Molecular conformation and structural correlations of liquid D-1-propanol through neutron diffraction

An analysis of neutron diffraction data of liquid deuterated 1-propanol at room temperature to extract its molecular conformation is presented. Being a big molecule with twelve atomic sites, the analysis is tricky and needs careful consideration. The resulting molecular parameters are compared with electron diffraction (gas phase), X-ray diffraction (liquid phase) and MD simulation results. Information about the hydrogen-bonded intermolecular structure in liquid is extracted and nature of the probable molecular association suggested.      

High pressure and low-temperature polymorphism in cyclopentanol

The polymorphism of cyclopentanol (C₅H₁₀O) has been investigated as a function of temperature at ambient pressure and as a function of hydrostatic pressures to 3.7?GPa at room temperature. Differential scanning calorimetry (DSC) and Raman spectra reveal that two plastic phases and two fully ordered crystalline phases are formed during cooling. High pressure Raman and infrared spectra show that cyclopentanol undergoes two-phase transformations. At around 0.6?GPa, the liquid cyclopentanol transforms to a solid plastic structure. On further compression to 1.9?GPa, one fully ordered crystalline phase is observed. Based on pieces of evidence such as peak splitting and emergence of new peaks, it can be concluded that the ordered crystalline structure has a lower symmetry. In addition, the decrease in the wavenumber of the O–H stretching modes at low temperature and high pressure suggests the ordered crystalline phases are characterized by the formation of hydrogen-bonded molecular chains.     

螺双杯[4]芳烃-冠-3醚在溶液中构象的研究

研究了螺双杯[4]芳烃-冠-3醚在溶液状态下的¹H、¹³C、¹H-¹³C HMQC、¹H-¹³C HMBC、¹H-¹H TOCSY等核磁共振谱,对其¹H、¹³C谱进行了归属,确定了室温该化合物在溶液状态下的稳定构象为锥式,并利用2D NOESY近似求出杯芳烃区的各种氢的距离,以此为约束进行了模拟淬火计算,证实了2D NOESY谱中多种羟基存在方式,并利用二维交换矩阵计算得出几种羟基的交换速率及其与溶剂中痕量水的交换速率.     

Room temperature supramolecular columnar liquid crystals formed by hydrogen bonding of isoquinoline derivatives

We report new self-assembled discotic liquid crystals exhibiting columnar mesophases at room temperature, which are constructed by intermolecular hydrogen bonding between the core of 1,3,5-trihydroxybenzene or 1,3,5-cyclohexanetricarboxylic acid and the peripheral molecules of isoquinoline derivatives. The mesomorphic properties of supramolecular liquid crystals were investigated by differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction studies. The self-assembled liquid crystals exhibited rectangular columnar phases (Col_ro) with an ordered stacking structure of the mesogens in a column at room temperature, regardless of the type of the core molecule, due probably to the close-packed aromatic rings around a core molecule and the angular structure in three arms of the discotic mesogen. These room temperature columnar phases are rare examples for the discotic liquid crystals, and our findings in the present study provide a new way to prepare low melting columnar liquid crystalline materials for molecular electronics.     

Far infrared and phase transitions in ferroelectric materials

Abstract

A number of far infrared absorption bands are found in molecular and hydrogen-bonded crystals when there are several formula units in the primitive cell. They are very sensitive to the crystal structure and constitute a convenient probe for looking at small changes in the structure, especially at low temperatures where there is a lack of X-Ray data. As well known examples, the case of LTT (Lithium Thallium Tartrate) where the absorption band observed at 21 cm^?1 at room temperature softens down to 8 cm^?1 at the Curie temperature (T_c = 12 K), and LiNH₄SO₄ which has a phase transition at 26 K, will be considered.

It is less known that some ferroelectric crystals can be studied as very thick single crystal plates (thickness t up to 10 mm) at 4 K, and they show in some cases a far IR transmission that is much higher than expected from the study of thin plates (i.e. t = 20 μm). In fact the transmission does not decrease very much when thickness is higher than some specific value t ₀/2. The crystal is not homogeneous at 4 K. A model with a far IR absorbing surface layer (thickness t ₀/2) and a transparent bulk is a good first approximation.

At some temperature T ₀ located between liquid helium and liquid nitrogen temperatures, the center of the bulk undergoes a phase transition from the absorbing phase into the transparent one. When temperature is still lowered, the transparent phase is extended towards the surface with an incommensurate phase between the surface and the bulk.     

量子效应对液体水结构的影响

利用高灵敏的拉曼光谱系统地研究了由量子效应引起的轻水和重水的结构差异. 测量了5～85 oC的轻水和重水的拉曼光谱,明显地观察到两种水的拉曼光谱谱形的差别. 使用全局拟合方法分析了所有谱图的谱形,结果显示在同一个温度下重水的局部结构要比轻水的结构有序,并且他们结构上的差异随着温度的升高而减少. 另外计算了水结构差异的指标|温度漂移,从低温到高温时这个指标从28 oC减小到18 oC. 这些结构差异表明量子效应在室温范围内也非常重要. 我们还利用Vant't Hoff关系式分析了水分子相互作用能. 这些结构上的细节可以帮助建立更加可靠的水模型.     

离子液体阳离子在空气/[bmim][BF4]水溶液界面的取向和结构

采用和频振动光谱研究了空气/[bmim][BF₄]低浓度水溶液界面的取向结构. 研究发现,在体相浓度非常低时,丁基链具有较大的旁式扭曲,表明此时的取向比较无序;阳离子咪唑环则采取一个较小的取向角. 随着浓度的升高,阳离子咪唑环趋向平躺在界面. 由于链-链相互作用,此时丁基链的旁式扭曲也减小,说明界面分子的取向变得有序. 进一步研究发现,PPP和SPS光谱上甲基反对称的峰存在位移,表明界面丁基链上的甲基存在不同取向或具有不同的化学环境.结果有助于从微观层次理解水溶性离子液体和基于咪唑的表面活性剂在界面上的物理化学行为.     

The conductivity properties of protons in ice and mechanism of magnetization of liquid water

From a study of electrical conductivity of protons in the hydrogen-bonded chains in ice we confirm that the magnetization of liquid water is caused by proton transfer in closed hydrogen-bonded chains occurring as a first order phase transition, through which the ice becomes liquid water. We first study the conductive properties of proton transfer along molecular chains in ice crystals in our model. Ice is a typical hydrogen-bonded molecular system, in which the interaction of localized fluctuation of hydrogen ions (H⁺) with deformation of a structure of hydroxyl group (OH) results in soliton motion of the protons along the molecular chains via ionic and bonded defects. We explain further the quantum conductive properties of proton transfer and determine its mobility and conductivity under constant electric-field using a new theory of proton transfer, which agree with experimental values. From features of first order phase-transition for ice, and some experimental data of pure and magnetized water we confirm further that there are not only free water molecules, but also many linear and closed hydrogen-bonded chains consisting of many polarized water-molecules in the liquid water. Thus a ring proton-current, which resembles to a “molecular current” or a “small magnet” in solids, can occur in the closed hydrogen-bond chains under action of an externally applied magnetic field. Then the water molecules in the closed chains can be orderly arrayed due to the magnetic interaction among these ring proton currents and the externally applied magnetic field. This is just the magnetized effect of the water. In such a case the optical and electronic properties of the water, including the dielectric constant, magnetoconductivity, refraction index, Raman and Infrared absorption spectra, are changed. We determine experimentally the properties of the magnetized water which agree with the theoretical results of our model. However, the magnetized effect of water is, in general, very small, and vanishes at temperatures above 100 ^○C.     

An X-ray diffraction study of liquid chlorine

The static structure of liquid chlorine at room temperature is investigated by means of X-ray diffraction. From comparisons with previous neutron and X-ray data, it appears that most of the discrepancies present in the liquid structure factor between neutron and X-ray studies have been removed. Some experimental difference in the two structure factors still remains and one possible explanation is that the electron density distribution of liquid chlorine differs from that derived within the independent atom approximation.     

氧化槐果碱结构的测定及其振动圆二色谱研究

采用傅里叶红外光谱仪(FTIR)和振动圆二色谱仪(VCD)测量氧化槐果碱固体的红外光谱和振动圆二色谱。采用密度泛函方法(DFT)分别在B3LYP/cc-PVTZ和B3LYP/6-311+G(d, p)水平下,对气相中氧化槐果碱分子结构进行了优化,然后在相同水平下计算了氧化槐果碱的红外光谱(IR)以及振动圆二色谱(VCD)。将实验谱图与理论计算谱图进行对照,以确定氧化槐果碱的实际构象以及构象分布。由对比结果可知：采用B3LYP/6-311+G(d,p)水平下,以吉布斯自由能进行玻尔兹曼加权平均后的理论IR和VCD谱图与实际光谱图最为接近,说明在常温下氧化槐果碱具有A/B-trans C/D-trans和A/B-trans C/D-cis两种优势构象,且玻尔兹曼分布显示两种构象均以一定比例共存,且通过对氧化槐果碱的两种优势构象分析,发现A/B环的立体结构为：椅式-椅式,C/D环的立体结构为：椅式-沙发式。     

Molecular structure of alcohol-water mixtures

We use x-ray emission spectroscopy to elucidate the molecular structure of liquid methanol, water, and methanol-water solutions. We find that molecules in the pure liquid methanol predominantly persist as hydrogen-bonded chains and rings with six and/or eight molecules of equal abundance. For water-methanol solutions we find evidence of incomplete mixing at the microscopic level. Our results provide a new explanation for a smaller entropy increase in the solution due to water molecules bridging methanol chains to form rings.     

Structure of the α-phase of solid methanol

The crystal structure of α-methanol at 15K has been determined from neutron powder diffraction measurements. The structure is orthorhombic, space group P2₁2₁2₁. The molecular geometry is found to be very similar to that in the gas phase, but the methyl group no longer has ideal 3-fold symmetry. The crystal is formed by infinite hydrogen-bonded chains of molecules with adjacent chains ‘pointing’ in opposite directions. The O-H … O hydrogen bonds are almost linear. No phase intermediate between the low temperature α-phase and the high temperature β-phase was found, but a new, metastable phase was discovered.     

室温条件下脉冲CO激光辐射特性

CO气体分子发射激光需要在低温(液氮温度附近)时才容易实现。为在常温条件下实现CO的激光输出,采用横向激励大气压(TEA)脉冲放电的方式对CO气体分子在室温条件下的红外发光辐射性能进行了实验研究。在实验所限定的参数条件下,没有获得FO波段激光辐射,仅实现了FB波段的激光输出。典型的指标为:电光转换效率1%,中心波长5.3μm,辐射能量0.22 J,辐射脉宽(FWHM)700 ns,相当于辐射的峰值功率达到0.3 mW左右;当以500 Hz放电脉冲重复频率运转时,常温条件下还获得了大于百瓦量级的高平均功率辐射输出。     

Structure,thermal behavior,and dielectric properties of new cesium hydrogen sulfate arsenate: Cs<Subscript>2</Subscript>(HSO<Subscript>4</Subscript>)(H<Subscript>2</Subscript>AsO<Subscript>4</Subscript>)

Synthesis and structural characterization by single-crystal X-ray diffraction method, thermal behavior, and electrical proprieties are given for a new compound with a superprotonic phase transition Cs₂(HSO₄)(H₂AsO₄). The title compound crystallizes in the monoclinic system with the P2₁/n space group. The structure contains zigzag chains of hydrogen-bonded anion tetrahedra that extend in the [010] direction. Each tetrahedron is additionally linked to a tetrahedron neighboring chain to give a planar structure with hydrogen-bonded sheets lying parallel to (10ī). The existence of O–H and (S/As)–O bonds in the structure at room temperature has been confirmed by IR and Raman spectroscopy in the frequency ranges 4000–400 cm^?1and 1200–50 cm^?1, respectively. Differential scanning calorimetry analysis of the superprotonic transition in Cs₂(HSO₄)(H₂AsO₄) showed that the transformation to high temperature phase occurs at 417 K by one-step process. Thermal decomposition of the product takes place at much higher temperatures, with an onset of approximately 534 K. The superprotonic transition was also studied by impedance and modulus spectroscopy techniques. The conductivity in the high temperature phase at 423 K is 1.58 × 10^?4 Ω^?1 cm^?1, and the activation energy for the proton transport is 0.28 eV. The conductivity relaxation parameters associated with the high disorder protonic conduction have been examined from analysis of the M”/M”_max spectrum measured in a wide temperature range. Transport properties of this material appear to be due to the proton hopping mechanism.     

Structural organization of pi conjugated highly luminescent molecular material

We report on striking evidence for a room temperature structural phase instability in p-hexaphenyl, inducing a nonplanar conformation of the molecules. Solid state proton NMR and single crystal x-ray diffraction allow the analysis of the organization, the individual dynamics and the involved symmetry breaking. The analysis of Raman spectra above and below room temperature reveals a singular behavior suggesting a modification of the overlap between the electronic wave function induced by the nonplanarity. These results provide a new basis to answer fundamental issues related to molecular and electronic materials and, in particular, luminescent organic devices.     

Infrared Spectra of Dicesium trans-Thetraaquadichlorochromium (III) Chloride

The infrared spectra of trans-Cs2[CrCl2 (H2O)4Cl3 and its deuterated isotopomers were investigated at room and liquid nitrogen temperature and at intermediate temperatures as well. The spectra of the partly deuterated analogues are not in agreement with the crystallographic data [1], perhaps because of the incorrect choice of the space group in which the structure was solved and refined or the presence of disorder in the structure.     

NMR chemical shift study of the methanol—benzene-d6 system

The OH proton chemical shifts of methanol referred to the CH₃ proton in the methanol — benzene-d₆ system have been measured from room temperature up to the supercritical region. MD simulations have also been performed at the same composition as experiment at 575 K. The chemical shift results in the supercritical region are in good agreement with those of pure methanol at the same density within experimental errors. The results of NMR and MD simulation suggest that the hydrogen-bonded structure of methanol is practically not affected by addition of benzene molecules.     

苯乙烯基吡啶类液晶化合物的分子结构及相变过程的光谱研究

通过本乙烯基吡啶和不同脂肪羧酸间的氢键作用构成液晶的方法具有合成路线灵活、简便、易于变化的特点,本文通过变温红外光谱对做为质子受体的苯乙烯基吡啶粉液晶化合物的分子结构和相变过程中分子排列的变化进行了研究,结果表明在液晶分子中象羰基这样的偶极矩较大的极性基团,对分子所处的相态分子间的相互排列比较敏感。在红外光谱中羰基伸缩振动的变化可以看作是液晶分子相态转变的标志。     

高压下正戊醇的构象和氢键研究

压力是一个重要的物理参量,通过调节物质内部分子、原子间距离和相互作用力,可以引起物质结构和构象变化。正醇是一种最简单的羟基代替烷基链末端氢原子的有机物,通过氢键和烷基链之间的作用力结合在一起,被称为氢键液体。氢键的键能较小,在外部压力作用下,氢键容易被压缩而断裂或网络重排,从而导致晶体结构和对称性的改变,对材料的性能产生重要影响。正戊醇是一种短链正醇,结构虽然简单,却可以作为烷基链结构有机物的典型代表。然而,高压下正戊醇的性质研究较少,尤其压力作用下其构象变化和氢键研究尚未见报道,因此正戊醇高压研究有待进一步深入。拉曼光谱和红外光谱是高压研究中常用的谱学测量技术,能够原位探测压力作用下分子内部基团变化,是研究结构、构象和氢键作用的有效手段。基于此,利用金刚石对顶砧装置(DAC),结合拉曼光谱和红外光谱,在0~12.0 GPa压力范围对正戊醇进行了高压研究。实验结果分三部分讨论:(1)研究了压力作用下正戊醇的结构相变行为。压力在3.2 GPa时,拉曼特征峰变锐变窄,同时有特征峰劈裂和新特征峰出现的现象,说明在该压力点发生一次液固相转变。(2)揭示了正戊醇在高压下的构象变化。正戊醇存在两种构象:反式构象和扭曲构象。通过分析两种构象特征峰随压力的变化,发现正戊醇发生液固相转变的过程伴随有构象变化,液态时以扭曲构象为主,固态时以反式构象为主。(3)探究了高压对正戊醇氢键的影响。羟基的特征峰随压力的增加发生红移,说明在加压过程中氢键作用增强。伴随液固相变,羟基特征峰劈裂成多个峰,形成新的氢键网络或团簇,且随压力的增加氢键网络或团簇逐渐增大,说明氢键对压力非常敏感,且对正戊醇晶体结构的稳定起着促进作用。该研究不仅为正戊醇生产应用提供重要的指导作用,同时为其他同类或复杂分子体系的物理和化学特性研究提供参考。