碱土金属Mg外掺杂硼笼B40Mg6的储氢性能

对外掺杂碱土金属Mg的B₄₀硼笼的储氢性能进行了密度泛函理论研究. 结果表明, B₄₀笼含有2个六元环与4个七元环. 多个Mg原子对B₄₀笼进行外掺杂时不会发生成簇现象, 有利于进一步储氢. Mg原子外掺杂的B₄₀笼对H₂分子的平均吸附能介于物理吸附与化学吸附之间(0.1~0.8 eV). 体系的储氢密度达到7.60%(质量分数). 储氢结构能在常温常压下释放H₂分子, 因此, Mg原子外掺杂的B₄₀笼比Mg合金具有更好的储氢性能.     

水合铵硼氧酸盐及其饱和溶液的FTIR和Raman光谱研究

研究了NH₄B₅O₈·4H₂O和(NH₄)₂B₈O₁₃·6H₂O及其饱和溶液于20℃的FTIR和Raman光谱,对振动频率进行了归属.根据振动光谱特征,预测(NH₄)₂B₈O₁₃·6H₂O中所含基本结构单元为[B₇O ₁₁(OH)·B(OH)₃]^2-.首次将Raman光谱中516cm^-1处的强散射峰归属为这一多聚硼氧配阴离子的对称脉冲振动峰,并对以上2种铵硼氧酸盐饱和溶液中硼氧配阴离子的存在形式{B(OH)₃,[B₃O₃(OH)₄]^-和[B₅O₆(OH)₄]^-}和相互作用机理进行了探讨.     

B3N3H6…CO复合物中弱相互作用竞争的理论研究

本文在MP2/aug-cc-pVTZ水平下对一氧化碳(CO)和环硼氮烷(B₃N₃H₆)之间的弱相互作用进行理论研究，得到6种稳定的B₃N₃H₆…CO复合物结构。B₃N₃H₆…CO复合物中存在N—H…C/O氢键以及π…π、lp…π相互作用，其中含N—H…C氢键复合物的相互作用能(ΔE)最大，为-1.42 kcal·mol^-1。系统的理论计算结果表明π…π相互作用和N—H…C/O氢键可以成功地与lp…π相互作用竞争。取代基效应结果显示，B₃N₃X₃H₃(X=-NH₂)…CO、B₃N₃H₆…CO、B₃N₃X₃H₃(X...     

用LOL-π分析展示B3N3六元环的离域π电子和芳香性——推荐一个普适性的计算化学实验

B₃N₃独特的六元环结构是研究非苯芳香性的理想模板。本实验在B3LYP-D3(BJ)/def2-TZVP水平上优化了B₃N₃六元环结构并进行频率验证,用Multiwfn3.7(dev)绘制了其LOL-π填色图,完美展示了六元环的离域π电子分布和非苯芳香性特征。实验普适性和可操作性强,安全性高,易于推广。     

十二氢十硼双二乙基硫醚络合物新合成法的研究

本文研究了十氢十硼酸和它的各种盐类的开笼反应,找到了合成十二氢十硼双二乙基硫醚络合物[B₁₀H₁₂·(Et₂S)₂]的两个新方法.其一,以十氢十硼酸为质子源,水为配位的Lewis碱,打开稳定的B₁₀H₁₀^2-笼状骨架,随后用二乙基硫醚处理所得的混合物;其二,以硫酸为质子源,二乙基硫醚为Lewis碱打开B₁₀H₁₀^2-的笼状骨架.与文献方法比较,缩短了反应时间,提高了硼的利用率.这些反应与裂解法制备十氢十硼酸双四乙基铵相结合,完成了一条不经过高毒性的十硼烷(14),而由稳定的简单硼氢化合物制备1,2-二碳代-闭-十二硼烷(12)的新的实用路线.     

过饱和硼酸盐水溶液的Raman光谱

制备了MgO·2B₂O₃-H₂O,Na₂O·5B₂O₃-H₂O和MgO·3B₂O₃-H₂O的过饱和水溶液.采用激光喇曼光谱研究了这些过饱和水溶液,并对光谱频率进行了归属.讨论了过饱和水溶液中硼氧配阴离子的存在形式和相互作用机理.     

镁热还原法制备圆片状氮化硼多晶微粉

采用三氧化二硼(B₂O₃)、氯化铵(NH₄Cl)和镁粉为反应物, 以三氧化二铁(Fe₂O₃)为催化剂, 利用镁热还原法在700～850 ℃下反应, 制备了氮化硼多晶微粉. X射线衍射(XRD)分析表明, 产物为六方相, 晶格常数a=0.2499 nm, c=0.6682 nm. 产物的红外光谱中在790和1380 cm^-1处出现了六方氮化硼的特征吸收峰. 利用扫描电子显微镜(SEM)观察到产物为圆片状颗粒, 平均直径约为0.9 μm, 平均厚度约为100 nm. 讨论了Fe2O3的存在对产物形成的影响.     

金属硼笼化合物—闭合型(closo)铁代十一硼烷的合成

金属硼笼化学是目前硼化学中很活跃的一个领域,如何将金属原子嵌入笼中以及它们的化学性能和应用是人们感兴趣的研究课题.特别是对称性极好的正十六面体,十氢十硼酸双阴离子笼[(B₁₀H₁₀)^2-,(图1)]的金属嵌入困难很大,所以目前虽已合成了几百个各种金属的碳硼烷(12),而它的金属嵌入物却只有两个,即乙氧基取代的巢型(nido)7-铂代十一硼烷(11)(图2)和闭合型邻二镍代十二硼烷(10)(图3).至于闭合型金属嵌入物或除去Pt、Ni以外的Ⅷ_b族其他过渡金属嵌入物的合成,则至今尚未见报道.     

B24N24团簇的结构与稳定性

采用密度泛函理论,在B3LYP/6-31G^*水平下,对B₂₄N₂₄笼状团簇的12种异构体进行了优化,并对它们的几何构型、化学键性质、振动光谱和稳定性进行了探讨.研究表明:具有S₈对称的含有2个八元环、8个四元环和16个六元环的结构h是B₂₄N₂₄笼状团簇最稳定的异构体,只存在B-N键,而无N-N和B-B键.含有五元环结构的稳定性最低.B-B和N-N键对的数目越多,结构的稳定性越低.12种异构体的稳定性顺序为h＞a＞b＞I＞g＞l＞c＞k＞j＞d＞e＞f.     

盐卤硼酸盐化学——Ⅸ.MgB4O7-MgCl2-H2O体系结晶动力学研究

业经确定自日晒浓缩高含硼天然盐卤结晶析出的硼酸盐固相中,存在七水六硼酸镁(MgO·3B₂O₃·7H₂O)和氧柱硼镁石(2MgO·2B₂O₃·MgCl₂·14H₂O)。本工作配制了含5.12%MgO·2B₂O₃等的氯化镁近饱和MgB₄O₇-MgCl₂-H₂O合成卤水,在无扰动条件下使静置结晶析出硼酸盐。     

过饱和五硼酸钠溶液结构

用快速X射线衍射法测量了298和323K时过饱和五硼酸钠溶液的时间空间平均结构,得到了溶液径向分布函数.通过模型设计及理论计算获得了B-B、B-O、O-O、Na-O、Na-B原子对相互作用的理论偏径向分布函数,并讨论了浓度和温度对五硼酸钠溶液结构的影响.在五硼酸钠过饱和溶液中六水合Na+形成八面体结构,其平均配位数随浓度和温度变化不大,作用距离随温度升高及浓度减小而减小;给出了溶液中主要硼酸盐离子B3O3(OH)4-、B5O6(OH)4-和B(OH)3的水合结构,较高温度及较高浓度有利于更高聚合的多聚硼酸根离子的形成;浓度对硼酸盐离子的第一水合层的水合数影响较大,在较浓的五硼酸钠过饱和溶液中,五硼酸根离子的一个端氧单齿配位到Na+上形成离子对,Na-B特征距离为0.328nm.     

Structures and bonding of B4O5 and B4O5− clusters: Emergence of boroxol ring and competition between rhombic B2O2 and hexagonal B3O3 cores

Boron oxide clusters are electron-deficient species with novel structures and bonding, in which the emergence of rhombic and boroxol rings is of interest. We report on computational prediction of the global-minimum structures for two boron oxide clusters: B₄O₅ and B₄O₅⁻. These structures differ distinctly, as established through global machine searches and electronic structure calculations at B3LYP and single-point CCSD(T) levels. While B₄O₅ neutral cluster has a rhombic B₂O₂ core, the B₄O₅⁻ anion features a boroxol B₃O₃ ring. One electron completely changes the potential landscapes. Bonding analyses show that the 4π electron-counting is crucial for a rhombic B O cluster, in contrast to π sextet for a boroxol ring, which underlies the competition between rhombic and boroxol rings in B₄O₅/B₄O₅⁻ clusters. A possible pathway for rhombic-to-hexagonal transformation is proposed based on intrinsic reaction coordinate calculations. Anion B₄O₅⁻ cluster, a new member of the inorganic benzene family, is among the smallest B O species with a free-standing boroxol ring, governed collectively by composition and electron-counting.     

An infrared and Raman study of new lonic-conductor lithium glasses

New vitreous fast ionic conductors in the system B₂O₃Li₂OLiCl are described. The conductivity of these glasses increases with the Li₂O and particularly with the LiCl contents. A Raman and infrared study undertaken to elucidate the “structure” of the glasses and the conduction mechanism indicates that the structure consists of a “covalent” boron-oxygen network, in which LiCl is “diluted” without producing detectable interactions with the latter.     

Determination of the bond-angle distribution in vitreous B2O3 by B double rotation (DOR) NMR spectroscopy

The B–O–B bond angle distributions for both ring and non-ring boron sites in vitreous B₂O₃ have been determined by ¹¹B double rotation (DOR) NMR and multiple-quantum (MQ) DOR NMR. The [B₃O₆] boroxol rings are observed to have a mean internal B–O–B angle of 120.0±0.7° with a small standard deviation, σ_R=3.2±0.4°, indicating that the rings are near-perfect planar, hexagonal structures. The rings are linked predominantly by non-ring [BO₃] units, which share oxygens with the boroxol ring, with a mean B_ring–O–B_non-ring angle of 135.1±0.6° and σ_NR=6.7±0.4°. In addition, the fraction of boron atoms, f, which reside in the boroxol rings has been measured for this sample as f=0.73±0.01.     

An Organically Templated Copper Pentaborate with Infinite Metallo-chains:[Cu(C3N2H4)4][Cu(CH3COO)2(C3N2H4)2(H2O)2][B5O6(OH)4]2

A novel organically templated copper pentaborate, [Cu(C₃N₂H₄)₄][Cu(CH₃COO)₂(C₃N₂H₄)₂(H₂O)₂]‐ [B₅O₆(OH)₄]₂, was synthesized by hydrothermal reaction and characterized by elemental analysis, single‐crystal X‐ray diffraction, FT‐IR spectroscopy, Raman spectroscopy and TGA. The crystal structure of this compound consists of two copper‐centered polyhedra and two discrete [B₅O₆(OH)₄]^? pentaborate anions, which are linked together through intensive hydrogen bonding interactions, forming a 3D framework with large channels along c axis. The discrete pentaborate anions form infinite layers by hydrogen bonds. Moreover, the two crystallographically different octahedral coppers are connected by common oxygen atom to form an infinite chain.     

Synthesis,Structure, and Reactivity of Anionic sp2–sp3 Diboron Compounds: Readily Accessible Boryl Nucleophiles

Lewis base adducts of tetra‐alkoxy diboron compounds, in particular bis(pinacolato)diboron (B₂pin₂), have been proposed as the active source of nucleophilic boryl species in metal‐free borylation reactions. We report the isolation and detailed structural characterization (by solid‐state and solution NMR spectroscopy and X‐ray crystallography) of a series of anionic adducts of B₂pin₂ with hard Lewis bases, such as alkoxides and fluoride. The study was extended to alternative Lewis bases, such as acetate, and other diboron reagents. The B(sp²)–B(sp³) adducts exhibit two distinct boron environments in the solid‐state and solution NMR spectra, except for [(4‐tBuC₆H₄O)B₂pin₂]^?, which shows rapid site exchange in solution. DFT calculations were performed to analyze the stability of the adducts with respect to dissociation. Stoichiometric reaction of the isolated adducts with two representative series of organic electrophiles—namely, aryl halides and diazonium salts—demonstrate the relative reactivities of the anionic diboron compounds as nucleophilic boryl anion sources.     

Über Das System Ba2Gd2/3□1/3U1−xWxO6 sowie hexagonale Perowskite vom 18-

On the System Ba₂Gd_2/3□_1/3U_1?xW_xO₆ and Hexagonal Perovskites of an 18-Layer Type In the system Ba₂Gd_2/3□_1/3U_1?xW_xO₆ the formation of a continuous solid solution series is observed. With x ? 0.9 the mixed crystals have a cubic 1:1 ordered perovskite structure. With x ≥ 0.95 the compounds are polymorphic: besides an cubic 1:1 ordered perovskite type for x = 0.95; 0.99 and 1.00 one hexagonal layer structure exists. This lattice is in all cases rhombohedral (space group R3 m) and represents an 18 L-type. Likewise the compounds Ba₂B□_1/3W^VIO₆ with B^III = Tb-Lu and Y belong to the 18 L-type.     

On the pressure-induced phase transformation in the structure II clathrate hydrate of tetrahydrofuran

A high-pressure phase of the clathrate hydrate of tetrahydrofuran was prepared by freezing a liquid phase of overall composition THF · 7 H₂O under a pressure of 3.0 kbar, or by pressurizing the solid structure II THF hydrate of 255K to 3.4 kbar. Unfortunately, the products recovered at 77K were always mixed phase materials as shown by X-ray powder diffraction. A number of diffraction lines could be indexed in terms of the cubic structure I hydrate with a slightly expanded lattice parameter, 12.08 Å, giving some support to Dyadin's idea that the high pressure phase transition involves a conversion of Structure II to Structure I. Other phases observed in the recovered product include Ice IX and amorphous materials. The reversion of the high pressure sample to the structure II hydrate was followed by differential scanning calorimetry. At ambient pressure, the high pressure sample converts slowly back to Structure II hydrate event at 77K.NRCC No. 35786.     

Über hexagonale Perowskite mit Kationenfehlstellen. VII. Schwingungsspektroskopische Untersuchungen an rhomboedrischen 12 L-Stapelvarianten vom Typ Ba4BII(Re2 □ O12) and Ba4B □1/3 (Re2 □ O12)

On Hexagonal Perovskites with Cationic Vacancies. VII. Vibrational Spectroscopie investigations on the Rhombohedral 12 L-Stacking Polytypes Ba₄B^II(Re₂□O₁₂) and Ba₄B □_1/3 (Re₂ □ O₁₂) For the rhombohedral 12 L stacking polytypes Ba₄B^II(Re₂□O₁₂) and Ba₄B□_1/3(Re₂□O ₁₂), space group R3 m, sequence (3)(1), the lattice consists of groups of three face sharing octahedra with the composition Re₂□O₁₂. They are isolated from each other by the Ba and B ions.The vibrational spectra are interpreted according to the factor group analysis. For the Re₂□O₁₂ unit (symmetry D_3d) the results of a complete vibrational analysis and the calculation of the force constants are reported.     

Über hexagonale Perowskite mit Kationenfehlstellen. XXVII. Die Systeme Ba4−xSrxBIIRe2□O12′, Ba4BCaxRe2□O12 und Ba4−xLaxBIIRe2−xWx□O12 mit BII = Co,Ni

On Hexagonal Perovskites with Cationic Vacancies. XXVII. Systems Ba_4?xSr_xB^IIRe₂□O₁₂, Ba₄B Ca_xRe₂□O₁₂, and Ba_4?xLa_xB^IIRe_2?xW_x□O₁₂ with B^II = Co, Ni In the systems Ba_4?xSr_xB^IIRe₂□O₁₂, Ba₄BCa_xRe₂□O₁₂ and Ba_4?xLa_xB^IIRe_2?xW_x□O₁₂ (B^II = Co, Ni) hexagonal perovskites with a rhombohedral 12 L structure (general composition A₄BM₂□O₁₂; sequence (hhcc)₃; space group R&3macr;m) are observed. With the exception of Ba₄NiRe₂□O₁₂ the octahedral net consists of BO₆ single octahedra and M₂□O₁₂ face connected blocks (type 1). In type 2 (Ba₄NiRe₂□O₁₂) the M ions are located in the single octahedra and in the center of the groups of three face connected octahedra. The two outer positions of the latter are occupied by B ions and vacancies in the ratio 1:1. The difference between type 1 and 2 are discussed by means of the vibrational and diffuse reflectance spectra.