the six-membered B₃N₆ ring, which can be seen as a fragment from one layer of the hexagonal BN structure.     

S_2N_2环夹心配合物的MO研究

根据ＭＡＤ－ＳＣＣ－ＥＨＭＯ法的计算结果,用衡量相对稳定性的三个指标：稳定化能、ＨＯＭＯ－ＬＵＭＯ能隙和重迭集居比较了无机环Ｓ２Ｎ２与有机环的夹心和半夹心配合物的相对稳定性,并用碎片分子轨道法讨论了Ｓ２Ｎ２环分子轨道与过渡金属ｄ轨道间的相互作用以及配合物的成键情况和电子结构．     

Lifetime of the B3Σ−u state of S2

Using the single-photon time correlation method, we have determined the lifetime of the S₂(B³Σ^?_u) state from the decay rate of the fluorescence at 370 nm. A lifetime of 45.0 ± 0.6 ns was measured, and the cross section for fluorescence quenching by S₂ as found to be 81.3 ± 4.7 A². A slight dependence of the lifetime on the wavelength of the excitation source over the range of 280 to 337 nm was observed.     

La2XB3 (X = Cl,Br): A Novel Layered Structure with Planar Boron Nets of B3, B6 and B8 Rings

Two new layered rare earth boride halides, La₂XB₃ (X = Cl, Br) have been synthesized. They crystallize in the space group (No. 174) with a = 7.872(1) Å, c = 8.219(2) Å, V = 441.1(1) ų for the chloride, and with a = 7.834(1) Å, c = 8.440(1) Å, V = 448.6(1) ų for the bromide compound, respectively. The crystals of La₂ClB₃ are twinned resulting in an apparent symmetry P6/mmm (No. 191). In the crystal structure of La₂XB₃, trigonal La₆ prisms are condensed into sheets in the a‐b plane, and the halogen atoms X sandwich the La double layers. The connection of B atoms which center the prisms and rectangular prism faces leads to B nets of B₃, B₆ and B₈ rings embedded between the La atom double layers. The chemical bonding is analyzed for the well ordered bromide, and the characteristic disorder in the chloride is discussed.     

Interaction in the Yb2S3-In2S3 system

A T-x diagram is designed for the Yb₂S₃-In₂S₃ system using physicochemical methods. A complex chemical reaction occurs in the system to yield ternary compounds Yb₃InS₆ (S₁), YbInS₃ (S₂), Yb₃In₅S₁₂ (S₃), and YbIn₃S₆ (S₄). In₂S₃-based limited solid solutions are found. Phases S₁, S₃, and S₄ are formed by peritectic reactions at 1260, 1200, and 1100 K, respectively. Compound S₂ melts congruently at 1390 K. Compound S₃ crystallizes in monoclinic system (a = 10.90 Å, b = 21.01 Å, c = 3.846 Å, β = 96.2°). Compounds S₁ and S₄ crystallize in orthorhombic system (for S₁, a = 16.76 Å, b = 13.70 Å, c = 3.88 Å; for S₄, a = 3.86 Å, b = 11.64 Å, c = 20.98 Å, d _exp = 4.62 g/cm³). Compound S₂ crystallizes in cubic system (a = 10.68 Å).     

Glasses in the La2S3-Ga2S3-Sm2S3 system: Synthesis and physicochemical characterization

The glass formation boundaries in the La₂S₃-Ga₂S₃-Sm₂S₃ system have been determined using physicochemical methods (DTA, thermogravimetry, powder X-ray diffraction, and microstructure examination). The thermal stability and IR spectra of newly synthesized phases have been studied. Glasses of composition (Ga₂S₃)_0.60 (La₂S₃)_0.20 (Sm₂S₃)_0.20 at 865 K are stable in atmospheric oxygen. The IR spectra of binary and ternary glasses are practically identical. The IR bands associated with M-S vibrations in the glasses have higher intensities and appear at higher frequencies than the same bands in the spectra of the crystalline components, which is likely due to the strengthened covalence of the M-S bonds in the glasses.     

Reciprocal system 3Tl2S + Bi2Se3 ↔ 3Tl2Se + Bi2S3

The reciprocal system 3Tl₂S + Bi₂Se₃ ? 3Tl₂Se + Bi₂S₃ has been investigated by DTA, X-ray powder diffraction analysis, and emf measurements. Some polythermal sections and the isothermal section at 500 K of the phase diagram and the projection of the liquidus surface of this system have been constructed, and the types and coordinates of the invariant and univariant equilibria have been determined. The existence of wide regions of quaternary solid solutions based on the binary compounds Tl₂S, Tl₂Se, Bi₂S₃, and Bi₂Se₃, and solid solutions between the temary compounds TlBiS₂ and TlBiSe₂ have been established.     

Section EuNdGa3S7-EuGa4S7 of the ternary system Nd2S3-Ga2S3-EuS

The section EuNdGa₃S₇-EuGa₄S₇ of the ternary system Nd₂S₃-Ga₂S₃-EuS was studied by physicochemical analysis methods (differential thermal, X-ray powder diffraction, and microstructural analyses and microhardness and density measurements). The data obtained were used to construct the state diagram of the section EuNdGa₃S₇-EuGa₄S₇. The section was found to be a quasi-binary section of the ternary system and is of the eutectic type. The coordinates of the eutectic are 64 mol % EuGa₄S₇ and T _melt = 1170 K. A region of solid solutions based on both components was found.     

Metal-free Catalyst B2S Sheet for Effective CO2 Electrochemical Reduction to CH3OH

Considering the problems of high costs, low catalytic activity and selectivity in the metal-based catalysts for CO₂ electroreduction, we apply boron-containing metal-free B₂S sheet as an alternative to the traditional metal-based catalysts. Reaction energy calculations identify the preferred “Formate” pathway for CO₂ conversion to CH₃OH on B₂S, in which the thermodynamic energy barrier obtained by using the Computational Hydrogen Electrode model is 0.57 eV, and the kinetic energy barrier obtained by searching the transition states is 1.18 eV. Another possible reaction pathway, “RWGS+CO-hydro”, is suppressed and the hydrogen evolution reaction (HER) side reaction is nonspontaneous. Compared to Cu(211) with the highest catalytic activity among all transition metals, B₂S sheet exhibits a better catalytic activity with a lower overpotential for CO₂ reduction and a better selectivity that suppresses the non-target reaction.     

Mittlere Schwingungsamplituden für einX(YZ)2-Molekülmodell mit C2v-Symmetrie: Anwendung auf die Moleküle B2O3, B2S3 und S(CN)2

Zusammenfassung Auf Grund von Symmetrieüberlegungen wird eine Methode zur Bestimmung der mittleren Amplitudenquadrate der Schwingungen einesX(YZ) ₂-Molekülmodells mit C_2v Symmetrie entwikkelt. Es werden analytische Ausdrücke für die verschiedenen mittleren Amplitudenquadrate in Termen der symmetrisierten Matrizen der mittleren Amplitudenquadrate erhalten. Die Methode wird auf die Moleküle B₂O₃, B₂S₃ und S(CN)₂ angewendet. Es werden die mittleren Amplitudenquadrate und die mittleren Schwingungsamplituden bei Zimmertemperatur für gebundene und nichtgebundene Atompaare aus den beobachteten Ramanund Infrarotgrundschwingungen sowie den Daten der Molekülstruktur berechnet. Die chemische Bedeutung der beiden verschiedenen charakteristischen Bindungen im Zusammenhang mit anderen Molekülen mit ähnlichen Bindungsverhältnissen wird kurz besprochen. Weiters werden die molaren thermodynamischen Funktionen für das Schwefeldicyanidmolekül im Temperaturbereich von 200 bis 2000° K unter Annahme eines starren Rotator-und harmonischer Oszillator-Modells berechnet.

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Mean amplitudes of vibration for an X(YZ)₂ molecule with C_2v symmetry: Application to B₂O₃, B₂S₃ and S(CN)₂

On the basis of symmetry considerations a method has been developed for the determination of the mean-square amplitudes of vibration for anX(YZ) ₂ molecular model with a C_2v symmetry. Analytical expressions for the various mean-square amplitude quantities in terms of the symmetrized mean-square amplitude matrices have been obtained. The method has been applied to the B₂O₃, B₂S₃, and S(CN)₂ molecules and mean-square amplitude quantities and mean amplitudes of vibration for both bonded and nonbonded atom pairs have been computed at room temperature from the observed Raman and infrared fundamental frequencies as well as molecular structural data. A brief discussion of the results on the chemical significance of the two different characteristic bonds has been made in relation to other molecules having similar chemical bonds. Molar thermodynamic functions for the temperature range 200–2000° K have also been computed for the sulphur dicyanide molecule on the assumption of a rigid rotator, harmonic oscillator model.

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Diese Arbeit wurde durch das Stipendium NGR-41-002-003 der National Aeronautics and Space Administration unterstützt.     

Supramolecular Nanocycles Comprising β‐Cyclodextrin‐click‐Ferrocene Units: Rings of Rings of Rings

We applied 1,3‐dipolar cycloaddition to bind ethynylferrocene onto 6I‐azido‐6I‐deoxycyclomaltoheptaose under microwave assisted conditions. The process was investigated by ¹H NMR, FT‐IR spectroscopy, and MALDI‐TOF mass spectrometry. The ability of the synthesized compound to self‐organize to cyclic supramolecular structures was investigated by dynamic light scattering measurements and cryo‐transmission electron microscopy.

     

Interconversion of (S)-glutamate and (2S,3S)-3-methylaspartate: a distinctive B(12)-dependent carbon-skeleton rearrangement

The interconversion of (S)-glutamate and (2S,3S)-3-methylaspartate catalyzed by B(12)-dependent glutamate mutase is discussed using results from high-level ab initio molecular orbital calculations. Evidence is presented regarding the possible role of coenzyme-B(12) in substrate activation and product formation via radical generation. Calculated electron paramagnetic resonance parameters support experimental evidence for the involvement of substrate-derived radicals and will hopefully aid the future detection of other important radical intermediates. The height of the rearrangement barrier for a fragmentation-recombination pathway, calculated with a model that includes neutral amino and carboxylic acid substituents in the migrating glycyl group, supports recent experimental evidence for the interconversion of (S)-glutamate and (2S,3S)-3-methylaspartate through such a pathway. Our calculations suggest that the enzyme may facilitate the rearrangement of (S)-glutamate through (partial) proton-transfer processes that control the protonation state of substituents in the migrating group.     

Darstellung und Kristallstruktur der Dialkalimetalltrichalkogenide Rb2S3, Rb2Se3, Cs2S3 und Cs2Se3

Preparation and Crystal Structure of the Dialkali Metal Trichalcogenides Rb₂S₃, Rb₂Se₃, Cs₂S₃, and Cs₂Se₃ Crystalline products were obtained by the reaction of the pure alkali metals with the chalcogens in the molar ratio 2:3 in liquid ammonia at pressures up to 3000 bar and temperatures around 600 K. The substances crystallize in the K₂S₃ type structure (space group Cmc2₁(NO. 36)). Unit cell constants see ?Inhaltsübersicht”?. The characteristic feature of this structure are bent polyanions X₃^2?:(X = S,Se). The new described compounds are compared with the other known alkali metal trichalcogenides.     

Die Perthioborate RbBS3, TIBS3 und TI3B3S10

The Perthioborates RbBS₃, TIBS₃, and Tl₃B₃S₁₀ . RbBS₃ (P2₁/c, a=7.082(2) Å, b=11.863(4) Å, c=5.794(2) Å, β=106.54(2)°) was prepared as colourless, plate-shaped crystals by reaction of stoichiometric amounts of rubidium sulfide, boron, and sulfur at 600°C and subsequent annealing. TlBS₃ (P2₁/c, a=6.874(3) Å, b=11.739(3) Å, c=5.775(2) Å, β=113.08(2)°) which is isotypic with RbBS₃ was synthesized from a sample of the composition Tl₂S · 2 B₂S₃. The glassy product which was obtained after 7 h at 850°C was annealed in a two zone furnace for 400 h at 400→350°C. Yellow crystals of TlBS₃ formed at the warmer side of the furnace. Tl₃B₃S₁₀ (P1 , a=6.828(2) Å, b=7.713(2) Å, c=13.769(5) Å, α=104.32(2)°, β=94.03(3)°, γ=94.69(2)°) was prepared as yellow plates from stoichiometric amounts of thallium sulfide, boron, and sulfur at 850°C and subsequent annealing. All compounds contain tetrahedrally coordinated boron. The crystal structures consist of polymeric anion chains. In the case of RbBS₃ and TlBS₃ nonplanar five-membered B₂S₃ rings are spirocyclically connected via the boron atoms. To obtain the anionic structure of Tl₃B₃S₁₀ every third B₂S₃ ring of the polymeric chains of MBS₃ is to be substituted by a six-membered B(S₂)₂B ring.