Thermodynamic model of surfactant adsorption on soft liquid crystal interfaces

The Gibbs adsorption isotherm for planar liquid crystal/fluid interfaces is derived using the anisotropic Gibbs-Duhem equation. The Gibbs adsorption isotherm for planar interfaces is used to analyze the adsorption-driven orientation transition in aqueous solutions of anionic surfactants in contact with rodlike uniaxial nematic liquid crystal films. In qualitative agreement with experiments, the model predicts that, as the surfactant concentration increases, the tangential (planar) average molecular orientation of the liquid crystal with respect to the interface undergoes a transition to a normal (homeotropic) orientation. The anchoring coefficient or strength of anisotropic component of the interfacial tension is shown to depend on the surfactant's concentration. Analyzing the response to addition of a co-cation, the model reveals that, as the fractional coverage of the surfactant's chains increases, the interpenetration of liquid crystal molecules between the adsorbed surfactant tails promotes the orientation transition; at even higher surfactant chain concentrations, interpenetration is hindered because of lack of available space and a random surface orientation emerges. Thus, for aqueous surfactant solutions in contact with nematic liquid crystals, increasing the surfactant concentration leads to the following interfacial liquid crystal orientation transition cascade, planar orientation --> homeotropic orientation --> random orientation, which can lead to new sensor capabilities and surface structuring processes.     

Two- and three-dimensional cadmium-organic frameworks with trimesic acid and 4,4'-trimethylenedipyridine

Three novel cadmium-organic frameworks built-up from 1,3,5-benzenetricarboxylate anions (HXBTC(x-3)) and 4,4'-trimethylenedipyridine (TMD) have been hydrothermally synthesized, and characterized using single-crystal X-ray diffraction, thermoanalytical measurements, elemental analysis, and IR and Raman spectroscopies: [Cd(HBTC)(TMD)(2)].8.5H(2)O (I), [Cd(HBTC)(TMD)(H(2)O)].4.5H(2)O (II), and [Cd(2)(BTC)(TMD)(2)(NO(3))].3H(2)O (III), with structures I and II being isolated as a mixture of crystals. Structure I contains an undulating infinite two-dimensional [Cd(HBTC)(TMD)(2)] framework, with a (4,4) topology and rectangular pores, ca. 3.4 x 11.0 A in cross-section, distributed in a herringbone manner. The crystal structure of I is obtained by parallel packing of this 2D framework in an [ABAB.] fashion. Compound II has a porous 3D diamondoid framework with channels running in several directions of the unit cell, which allows 2-fold interpenetration to occur. The most prominent channels are distributed in a brick-wall fashion along the c axis and have a cross-section of ca. 3.2 x 13.2 A. Structure III can be seen as the three-dimensional assembly of binuclear secondary building units (SBU), which leads to a compact, neutral, and coordinatively bonded eight-connected framework, [Cd(2)(BTC)(TMD)(2)(NO(3))], exhibiting an unusual 3(6)4(22) topology. The increased flexibility of the TMD ligands (brought about by the three methylene groups between the two 4-pyridyl rings) can lead, for the same reactive system, to a large variety of crystal architectures.     

Interpenetration Isomerism in Triptycene‐Based Hydrogen‐Bonded Organic Frameworks

We describe an example of “interpenetration isomerism” in three‐dimensional hydrogen‐bonded organic frameworks. By exploiting the crystallization conditions for a peripherally extended triptycene H₆PET, we can modulate the interpenetration of the assembled frameworks, yielding a two‐fold interpenetrated structure PETHOF‐ 1 and a five‐fold interpenetrated structure PETHOF‐ 2 as interpenetration isomers. In PETHOF‐ 1 , two individual nets are related by inversion symmetry and form an interwoven topology with a large guest‐accessible volume of about 80 %. In PETHOF‐ 2 , five individual nets are related by translational symmetry and are stacked in an alternating fashion. The activated materials show permanent porosity with Brunauer‐Emmett‐Teller surface areas exceeding 1100 m² g^?1. Synthetic control over the framework interpenetration could serve as a new strategy to construct complex supramolecular architectures from simple organic building blocks.     

基于双咪唑和二元羧酸配体的配位聚合物的合成、表征和发光性质研究

利用水热法合成了2种新的双咪唑及二元羧酸配体镉配合物[Cd(sdc)(bipe)]·H_2O(1)和[Cd(bpdc)(bipe)(H_2O)](2)[bipe=bis(4-imidazolphenoxy)ethane,H_2sdc=4,4’-sulfonyldibenzoic acid,H_2bpdc=biphenyl-4,4’-dicarboxylic acid].通过元素分析、红外光谱(IR)、X射线单晶衍射和热重分析(TG)等方法对其进行表征,并测试了2种化合物的荧光性质.化合物1展示了一个具有{4~4·6~2}拓扑的(4,4)-连接的sql二维空间网络结构,配体与金属间荷移跃迁化合物2显示了一个具有(4~(12)·6~3)的六连接pcu网状拓扑结构.荧光测试结果显示,配体与金属间发生的荷移跃迁使得化合物1和2的荧光发射峰与配体bipe相比明显发生了红移.     

Deliberate design of an acentric diamondoid metal-organic network

Reaction of 2.5-dicarboxy-1-methylpyridinium (DCMP) chloride and Zn(NO₃)₂·6H₂O in the presence of NaHCO₃ in water gave an expected acentric diamondoid network [Zn(DCMP)₂] with a three-fold interpenetration. With long Zn-Zn separations, very large cavities are formed within each diamondoid network with high propensity to interpenetration, which makes it show a promising non-linear optical property with SHG efficiency approximately 7 times higher than that of potassium dihydrogen phosphate (KDP). The design strategy of ligand through methylation of the corresponding pyrdinecarboxylic acid can be extended to other widely used carboxylic acids, more importantly, to lead to an unsymmetric bifunctional bridging ligand, which is essential for generating polar solids.     

Chiral direction and interconnection of helical three-connected networks in metal-organic frameworks

The control of the interpenetration and chirality of a family of metal-organic frameworks is discussed. These systems contain two- (A) and four-fold (B) interpenetration of helical three-connected networks generated by binding the 1,3,5-benzenetricarboxylate (btc) ligand to a metal center. These frameworks have the general formula Ni(3)(btc)(2)X(m)Y(n).solvent (where X = pyridine or 4-picoline, Y = ethylene glycol, 1,2-propanediol, 1,4-butanediol, meso-2,3-butanediol, 1,2,6-hexanetriol, glycerol). The structural and chemical effects of modifying the alcohol and aromatic amine ligands bound to the metal center include controlling the thermal stability and the degree of interpenetration. Covalent linking of the four interpenetrating networks in the A family and the switching of diol binding from mono- to bidentate are demonstrated. Recognition of chiral diols by the hand of the network helices is investigated by binding an alcohol ligand with two chiral centers of opposite sense to the same helix. This reveals the subtle nature of the helix-ligand interaction.     

Role of chain interpenetration in layer-by-layer deposition of polyelectrolytes

The effects of temperature, pH, and salt concentration on the layer-by-layer (LBL) deposition of sodium poly(styrene sulfonate) (PSS)/poly[2-(dimethylamino)ethyl methacrylate] (PDEM) were investigated by use of a quartz crystal microbalance with dissipation (QCM-D). At pH 4, the frequency change (Deltaf) gradually decreased to a constant, indicating that the polyelectrolyte complexes of the layer were not dissolved. As the layer number increased, the -Deltaf oscillatedly increased, indicating that the thickness of the multilayer increased. At the same time, the dissipation change (DeltaD) oscillatedly increased with the layer number, indicating the chain interpenetration or complexation that led to the alternative swelling-and-shrinking of the outermost layer. For the same layer number, as the temperature increased, the amplitude of DeltaD increased, indicating that the chain interpenetration increased. The thickness also increased with temperature. Further increasing the pH to 7 led to a thicker layer, reflected in the larger amplitude of DeltaD. At pH 10, the polyelectrolytes no longer formed multilayers on the surface because of the lack of electrostatic interactions. On the other hand, the addition of NaCl also led to a thickness increase. The amplitude in DeltaD increased with NaCl concentration, indicating that the chain interpenetration increased. Our experiments indicated that the LBL deposition of polyelectrolytes was dominated by the chain interpenetration. Also, the polyelectrolyte complexes in the layer can redissolve into solution from the surface at a high temperature or a high salt concentration.     

Recent explorations in electrostatic multilayer thin film assembly

New developments in the area of electrostatic layer-by-layer assembly are reviewed, with emphasis on work in the past two years. Advances in fundamental understanding of polyelectrolyte adsorption is addressed, including the use of new probes and experimental techniques which examine final structure, film interpenetration, and control of thickness. Both theoretical and experimental studies of adsorption of weak polyelectrolytes have been addressed. The role of secondary interactions such as hydrogen bonding or dispersion forces on these parameters is a more recent area of focus. Molecular scale order has been achieved in layered films to produce noncentrosymmetric films; further control of the ordering of molecular side groups in these systems could lead to new and interesting electrical and optical properties. Finally, it has been shown that polyelectrolyte multilayers may be templated onto a number of surfaces; these materials can be patterned onto surfaces to make three dimensional microstructures, or grown on a sacrificial colloidal template to form encapsulant membranes.     

Proton Conduction at High Temperature in High-Symmetry Hydrogen-Bonded Molecular Crystals of RuIII Complexes with Six Imidazole-Imidazolate Ligands

A new H-bonded crystal [Ru^III(Him)₃(Im)₃] with three imidazole (Him) and three imidazolate (Im⁻) groups was prepared to obtain a higher-temperature proton conductor than a Nafion membrane with water driving. The crystal is constructed by complementary N−H⋅⋅⋅N H-bonds between the Ru^III complexes and has a rare Icy-c* cubic network topology with a twofold interpenetration without crystal anisotropy. The crystals show a proton conductivity of 3.08×10⁻⁵ S cm⁻¹ at 450 K and a faster conductivity than those formed by only HIms. The high proton conductivity is attributed to not only molecular rotations and hopping motions of HIm frameworks that are activated at ∼113 K, but also isotropic whole-molecule rotation of [Ru^III(Him)₃(Im)₃] at temperatures greater than 420 K. The latter rotation was confirmed by solid-state ²H NMR spectroscopy; probable proton conduction routes were predicted and theoretically considered.     

Helices versus zigzag chains: one-dimensional coordination polymers of Ag(I) and Bis(4-pyridyl)amine

Five one-dimensional coordination polymers were prepared by the reaction of a bent bridging ligand, bis(4-pyridyl)amine (bpa), with an extensive series of AgX salts (X = CF3SO3, PF6, ClO4, NO3). The 1D polymer networks formed with AgCF3SO3 (1), AgPF6 (2.MeCN), and AgClO4 (3.2MeCN) all incorporated MeCN and were found to adopt a zigzag arrangement. The networks formed with AgClO4 (4) and AgNO3 (5) did not contain any solvent and adopted a single-stranded helical arrangement. Two-dimensional H-bonding networks were formed for 1 and 3.2MeCN, with network topologies 4.8(2) and (4, 4), respectively, whereas three-dimensional H-bonded networks of helices were formed for 4, showing an (8, 3)-a network topology, and 5, showing the topology of the alpha-polonium net. The three-dimensional networks both exhibited 4-fold interpenetration. The NO3- anion in 5 appeared to be acting as a template for the 3D structure.     

结晶聚合物品相相容性的研究

通过ＤＳＣ、Ｘ－射线衍射、红外光谱及拉伸试验研究了ＨＤＰＥ与ＬＬＤＰＥ、ＨＤＰＥ与ＬＤＰＥ之间的晶相相容性．结果表明，链结构相近的ＨＤＰＥ和ＬＬＤＰＥ的晶相相容性好，能形成共晶；而链结构差异较大的ＨＤＰＥ和ＬＤＰＥ的晶相相容性较差，倾向于分别结晶，但有部分链段被对方的晶区夹持．不论是支化度大的ＬＤＰＥ链段插入以ＨＤＰＥ为主的晶区，还是支化度小的ＨＤＰＥ链段插入以ＬＤＰＥ为主的晶区，都可破坏晶区的规整性．共晶的形成使共混物的熔点、结晶度、晶粒体积等低于两组份的线性加和，而力学性能，尤其是断裂伸长率，则显著提高，呈协同效应．     

随星形聚氧化乙烯的分子拓扑形状演变的单层片晶图案

以不同臂(Arm)数的星形聚氧化乙烯(PEO)为对象,系统地研究了其在不同温度下结晶的晶体冰花图案.实验中采用的星形PEO样品,其臂数分别为3,4和8(3-arm-PEO,4-arm-PEO和8-arm-PEO)且每臂的分子量均为5000,线形PEO其分子量为5000.显然,随着星形PEO分子臂数的增加,分子拓扑形状的各向异性不断减小.在单层片晶冰花图案研究中发现,随着结晶温度逐渐向平衡熔点靠近,这些PEO样品的结晶冰花图案具有从树枝状晶体转变为海藻状晶体,然后转变为非规整的紧凑形晶体,最后变成多面晶体的变化规律.对细节的分析进一步表明,随着星形PEO分子臂数的增加,由于分子的各向异性减小,导致冰花状晶体的各向异性程度不断减弱,因此从树枝状晶体到海藻状晶体和从树枝状晶体到多面晶体的转变温度也都逐渐降低.将这些转变温度对臂数作图获得的一张形态相图(morphology diagram)说明了星形PEO结晶图案的分子形状依赖性,也阐明了冰花图案形成的大分子拓扑形状效应.     

Metal-organic frameworks constructed from flexible V-shaped ligands: adjustment of the topology, interpenetration and porosity via a solvent system

Three new metal-organic frameworks (MOFs) are designed by the assembly of flexible V-shaped ligands and paddle-wheel second building units (SBUs). The topology, interpenetration numbers and porosity of frameworks have been well controlled by a solvent system.     

The relaxation spectra of polymer networks with different types of topology,ordering, heterogeneity

Many characteristic features of the relaxation spectra of the different types of polymer networks (meshlike and tree-like) manifesting in experimental behaviour are determined by manifold types of local and long-range irregularities or inclusions existing even in the simplest network structures. These irregularities in the local topology, in the fluctuations of the local orientational order existing due to stretching of the chains in the bulk elastomers (even in the non-ordered elastomers), also due to possible LC-ordering, the distribution of chain lengths between junctions and possible existence of cross-link agglomerations and domains at random cross-linking and the influence of the position of the chain element relative to junctions lead to variety of relaxation spectra, frequency and time-dependencies. The long-range hydrodynamic effects in bulk network can also lead to drastic variation of relaxation spectra. The inclusion of elongated rigid particles in polymer gels and network leads to the appearance of new branches of relaxation spectra changing and overlapping the relaxation spectra of the primary network system.     

Construction of two interpenetrating coordination networks based on 4,4′-bis(1H-imidazol-1-yl-methyl)biphenyl and effect of carboxylic acids

To investigate the construction of interpenetrating coordination networks and the effect of ligands, [Zn(bimb)(bdc)]·H₂O (1) and [Zn(bimb)(Hbtc)]·H₂O (2) [bimb?=?4,4′-bis(1H-imidazol-1-yl-methyl)biphenyl; H₂bdc?=?1,2-benzenedicarboxylic acid; H₃btc?=?1,3,5-benzenetricarboxylic acid] were hydrothermally synthesized and characterized by elemental analysis, IR spectra, Powder X-ray diffraction, and thermogravimetric analysis. Complex 1 shows a 3-D uoc type topology with twofold interpenetration. However, 2 exhibits a different 2-D self-penetrating network owing to hydrogen bonds of Hbtc between the two interpenetrating sql sheets, indicating that different carboxylic ligands could affect the interpenetration structures. Photoluminescence of bimb and the two complexes are also studied.     

Isoreticular chiral metal-organic frameworks for asymmetric alkene epoxidation: tuning catalytic activity by controlling framework catenation and varying open channel sizes

A family of isoreticular chiral metal-organic frameworks (CMOFs) of the primitive cubic network topology was constructed from [Zn(4)(μ(4)-O)(O(2)CR)(6)] secondary building units and systematically elongated dicarboxylate struts that are derived from chiral Mn-Salen catalytic subunits. CMOFs 1-5 were synthesized by directly incorporating three different chiral Mn-Salen struts into the frameworks under solvothermal conditions, and they were characterized by a variety of methods, including single-crystal X-ray diffraction, PXRD, TGA, and (1)H NMR. Although the CMOFs 1 vs 2 and CMOFs 3 vs 4 pairs were constructed from the same building blocks, they exhibit two-fold interpenetrated or non-interpenetrated structures, respectively, depending on the steric sizes of the solvents that were used to grow the MOF crystals. For CMOF-5, only a three-fold interpenetrated structure was obtained due to the extreme length of the Mn-Salen-derived dicarboxylate strut. The open channel and pore sizes of the CMOF series vary systematically, owing to the tunable dicarboxylate struts and controllable interpenetration patterns. CMOFs 1-5 were shown to be highly effective catalysts for asymmetric epoxidation of a variety of unfunctionalized olefins with up to 92% ee. The rates of epoxidation reactions strongly depend on the CMOF open channel sizes, and the catalytic activities of CMOFs 2 and 4 approach that of a homogeneous control catalyst. These results suggest that, although the diffusion of bulky alkene and oxidant reagents can be a rate-limiting factor in MOF-catalyzed asymmetric reactions, the catalytic activity of the CMOFs with large open channels (such as CMOFs 2 and 4 in the present study) is limited by the intrinsic reactivity of the catalytic molecular building blocks. The CMOF catalysts are recyclable and reusable and retain their framework structures after epoxidation reactions. This work highlights the potential of generating highly effective heterogeneous asymmetric catalysts via direct incorporation of well-defined homogeneous catalysts into framework structures of MOFs.     

Multicomponent Self-assembly:Spontaneous Formation of a Metallomacrocycle from Two Quinoline Based Linear Ligands and Four Silver(Ⅰ) Nitrates

Using metal ions to control the self-assembly of metallosupramolecules of varying architecture is one of the fascinating developments in supramolecular chemistry[1,2],particularly those concerned with the deliberate construction of molecular aggregates,like helices,rotaxanes,catenanes,knots,cages[3～6] and the crystal engineering of two or three dimensional networks with varied topology and interpenetration[7～10].Coordination bonds have proved themselves to be one of the most useful connectors in supramolecular self-assembly due to their versatile geometrical modes(e.g.linear,trigonal,square plane,tetrahedral,octahedral) in bond formations.By careful design of tailored ligands,various novel supramolecular architectures have been constructed.Recently,angular bi- or tridentate and other polydentate ligands have aroused a special interest,and a variety of molecular squares,boxes and cages[1～14] with internal cavity or void have been reported,in which many nanoscale structures are formed[6,15,16].We have been interested in the construction of metal based supramolecular structures with polydentate ligands[17～20] and herein report a new metallomacrocyclic complex assembled from two linear polydentate ligands and silver(Ⅰ) nitrate.     

Metal-Organic Framework (MOF) Morphology Control by Design

Exerting morphological control over metal-organic frameworks (MOFs) is critical for determining their catalytic performance and to optimize their packing behavior in areas from separations to fuel gas storage. A mechanism-based approach to tailor the morphology of MOFs is introduced and experimentally demonstrated for five cubic Zn₄O-based MOFs. This methodology provides three key features: 1) computational screening for selection of appropriate additives to change crystal morphology based on knowledge of the crystal structure alone; 2) use of additive to metal cluster geometric relationships to achieve morphologies expressing desired crystallographic facets; 3) potential for suppression of interpenetration for certain phases.     

The solid-state structure of calix[4]arene dihydroxyphosphonic acid–l-lysine complex

The solid-state structure of calix[4]arene dihydroxyphosphonic acid with l-lysine shows a high degree of complexity. The system presents three independent molecules of amino acid, all in different conformational structures, associated with four molecules of calixarene, in the presence of a relatively high number of solvent molecules. The general topology of the complex is guided by the layer of two dimeric units of calixarene molecules and by the large network of hydrogen bonds generated by the molecules of lysine. The arrangement of lysine molecules in the crystal generates a 1-D ladder network.     

Temperature Induced Interpenetration Suppression of a Couple of Azo‐based Isomers with a Flexible Second Ligand

Two new azo‐based coordination compounds with a flexible second ligand, crystal 1 (composed with [Zn(adc)(eda)]_n‐1) and crystal 2 (composed with {[Zn(adc)]_0.9568(eda)}_n‐1′ and {[Zn(adc)]_0.0414}_n) have been synthesized as a couple of isomers with different reaction temperature. Adc^2? and eda represent azobenzene‐4,4′‐dicarboxylic ion and 1,2‐ethanediamine, respectively. Single crystal X‐ray diffraction measurement indicates the interpenetration of the above crystals could be suppressed by simply tuning the reaction temperature, that is, the 5‐fold interpenetration which leads to no free volume left in lower temperature synthesized compound [Zn(adc)(eda)]_n‐1 could be reduced to a 4‐fold interpenetration in higher temperature synthesized {[Zn(adc)]_0.9568(eda)}_n‐1′ which results in free volume accounting for 3.6% (31.6 ų per unit cell volume) in crystal 2 . The synthesis, crystal structure and fluorescence spectra of crystals 1 and 2 have been discussed, together with the data of elemental analysis and X‐ray powder diffraction.