Calculation of the effect of pressurizing gases on the resonant modes of single-crystal parallelepiped

Resonant ultrasound spectroscopy provides for an experimental determination of the elastic moduli of a solid sample. The moduli are extracted by matching a theoretically computed resonant spectrum to the experimental vibrational spectrum. To determine the pressure dependence of the moduli, the vibrational spectrum can be taken with the sample in a pressurizing gas. Then the extraction of the intrinsic, pressure dependent moduli requires a theoretical treatment which permits removal of the perturbation of the spectrum due to the surface loading by the pressure and shear waves in the gas. In order to illustrate a treatment which accomplishes this removal, the theoretically computed frequency shifts and the quality factors are reported for two single-crystal parallelepiped pressurized by noble gases.     

Orientational deconvolution of two-dimensional static disorder by a Tikhonov regularized method for 2H solid state NMR of nano-tubular-oriented structures

A general trend of supramolecular chemistry is the building of mesoscopic-oriented nanotubes. When the typical radius of the channel almost fits the mean supramolecular cross-sectional radius, the guest supramolecule is ultraconfined in the channel. In that case, only rotational disorder around the channel axis is allowed. For sufficiently low temperatures, we expect this 2D disorder to be static on the NMR timescale, and it should reflect the local symmetry of the channels. In this article, we show that experiments performed with deuterium single crystal solid-state NMR as a function of rotation around the channel axis may lead to important information concerning the static orientational disorder of the confined supramolecules. Using an inversion method with Tikhonov regularization and a positivity constraint, that also takes into account of the nonideal pulse sequence response, the orientational probability density can be obtained from 1D experiments performed at different angles, even for significant disorder. As a first step, the method is validated on four different theoretical distributions. It is then applied to ²H NMR single crystal experiments performed on an archetype of parallel channels intergrowth compounds: selectively deuterated 1,10-decanedicarboxylic diacids in hydrogenated urea channels. The diacids form one-dimensional infinite hydrogen-bonded chains ultraconfined in urea linear channels.     

Synthesis, crystal structure and characterization of ternary complexes of lanthanide(III) 3,5-di-tert-butyl-γ-resorcylate with substituted pyridine-N-oxide

Twenty one ternary complexes of lanthanide with 3,5-di-tert-butyl-γ-resorcylic acid (L) and seven different substituted pyridine-N-oxides (L^1–7), with compositions of REL₃L^1–7₂·nH₂O (RE=Nd, Gd, Er; L¹=4-picoline-N-oxide; L²=4-phenyl-pyridine-N-oxide; L³=pyridine-N-oxide; L⁴=3-picoline-N-oxide; L⁵=quinoline-N-oxide; L⁶=iso-quinoline-N-oxide; L⁷=4-methoxyl-pyridine-N-oxide; n=0, 1, 2, 5), were synthesized and characterized by means of elemental analysis, electrical conductivity, thermal analysis and IR spectra. The novel crystal structure of ErL₃L³₂·(EtOH) has been determined by a single-crystal X-ray diffraction method. It shows that each erbium ion is linked to three 3,5-di-tert-butyl-γ-resorcylic acid ions through two different types of dentation modes in which only the carboxylate oxygen atoms participate. The coordination geometries of erbium ion can be described as a distorted octa-coordinated bicapped trigonal prism.     

A practical method,NaOCl-mediated,to prepare thiabendazoles via intramolecular amination reaction

A series of new chlorinated thiabendazoles (6a–m) have been synthesized from readily available anilines and 4-cyanothiazole in moderate to good yields. All synthesized compounds were fully characterized using ¹H NMR, ¹³C NMR, IR, and mass spectrometry. Additionally, the structure of the compound (6f) was confirmed by single-crystal X-ray diffraction. In addition, synthesis of 2-substituted benzimidazoles and 2-phenyl benzothiazole was investigated using our optimized conditions and the outcome is presented herein.     

{111}晶面暴露对介孔金红石TiO2单晶光催化产氢的促进作用

光催化反应发生在半导体材料的表面,材料表面的原子/电子结构直接影响光催化剂的活性或选择性。因此,发展具有特定晶面的半导体光催化剂受到各国学者的普遍关注,被认为是调控光催化材料性能的有效途径之一。自2008年yang等首次合成高表面能{001}晶面占优的锐钛矿TiO2单晶以来,控制合成暴露不同晶面TiO2晶体的研究得到了迅猛的发展,已发展了多种方法合成了具有不同晶面的TiO2晶体。研究表明,选择性地暴露特定的活性晶面能够显著地提高光催化剂的活性或者改变光催化反应的选择性。但是,含有完整晶面构型的TiO2单晶样品的颗粒尺寸一般都较大,通常为几微米,因而显著增加了光生载流子传输与分离的难度,并且导致材料较小的比表面积,限制了对光催化活性的进一步提高。能否在合成含特定晶面单晶的同时增加多孔结构成为有效解决这一问题的关键。最近, Crossland等采用晶种模板法成功合成了介孔的锐钛矿TiO2单晶,并且通过光电器件研究证实了采用该思路可进一步提高材料的光电性能。金红石TiO2在光催化全分解水方面具有独特的优势,然而关于多孔单晶金红石TiO2的研究相对较少,尤其是合成热力学不稳定的高表面能{111}晶面完全暴露的多孔金红石单晶面临较大的技术挑战因而一直未见文献报道。本文利用晶种模板法,以TiCl4溶液为含Ti前驱体、NaF为形貌控制剂、采用水热处理制备出不同比例{111}晶面的介孔金红石单晶。我们前期工作表明, NaF可作为形貌控制剂合成低表面能{110)晶面占优的介孔金红石单晶。本文发现,通过改变NaF的添加量,可有效调变{111}/{110}晶面比例,最终合成完全暴露{111}高表面能的介孔金红石TiO2单晶。扫描电镜结果显示,当添加20 mg NaF时,合成{110}占优的具有高长径比的介孔晶体;当NaF用量增加到40 mg时{110}晶面进一步缩短;至80 mg时则制备出{111})高能面完全暴露的金红石TiO2晶体。值得注意的是,对比研究表明,不采用模板合成了与多孔晶体完全相对应的不同{111}/(110}晶面比例的实心金红石晶体。透射电镜及选区电子衍射以及结合X射线衍射进一步证实,多孔的金红石TiO2晶体与实心金红石单晶均都为单晶结构,孔结构贯穿于样品内部且具有较高的晶面结晶性。氮气吸附实验发现,虽然三个不同晶面比例介孔金红石单晶样品间的形貌具有显著的差异,但比表面积非常相近(分别为24,25,28 m2/g),孔径也都为50 nm左右,该值与所用SiO2模板球的直径以及TEM观察结果相一致。光催化产氢性能结果表明,选择性的暴露活性晶面显著提高了光催化活性,仅含高能面{111}的介孔金红石单晶样品具有最高的产氢速率(约800μmol h–1 g–1),比常规{110}晶面占优的介孔单晶样品速率提高了约一倍。尤其比实心单晶样品的产氢速率提高了至少一个数量级,这应归结于介孔结构特性所导致的表面反应活性位增加、电子传输距离缩短以及光吸收增强协同作用的结果。     

席夫碱Cu(Ⅱ)络合物的超分子螺旋手性及其手性光谱

本文通过不同的手性二胺(pn=1,2-丙二胺、chxn=1,2-环己二胺、dpen=1,2-二苯基乙二胺)与脱氢乙酸(dha)缩合,获得了N_2O_2型手性席夫碱配体(dha-en),进而合成了相应的三对手性席夫碱Cu(Ⅱ)络合物([Cu(dha-R/S-pn)](1a和1b)、[Cu(dha-R,R/S,S-chxn)](2a和2b)、[Cu(dha-R,R/S,S-dpen)](3a和3b),对其进行的固体和溶液电子圆二色(ECD)及溶液振动圆二色(VCD)光谱测试表明,这些化合物在固体和溶液状态下的金属中心的主要配位模式和绝对构型基本一致。此外,通过单晶结构分析发现:对于络合物2a/2b以及3a/3b,中心金属Cu(Ⅱ)除了与手性dha-en四齿配位外,还与相邻分子内酯环上的羰基发生弱的轴向配位形成一维超分子螺旋链,即实现了配位键构筑的席夫碱络合物的手性超分子自组装。本文对两对手性络合物2a/2b以及3a/3b的手性结构基元及其与超分子螺旋之间的关系进行了讨论。将本文所获实验VCD光谱数据与文献报道的相关数据进行比对分析,可以相互印证,并呈现一定的绝对构型关联规律且具有手性配位立体化学结构的指纹特征。     

Rhombohedral epitaxy of cubic SiGe on trigonal c-plane sapphire

Highly [1 1 1]-oriented rhombohedral hetero-structure epitaxy of cubic SiGe semiconductor on trigonal c-plane sapphire was achieved and characterized with two new advanced X-ray diffraction methods to control the formation of primary-twin crystals. The formation of twin crystals on (1 1 1) plane was controlled with growth parameters such that the volume percentage of primary-twin crystal was reduced from 40% to 0.3% compared to the majority single crystal. The control of stacking faults can yield single-crystalline semiconductors without defects or improved thermoelectric materials with twinned crystals for phonon scattering while maintaining electrical integrity. In this study, about 94% of all epitaxial layers were fabricated in a single-crystalline phase. We propose the temperature-dependent alignment model of energetically favored majority single-crystalline SiGe layer on c-plane sapphire. This study shows that nearly single-crystalline cubic semiconductors can be grown in the [1 1 1] orientation on the basal (0 0 0 1) planes of selected trigonal crystal substrates.