Exploring the complexity of supramolecular interactions for patterning at the liquid-solid interface

The use of self-assembly to fabricate surface-confined adsorbed layers (adlayers) from molecular components provides a simple means of producing complex functional surfaces. The molecular self-assembly process relies on supramolecular interactions sustained by noncovalent forces such as van der Waals, electrostatic, dipole-dipole, and hydrogen bonding interactions. Researchers have exploited these noncovalent bonding motifs to construct well-defined two-dimensional (2D) architectures at the liquid-solid interface. Despite myriad examples of 2D molecular assembly, most of these early findings were serendipitous because the intermolecular interactions involved in the process are often numerous, subtle, cooperative, and multifaceted. As a consequence, the ability to tailor supramolecular patterns has evolved slowly. Insight gained from various studies over the years has contributed significantly to the knowledge of supramolecular interactions, and the stage is now set to systematically engineer the 2D supramolecular networks in a "preprogrammed" fashion. The control over 2D self-assembly of molecules has many important implications. Through appropriate manipulation of supramolecular interactions, one can "encode" the information at the molecular level via structural features such as functional groups, substitution patterns, and chiral centers which could then be retrieved, transferred, or amplified at the supramolecular level through well-defined molecular recognition processes. This ability allows for precise control over the nanoscale structure and function of patterned surfaces. A clearer understanding and effective use of these interactions could lead to the development of functional surfaces with potential applications in molecular electronics, chiral separations, sensors based on host-guest systems, and thin film materials for lubrication. In this Account, we portray our various attempts to achieve rational design of self-assembled adlayers by exploiting the aforementioned complex interactions at the liquid-solid interface. The liquid-solid interface presents a unique medium to construct flawless networks of surface confined molecules. The presence of substrate and solvent provides an additional handle for steering the self-assembly of molecules. Scanning tunneling microscopy (STM) was used for probing these molecular layers, a technique that serves not only as a visualization tool but could also be employed for active manipulation of molecules. The supramolecular systems described here are only weakly adsorbed on a substrate, which is typically highly oriented pyrolytic graphite (HOPG). Starting with fundamental studies of substrate and solvent influence on molecular self-assembly, this Account describes progressively complex aspects such as multicomponent self-assembly via 2D crystal engineering, emergence, and induction of chirality and stimulus responsive supramolecular systems.     

Syntheses, Structures and Properties of Two Metal–Iodide Polymers Based on a Flexile N-Donor Ligand

Two novel metal–organic frameworks based on 1,3-bis(imidazol-1-ylmethyl)-benzene (m-bix), namely [(Cu₄I₄)(bix)₂] _n (1) and [HgI₂(bix)] _n (2) have been synthesized and characterized by IR, elemental analysis, thermogravimetry, luminescent properties and X-ray crystallography. The structure of compound 1 exhibits a 1D metal–organic chain composed of Cu₄I₄ clusters and m-bix ligands, and such chains are further united together to generate a 3D supramolecular structure through inter-chain π···π interactions. In compound 2, the HgI₂-bix chains interact each other to form a layer structure through π···π interactions, then the layers are extended to 3D supramolecular architecture through intermolecular C–H···π interactions.     

A 3D Mesomeric Supramolecular Structure of a Cu(II) Coordination Polymer with 1,1′-Biphenyl-2,2′,3,3′-tetracarboxylic Acid and 5,5′-Dimethyl-2,2′-bipyridine Ligands

A novel metal–organic framework {[Cu(H₂bptc)(cbpy)(H₂O)]·(H₂O)} _n (1) has been hydrothermally synthesized through reaction of 1,1′-biphenyl-2,2′,3,3′-tetracarboxylic acid (H₄bptc) with Cu(II) salt in the presence of ancillary nitrogen ligand 5,5′-dimethyl-2,2′-bipyridine (cbpy), and its structure was determined by X-ray diffraction and characterized by elemental analysis, and IR spectrum. The title compound crystallizes in monoclinic space group P2₁/c. Both right- and left-handed helices are detected in the structure. In the ab-plane, adjacent chains are homochiral and parallel to each other, which are connected together by hydrogen bonds to form a 2D supramolecular structure. The supramolecular layers with opposite chirality are arranged alternatively along the c-axis to form a 3D mesomeric supramolecular structure through π···π interactions. The thermal stability of the complex 1 was studied by thermal gravimetric and differential thermal analysis.     

Syntheses,topological analyses and magnetic properties of two 3D supramolecular nickel-organic frameworks constructed from 1,3,5-benzenetricarboxylate and flexible imidazole-based ligands

Two supramolecular nickel-organic frameworks, [Ni(HBTC)(bix)]_n (1) and [Ni₃(BTC)₂(mbix)₃(H₂O)₄]_n · 6nH₂O (2) (bix = 1,4-bis(imidazole-l-yl-methyl)benzene, mbix = 1,3-bis(imidazole-l-yl-methyl)benzene, and H₃BTC = 1,3,5-benzenetricarboxylate), have been hydrothermally prepared by the assembly of H₃BTC, Ni²⁺ with bix or mbix. Compound 1 shows a 2D layer structure, whose 3D supramolecular structure exhibits a fsc topology when hydrogen-bonging interactions between the adjacent layers are taken into account. Compound 2 manifests an unprecedented 2D (3, 4)-connected topological net. The 3D supramolecular framework of 2 is formed through π?π stacking interactions between the adjacent layers. The magnetic studies show that 1 features overall ferromagnetic property whilst 2 presents strong zero-field splitting (ZFS) when treated as a mononuclear model. Furthermore, the IR and TGA properties of 1 and 2 were also studied.     

Formation of 2D supramolecular architectures at electrochemical solid/liquid interfaces

The controlled formation of supramolecular architectures on chloride pre-covered Cu(1 0 0) has been studied by means of in situ scanning tunneling microscopy (STM) in an electrochemical environment. On top of the c(2 × 2)-Cl layer, ordered arrays of supramolecular cavitand structures could be obtained either by a surface assisted assembly of monomer building-blocks (1,1′-dibenzyl-4,4′-bipyridinium molecules) or by a direct adsorption of supramolecular assemblies (metallo-supramolecular squares) from the solution phase. Besides the omnipresent van-der-Waals-like interactions additional electrostatic interactions between the anionic chloride layer and the positively charged (metallo)-organic molecules are supposed to have strong impact on the 2D phase behavior in both cases.The obtained supramolecular entities with their cavities oriented towards the solution phase can be regarded as potential host assemblies for the specific inclusion of guest molecules.     

Supramolecular Architectures in Three Metal(II) Coordination Polymers with 2,5-Dichloroterephthalate and Flexible Bis(Benzimidazole) Ligands

Three supramolecular coordination polymers, namely [Ni(L1)(DCTP)(H₂O)] _n (1), [Cu(L2)(DCTP)] _n (2), [Co(L3)(DCTP)] _n (3) (L1?=?1,5-bis(5,6-dimethylbenzimidazole)pentane, L2?=?1,4-bis(5,6-dimethylbenzimidazole)butane, L3?=?1,4-bis(benzimidazole)-2-butylene) have been hydrothermally synthesized and characterized by single crystal X-ray structure determination, FT-IR, elemental analysis, X-ray powder diffraction (XPD), and thermogravimetric analysis (TGA). CP 1 exhibits 2D 6³ honeycombed network structure, which is further extended into a 3D Moganite (mog) supramolecular framework by classical O–H?O hydrogen-bonding interaction. CPs 2 –3 present 2D (4,4) layers, and 3D supramolecular frameworks that are formed by π–π stacking interactions. Furthermore, the catalytic activities of CPs 1–3 for the degradation of methyl orange in a Fenton-like process has been investigated, and CPs 1–3 show strong photoluminescence properties at room temperature in solid state.     

A New 2D Cd(II) Grid-like Structure Based on Hetero-Chiral Helical Chains: Synthesis, Crystal Structure, Thermal and Luminescent Properties

A new 2D Cd(II) coordination polymer, [Cd(BBI)₄Cl₂] _n (BBI = 1,1′-(1,4-butanediyl)bis (imidazole)) (1), was synthesized under hydrothermal conditions, and characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction crystallography. For complex 1, each Cd(II) ion crystallizes in a [CdN₄Cl₂] six-coordinated slightly distorted octahedral geometry, coordinating to four BBI ligands by Cd–N bonds, completed by two terminal Cl⁻ anions. The characteristic of 2D grid-like layers, from the central Cd(II) ions as knots and BBI ligands as spacers, is the hetero-chiral helical chains of left- and right-hand helixes. Two kinds of π interactions assemble 2D layers into 3D supramolecular architecture in an ···ABC··· packing arrangement. The fluorescent properties were studied in the solid state for its luminescent applications.     

Synthesis, Crystal Structure and Properties of a New 3D Supramolecular Metal–Organic Framework with Stable Tunnels

A flexible polycarboxyl ligand of tetrahydrofuran-2,3,4,5-tetracarboxylic acid (H₄THFTCA) and a common rigid aromatic ligand of 1,10-phenanthroline (phen) have been successfully co-assembled with Cu(NO₃)₂·3H₂O to give out a novel 3D supramolecular metal–organic framework (MOF) compound, [Cu₂(THFTCA)(phen)(H₂O)₂·CH₃CH₂OH·3H₂O] _n (1), by a solution self-assembly process. Compound 1 has been characterized as a 2D layered coordination polymer constructed by THFTCA^4? and Cu²⁺ ions, and the layer present a novel (3.5²)(3².5³.6⁴.7) topological network. Interestingly, the layers are fused each other via strong π–π stacking interactions among adjacent ligands of the terminal phen, so that a 3D supramolecular MOF with 1D rhomboidal tunnels array is formed. The thermogravimetric analysis and corresponding powder X-ray diffraction analysis have revealed that the tunnels structure of 1 could be retained after all guest molecules are removed, and the framework could resist the collapse even heating up to 210?°C. An opinion has also been proposed that the larger accessible volume of the guests means the larger stress on the backbone of the MOF after the guests are removed, and the stress is harmful to the stability of the supramolecular porous structure. Finally, the application properties based on the porous structure have also been primarily evaluated.     

Synthesis, Structure and Luminescence Property of Cadmium(II) Coordination Polymer with Mixed 5-(Oxidediphenylphosphino)isophthalic Acid and 4,4′-Bipyridine Ligands

A new metal–organic framework {[Cd(L)(4,4′-bpy)]₂·5H₂O} _n (1) had been synthesized by hydrothermal reaction of 5-(oxidediphenylphosphino)isophthalic acid, Cd(II) nitrate, NaOH and 4,4′-bipyridine (4,4′-bpy) as co-ligand. The novel compound was characterized by single crystal X-ray diffractometry as well as FTIR spectrum. Adjacent eight-member (C₂Cd₂O₄) rings are connected each other through pairs of L^2? ligands to result in a 1D double chain. Such ribbons are interconnected together by 4,4′-bpy to generate a 2D pillared layer, which are further held together by rich O–H···O hydrogen bonds to give a 3D supramolecular network. Solvent water molecules play an important role to bridge adjacent layers to form a 3D supramolecular architecture. The luminescence property and thermogravimetric analysis of title complex were investigated.     

Hydrothermal syntheses and crystal structures of PbII coordination polymers based on a N,O-donor ligand

In this article, four new lead(II) coordination polymers based on a N,O-donor ligand 2′-(1 H-1,3,7,8-tetraaza-cyclopenta[l]phenanthren-2-yl)biphenyl-2-carboxylic acid (HL) have been hydrothermally synthesized, namely, [PbL₂]·2H₂O (1), [PbL₂]·2H₂O·CH₃CH₂OH (2), [Pb₅L₂(m-BDC)₄]·3H₂O (3) and [Pb₂L₂(p-BDC)] (4), where m-BDC = 1,3-benzenedicarboxylate and p-BDC = 1,4-benzenedicarboxylate. Compound 1 shows a 2D bilayer structure, which is further extended into a 3D supramolecular structure through π–π stacking interactions. Compound 2 shows a 3D supramolecular structure based on a zero-dimensional molecule by π–π stacking interactions of neighboring molecules. Compound 3 shows a 2D layer structure. Compound 4 displays a 1D chain-like structure, which is then stacked by π–π interactions to result in a 2D supramolecular structure. Solid-state luminescent spectra of four lead(II) complexes indicate intense fluorescent emissions.     

A novel 2D organic–inorganic hybrid based on [P2W18O62]6− polyoxoanion and Cu–bbi coordination polymers

A novel 2D compound based on Wells–Dawson polyoxometalates, [Cu₃(bbi)₆(P₂W₁₈O₆₂)] (bbi = 1,1′-(1,4-butanediyl)bis(imidazole)) (1) has been hydrothermally synthesized and characterized by elemental analyse, IR, TG, PXRD and single crystal X-ray diffraction. In compound 1, each Cu²⁺ ion is connected with four adjacent Cu²⁺ ions by bbi ligands along four different directions and each bbi ligand is two-coordinated by two Cu²⁺ ions, which results in an unusual 2D interlink lock-liked layer. Interestingly, two kinds of macrocycles exist in the structure, in which six smaller 33-membered rings are placed end to end to form the larger ones (66-membered macrocycles). The [P₂W₁₈O₆₂]⁶⁻ polyoxoanions as bidentate ‘guest’ is incorporated into the larger macrocycles. These 2D layers are further packed into 3D framework through strong supramolecular interactions. Additionally, electrochemical and electrocatalysis behavior of 1-CPE have been studied in detail.     

Solvates of New Arylpiperazine Salicylamide Derivative-a Multi-Technique Approach to the Description of 5 HTR Ligand Structure and Interactions

A new ligand for 5-HT1A and 5-HT7 receptors, an arylpiperazine salicylamide derivative with an inflexible spacer, is investigated to identify preferred fragments capable of creating essential intermolecular interactions in different solvates. To fully identify and characterize the obtained crystalline materials, various methods including powder and single-crystal X-ray diffraction, solid-state NMR, and thermal analysis were employed, supplemented by periodic ab initio calculations. The molecular conformation in different solvates, types, and hierarchy of intermolecular interactions as well as the crystal packing were investigated to provide data for future research focused on studying protein–ligand interactions. Based on various methods of crystal structure analysis, including the interaction energy calculation and programs using an artificial neural network, a salicylamide fragment was found to be crucial for intermolecular contacts, mostly of dispersion and electrostatic character. A supramolecular 2D kite-type layer of {4,4} topology was found to form in crystals. The closed voids between layers contain disordered solvents, very weakly interacting with the molecule and the layer. It has been postulated that the separation of the layers might be influenced by an increase in temperature or the size of the solvent; hence, only methanol and ethanol hemi-solvates could be obtained from a series of various alcohols.     

稳定的活性物载体--葡糖微球

系统介绍了法国蔻波公司研制开发的一种新型释放体系－葡糖微球。葡糖微球具有独物的仿生结构－围绕一个固态内核排列的超分子，分别通过离子链和疏水作用来包裹和保护亲油性和亲水性的化妆品洗性成分。经测试具有优异的防止如维生素或酶等易变分子的降解，保持被包裹物活性的功效。因其独特的释放体系，很小的粒径被成功地应用于表皮上层活性成分的保持和传输。     

The irreversible crystal transformation of a novel Cadmium(II) supramolecular complex containing planar tetrameric water cluster

A new cadmium complex [CdL₂(CH₃COO)₂] · 3H₂O (1) has been synthesized by the reaction of 2-aminobenzimidazole (L) with cadmium acetate in an aqueous solution, and structurally characterized by single crystal X-ray diffraction and FT-IR spectra. Cyclic planar tetrameric water clusters with C_2h symmetry are observed to be encapsulated in the 3D open supramolecular architecture of 1 by hydrogen bonds interactions. Interestingly, 1 can convert irreversibly into single crystal 1a formulated [CdL₂(CH₃COO)₂] by losing its lattice water molecules at room temperature. Strong intermolecular N–H ⋯ O hydrogen bonds and aromatic rings π–π stacking interactions assemble 1a into another 3D interdigitated supramolecular network.     

Synthesis and Characterization of the New Nano Flowers Lead(II) Coordination Polymer with Hemidirected Coordination Sphere

Nano flowers of a new polymeric lead(II) complex containing the azide anions, [Pb(baea)(N₃)·(N₃)] _n (“baea” is the abbreviation of bis(2-aminoethyl)amine), has been synthesized by a sonochemical method. The new nano-structure was characterized by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, elemental analyses, and IR spectroscopy. Single crystalline material was obtained using a heat gradient applied to a solution of the reagents. Single-crystal X-ray diffraction analyses show that the coordination number for Pb^II ions is five, PbN5 and hold hemidirected coordination geometry. To the best of our knowledge, the 1D coordination polymer interact with each other via supramolecular and weak Pb···N interactions to create 2D supramolecular frameworks.     

A novel helical chainlike nickel(II) coordination polymer containing 1D trigonal channels with water molecule guests

A novel 1D helical nickel coordination polymer, [Ni(TAU)₂(4,4′-bipy)]_n·2nH₂O (TAU = taurine, 4,4′-bipy = 4,4′-bipyridine), was synthesized and its crystal structure has been determined by X-ray diffraction. Each helix interlinks with six adjacent helices through extensive hydrogen bonds to form 3D supramolecular structure, in which 1D trigonal microporous channels filled with water guest molecules exist within the polymer coils. The framework remains intact on removal of guest water molecules which is proved by XPRD and TGA. Variable temperature magnetic susceptibility indicates weak anti-ferromagnetic interactions between the Ni(II) ions.     

Sonochemical Synthesis and Characterization of A Nano-Rod Lead(II) Supramolecular, Three Dimensional Coordination Compound: New Precursor to Produce Pure Phase Nano-Sized Lead(II) Oxide

Nanorods of a lead(II) supramolecular three-dimensional (3D) coordination compound, [Pb(tfpb)₂]_n (1) (Htfpb?=?4,4,4-trifluoro-1-phenyl-1,3-butanedione), was prepared by the sonochemical method. The new nano-structure was characterized by scanning electron microscopy, X-ray powder diffraction, elemental analyses and IR spectroscopy. A single-crystal structure of the compound showed that the coordination number of Pb(II) is eight with six O-donor atoms from the tfpb ligand and two F-donors from anionic ligands. The 3D supramolecular structure of 1 is realized by weak directional C–F···F–C and π–π stacking interactions. After calcination of nano-sized 1 at 500?°C, pure phase nano-sized lead(II) oxide is produced.     

Inorganic-organic hybrid supramolecular material based on the highest connection of a Keggin arsenotungstate with electro-/photo-catalytic properties

An extraordinary supramolecular hybrid material based on the Keggin arsenotungstate, (Hbimb)₃[AsW₁₂O₄₀]·H₂O (1) (bimb = 1,4-bis(imidazol-l-yl)butane) has been synthesized under hydrothermal condition and characterized by elemental analysis, infrared (IR), thermogravimetry (TG), X-Ray Diffractomer (XRD), and single-crystal XRD. In compound 1 the {AsW₁₂O₄₀} cluster is linked to 14 organic ligands through their surface oxygen atoms, which are further embraced by 20 polyanions analogs to form a tightly packed 3D supramolecular network with a (4⁵·6)(4⁵²·6³⁸·8)(4⁹·6)₂ topology via strong hydrogen bonds and supramolecular interactions. Compound 1 represents the highest connectivity of Keggin supramolecular arsenotungstate, which exhibits electrocatalytic behaviors for reduction of H₂O₂ and high efficiency degradation capability for two typical dyes methylene blue (MB) and rhodamine B (RhB) under UV light.     

Effect of matrix−nanoparticle supramolecular interactions on the morphology and mechanical properties of polymer foams

In this study, we report the fabrication of supramolecular polymer nanocomposite foams with a uniform cell structure, high cell density and high expansion ratio using a soft matrix of poly(methyl acrylate‐co‐2‐hydroxyethyl methacrylate) and silica nanoparticle fillers, both functionalized with ureido‐pyrimidinone (UPy) supramolecular groups. Microcellular structures were formed using a batch foaming process at 90 °C under a 9 MPa nitrogen atmosphere. Nanocomposites were characterized and compared before and after the foaming process to investigate the effect of supramolecular interactions on the thermomechanical properties and morphology of the foams. TEM images revealed that while strong inter‐filler supramolecular interactions do not have a positive effect on their dispersion state, matrix?filler interactions derived from hydrogen bonding UPy motifs result in a rather uniform distribution of nanoparticles. Competing filler?filler and matrix?filler supramolecular interactions can be balanced and optimized by adjusting UPy populations along the chains and on the surface of nanoparticles. At a given chain functionality, increasing the nanoparticle loading up to an optimum concentration improves the mechanical properties and formability of the system. Above such concentration strong interactions between fillers, which are not compensated by the matrix, result in large aggregates and consequently undermine the material performance. Supramolecular polymer foams illustrate a similar thermal and viscoelastic behavior to that of neat samples but after foaming, due to the formation of a cellular structure and rearrangement or dissociation of UPy dimers under the foaming conditions, the elastic modulus is reduced. © 2018 Society of Chemical Industry     

2-甲基咪唑-4,5-二羧酸镍配合物的合成及其晶体结构

以配体2-甲基咪唑-4,5-二羧酸与氯化镍反应,合成出了一个新的配合物[Ni(HMIDC-)]2(H2O)2]n;采用单晶X射线衍射方法测定了配合物的晶体结构。结果表明,所合成的配合物属正交晶系,pbca空间群,晶胞参数a=0.683 74 nm,b=1.388 13 nm,c=1.655 19 nm,V=1 570.97 nm3,Z=4,Dc=1.831 g/cm3,F(000)=1 000.0,GOF=1.304。镍原子与两个不同配体H2MIDC中的咪唑上的氮原子、羧基氧原子以及水分子配位,且形成了六配位八面体构型。配合物由分子间氢键构筑成了三维超分子氢键网络结构。