Supramolecular adducts of mesocyclic diamines with various carboxylic acids: Charge-assisted hydrogen-bonding in molecular recognition

Aggregation of saturated mesocyclic diamine 1,4-diazacycloheptane (dach) or piperazine (pipz) and diversiform carboxylic acids with mono- or di-carboxyls yields a series of novel binary supramolecular adducts via two-point molecular recognition. All the supramolecular assemblies were obtained by solvent evaporation method from different media. X-ray single-crystal diffraction analyses reveal that these supramolecular moieties present 1D chain motif, 2D flat, corrugated sheet structures and 3D CdSO₄, pillar-layered networks through carboxylate-amide N–H⋯O, as well as its proton transfer form N⁺–H⋯O⁻, carboxyl head to tail O–H⋯O, and extended hydrogen-bonding interactions. Their compositions and structures were also confirmed by Fourier transform infrared (FT-IR) spectroscopy. Thermal stability of these binary crystalline adducts has been investigated by thermogravimetric analysis (TGA), suggesting similar thermal stabilities.     

Supramolecular liquid-crystalline materials: molecular self-assembly and self-organization through intermolecular hydrogen bonding

Supramolecular liquid-crystals are molecular complexes formed from different and independent molecular species through specific molecular interactions such as hydrogen bonding. We have recently developed new types of H-bonded liquid-crystalline materials obtained by molecular self-assembly processes: (1) doubly H-bonded liquid-crystalline complexes through a molecular recognition process between 2,6-bis(acylamino)pyridines and benzoic acids, (2) liquid-crystalline polymer blends involving an H-bonding interaction between poly(4-vinylphenol) and a thermotropic main-chain polyester containing a lateral pyridyl substituent, (3) liquid-crystalline networks built through hydrogen bonds between multifunctional H-bonding components. These new materials may bridge a gap between liquid crystals and supramolecular systems.     

A magnetic iron(III) switch with controlled and adjustable thermal response for solution processing

Spin crossover requires cooperative behavior of the metal centers in order to become useful for devices. While cooperativity is barely predictable in solids, we show here that solution processing and the covalent introduction of molecular recognition sites allows the spin crossover of iron(III) sal(2)trien complexes to be rationally tuned. A simple correlation between the number of molecular recognition sites and the spin crossover temperature enabled the fabrication of materials that are magnetically bistable at room temperature. The predictable behavior relies on combining function (spin switching) and structure (supramolecular assembly) through covalent interactions in a single molecular building block.     

Chiral kagomé lattice from simple ditopic molecular bricks

Self-assembly techniques allow for the fabrication of highly organized architectures with atomic-level precision. Here, we report on molecular-level scanning tunneling microscopy observations demonstrating the supramolecular engineering of complex, regular, and long-range ordered periodic networks on a surface atomic lattice using simple linear molecular bricks. The length variation of the employed de novo synthesized linear dicarbonitrile polyphenyl molecules translates to distinct changes of the bonding motifs that lead to hierarchic order phenomena and unexpected changes of the surface tessellations. The achieved 2D organic networks range from a close-packed chevron pattern via a rhombic network to a hitherto unobserved supramolecular chiral kagomé lattice.     

Two-dimensional pentacene:3,4,9,10-perylenetetracarboxylic dianhydride supramolecular chiral networks on Ag(111)

Self-assembly of the binary molecular system of pentacene and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on Ag(111) has been investigated by low-temperature scanning tunneling microscopy, molecular dynamics (MD), and density functional theory (DFT) calculations. Well-ordered two-dimensional (2D) pentacene:PTCDA supramolecular chiral networks are observed to form on Ag(111). The 2D chiral network formation is controlled by the strong interfacial interaction between adsorbed molecules and the underlying Ag(111), as revealed by MD and DFT calculations. The registry effect locks the adsorbed pentacene and PTCDA molecules into specific adsorption sites due to the corrugation of the potential energy surface. The 2D supramolecular networks are further constrained through the directional CO...H-C multiple intermolecular hydrogen bonding between the anhydride groups of PTCDA and the peripheral aromatic hydrogen atoms of the neighboring pentacene molecules.     

Shape‐Persistent Two‐Component 2 D Networks with Atomic‐Size Tunability

Over the past few years, two‐dimensional (2D) nanoporous networks have attracted great interest as templates for the precise localization and confinement of guest building blocks, such as functional molecules or clusters on the solid surfaces. Herein, a series of two‐component molecular networks with a 3‐fold symmetry are constructed on graphite using a truxenone derivative and trimesic acid homologues with carboxylic‐acid‐terminated alkyl chains. The hydrogen‐bonding partner‐recognition‐induced 2D crystallization of alkyl chains makes the flexible alkyl chains act as rigid spacers in the networks to continuously tune the pore size with an accuracy of one carbon atom per step. The two‐component networks were found to accommodate and regulate the distribution and aggregation of guest molecules, such as COR and CuPc. This procedure provides a new pathway for the design and fabrication of molecular nanostructures on solid surfaces.     

An Elaborate Supramolecular Assembly for a Smart Nanodevice for Ratiometric Molecular Recognition and Logic Gates

Ingenious approaches to supramolecular assembly for fabricating smart nanodevices is one of the more significant topics in nanomaterials research. Herein, by using surface quaternized cationic carbon dots (CDots) as the assembly and fluorescence platform, anionic sulfonatocalix[4]arene with modifiable lower and upper rims as a connector, as well as in situ coordination of Tb³⁺ ions, we propose an elaborate supramolecular assembly strategy for the facile fabrication of a multifunctional nanodevice. The dynamic equilibrium characteristics of the supramolecular interaction can eventually endow this nanodevice with functions of fluorescent ratiometric molecular recognition and as a nano‐logic gate with two output channels.     

Syntheses,Structures, and Properties of Five Coordination Polymers Involving Phthalic Acid

Five new coordination polymers Cu(phen)(H2O)(phth)·CH3OH(1), [Cu(2,2'-bipy)(H2O)](phth)·3.5H2O(2), Zn(phen)(phth)(H2O)·1.125H2O(3) and [M(4,4'-bipy)(H2O)2](phth)·2H2O[M=Zn(4), Mn(5)](H2phth=phthalic acid, bipy=bipyridine, phen=1,10-phenanthroline) have been synthesized from the amino acid derivatives(phthalyl-l- valine, H2L) and structurally characterized. H2L was hydrolyzed into phth2– group during the reaction, but the strucure feature was different from that of the complex directly synthesized from H2phth in the reported literature, revealing that H2L played an important role in composing the novel compounds. Compounds 1, 2 and 3 are all 1D chains, but the differences are that compound 1 is further hydrogen-bonded into 2D networks, and compound 2 is further extended into 3D supramolecular network through π-π stacking and hydrogen-bonding interactions. However, compound 3 is a 1D helix chain structure and further links into 2D networks through π-π stacking. Compounds 4 and 5 are isostructural and exhibit the same 2D layers, which are further connected by hydrogen-bonding interactions to form 3D supramolecular network. Antiferromagnetic superexchange was observed for compounds 1, 2 and 5.     

Self-assembly of diorganotin(IV) oxides (R = Me, nBu, Ph) and 2,5-pyridinedicarboxylic acid to polymeric and trinuclear macrocyclic hybrids with porous solid-state structures: influence of substituents and solvent on the supramolecular structure

2,5-Pyridinedicarboxylic acid has been reacted with three different diorganotin(IV) oxides (R = Me, nBu, Ph) to study the molecular and supramolecular structures of the resulting diorganotin(IV) 2,5-pyridinedicarboxylates. It has been found that coordinating solvent molecules can change the supramolecular structure completely. The molecular structures found are either polymeric (zigzag) or cyclotrimeric; the supramolecular arrangements include (i) systems having only loosely bound discrete molecules (van der Waals contacts), (ii) systems having a 2D or 3D hydrogen-bonded structure, and (iii) systems having a 3D polymeric coordination structure. Channels or cavities are formed in several cases. For a particular case, evidence has been provided that molecular aggregation to capsules through hydrogen bonding interactions is possible in solution.     

Self-healing and shape memory functions exhibited by supramolecular liquid-crystalline networks formed by combination of hydrogen bonding interactions and coordination bonding

We here report a new approach to develop self-healing shape memory supramolecular liquid-crystalline (LC) networks through self-assembly of molecular building blocks via combination of hydrogen bonding and coordination bonding. We have designed and synthesized supramolecular LC polymers and networks based on the complexation of a forklike mesogenic ligand with Ag⁺ ions and carboxylic acids. Unidirectionally aligned fibers and free-standing films forming layered LC nanostructures have been obtained for the supramolecular LC networks. We have found that hybrid supramolecular LC networks formed through metal–ligand interactions and hydrogen bonding exhibit both self-healing properties and shape memory functions, while hydrogen-bonded LC networks only show self-healing properties. The combination of hydrogen bonds and metal–ligand interactions allows the tuning of intermolecular interactions and self-assembled structures, leading to the formation of the dynamic supramolecular LC materials. The new material design presented here has potential for the development of smart LC materials and functional LC membranes with tunable responsiveness.

New supramolecular hybrid liquid-crystalline networks exhibiting self-healing and shape memory properties are developed by self-assembly of small components through hydrogen bonding interactions and coordination bonding.     

Soft functional polynuclear coordination compounds containing pyrimidine bridges

In this account, we describe the use of simple pyrimidine derivatives in combination with metal ions to build highly structured molecular architectures containing functional nanoenvironments, cavities and surfaces that can interact with additional species. The supramolecular structure of these systems can be rationally controlled by metal fragment geometry, reaction conditions and presence of templating agents. Thus, the use of transition metals with low coordination numbers or blocked bonding positions in combination with pyrimidines (e.g. 2-hydroxypyrimidine, 4-hydroxypyrimidine, 2,4-dihydroxypyrimidine, 2-aminopyrimidine) leads to the formation of either discrete assemblies, 1D polymers or helixes. When metal ions with higher coordination possibilities are applied instead, 2D and 3D networks are generated. Some of the assemblies built in this way possess functional cavities, pores and surfaces that can interact with additional species by means of hydrophobic, electrostatic, H-bonding interactions and coordinative bonds to give rise to recognition processes. The latter range from molecular recognition in homogeneous phase as well as clathrate formation, to heterogeneous solid-gas and solid-liquid adsorption phenomena. It should be noted that these materials are not rigid but able to undergo guest-induced reorganisation processes even in the solid state. Finally, some of these materials also combine additional interesting magneto-optical properties. Thus, dual systems can be envisaged in which two or more of these properties are present in the same material.     

Stiff,Multistimuli‐Responsive Supramolecular Hydrogels as Unique Molds for 2D/3D Microarchitectures of Live Cells

Supramolecular hydrogels constructed through molecular self‐assembly of small molecules have unique stimuli‐responsive properties; however, they are mechanically weak in general, relative to conventional polymer gels. Very recently, we developed a zwitterionic amino acid tethered amphiphilic molecule 1 , which gave rise to a remarkably stiff hydrogel comparable with polymer‐based agarose gel, retaining reversible thermal‐responsive properties. In this study, we describe that rational accumulation of multiple and orthogonal noncovalent interactions in the supramolecular nanofibers of 1 played crucial roles not only in the mechanical reinforcement but also in the multistimuli responsiveness. That is, the zwitterionic amino acid moiety and the C C double bond unit of the hydrogelator 1 can function as a pH‐responsive unit and a light‐responsive unit, respectively. We also demonstrated that this stiff and multistimuli‐responsive supramolecular hydrogel 1 is applied as a unique mold for 2D and 3D‐patterning of various substances. More significantly, we succeeded in the fabrication of a collagen gel for spatial patterning, culturing, and differentiation of live cells by using hydrogel 1 molds equipped with 2D/3D microspace channels (100–200 μm in diameter).     

How to Make Weak Noncovalent Interactions Stronger

By employing noncovalent interactions, chemists have constructed a variety of molecular aggregates with well‐defined structures and fascinating properties. In fabricating stable and large molecular assemblies, noncovalent interactions with high binding strength are needed. This Concept summarizes some strategies to modify and optimize the structures of building blocks for making weak noncovalent interactions stronger. The strategies include: 1) Preorganization of binding sites; 2) spatial confinement effects; 3) multivalent enhancement; 4) synergistic binding with multiple forces. Examples of the fabrication of supramolecular architectures by utilizing these strategies are presented and discussed. Guidance is offered in the construction and fabrication of stable molecular assemblies and supramolecular materials.     

3D coordination networks based on supramolecular chains as building units: synthesis and crystal structures of two silver(I) pyridyldiethynides

Two silver(I) pyridyldiethynides, [Ag2(3,5-C2PyC2).4CF3CO2Ag.4H2O] ( A) and [Ag 2(3,5-C2PyC2).3AgNO3.H2O](B), were synthesized by reactions of 3,5-diethynylpyridine with silver trifluoroacetate and silver nitrate in high yield, respectively. X-ray crystallographic studies revealed that in A pyridyldiethynide groups connect Ag 11 cluster units to generate 1D supramolecular chains as bridging ligands, where each ethynide group interacts with four silver atoms. These supramolecular chains bearing pyridyl groups are linked by silver ions to form wavelike layers, which are further connected by trifluoroacetate ligands to afford a 3D coordination network. However, B exhibits a different structural feature, where two ethynide groups in one pyridyldiethynide ligand coordinate to three and four silver atoms, respectively. These silver ethynide cluster units are linked through silver-ethynide and argentophilic interactions, leading to a double silver chain by sharing silver atoms in these units. In B, the silver double chains are further connected by bridging pyridyldiethynide groups to generate 2D networks, which interact through the Ag-N coordination bonds between silver atoms and pyridyl groups in the adjacent layers to generate a 3D coordination network. In these two compounds, trifluoroacetate and nitrate groups exhibit different bonding modes, indicating that the counterion is an important factor influencing the structures of supramolecular chains and coordination networks.     

The supramolecular chemistry of organic-inorganic hybrid materials

The combination of nanomaterials as solid supports and supramolecular concepts has led to the development of hybrid materials with improved functionalities. These "hetero-supramolecular" ideas provide a means of bridging the gap between molecular chemistry, materials sciences, and nanotechnology. In recent years, relevant examples have been reported on functional aspects, such as enhanced recognition and sensing by using molecules on preorganized surfaces, the reversible building of nanometer-sized networks and 3D architectures, as well as biomimetic and gated chemistry in hybrid nanomaterials for the development of advanced functional protocols in three-dimensional frameworks. This approach allows the fine-tuning of the properties of nanomaterials and offers new perspectives for the application of supramolecular concepts.     

Crystal Engineering with Multipoint Halogen Bonding: Double Two-Point Donors and Acceptors at Work

The combination of singly or doubly bidentate halogen-bond donors with double bidentate acceptors was investigated as a supramolecular synthon in crystal engineering. The crystal topologies obtained feature novel halogen-bonding motifs like double two-point recognition and infinite chains or networks based on two-point interactions. Induced conformational changes in the double bidentate halogen-bond donors could be exploited to obtain different 1D and 2D networks. All solid-state studies were accompanied by DFT calculations to predict and rationalize the outcome.     

Molecular trapping on two-dimensional binary supramolecular networks

Molecular preferential adsorption on molecular patterned surfaces via specific intermolecular interactions provides an efficient route to construct ordered organic nanostructures for future nanodevices. Here, we demonstrate the preferential trapping of second-layer molecules atop two-dimensional binary supramolecular networks, F(16)CuPc on DIP:F(16)CuPc and 6P:F(16)CuPc systems, respectively, through intermolecular π-π interactions. The formation of the second-layer supramolecular nanostructures, individual molecular dots or linear molecular chains, can be controlled by the underlying molecular networks.     

The role of nonsurface-active species at interfacial molecular recognition by melamine-type monolayers

The main characteristics of Langmuir monolayers are radically changed by molecular recognition of hydrogen bond nonsurface-active species. The change in the thermodynamic, phase, and structural features by molecular recognition of dissolved uracil or barbituric acid by 2,4-di(n-undecylamino)-6-amino-1,3,5-triazine (2C11H23-melamine) monolayers is characterized by combination of surface pressure studies with Brewster angle microscopy (BAM) imaging and Grazing incidence X-ray diffraction (GIXD) measurements. Phase behavior of the 2C11H23-melamine monolayer and morphology of the condensed phase domains are changed drastically, but in a specific way, by molecular recognition of uracil or barbituric acid. The main characteristics of the interfacial system can be essentially affected by the kinetics of the recognition process. Pure 2C11H23-melamine monolayers show only small compact, but nontextured domains. The monolayers of 2C11H23-melamine-uracil assemblies develop well-shaped circular condensed-phase domains having an inner texture with alkyl chains essentially oriented parallel to the periphery and having a striking tendency to two-dimensional (2D) Ostwald ripening. The 2C11H23-melamine-barbituric acid monolayers form large homogeneous areas of condensed phase that transfer at smaller areas per molecule to a homogeneous condensed monolayer. BAM imaging of corresponding assemblies with ((CH3(CH2)11O(CH2)3)2-melamine having modified alkyl chains demonstrates the specific effect of the monolayer component. GIXD results reveal that molecular recognition of pyrimidine derivatives gives rise only to quantitative changes in the two-dimensional lattice structure. The striking differences in the main characteristics between the supramolecular species are related to their different chemical structures. Quantum chemical calculations using the semiempirical PM3 method provide information about the different nature of the hydrogen-bonding-based supramolecular structures.     

Aggregate Engineering in Supramolecular Polymers via Extensive Non-covalent Networks

Aggregate engineering of non-covalent networks endows supramolecular polymers with thermo-mechanical versatility, stimuliresponsive phase transitions and intrinsic damage-healing capabilities. However, most non-covalent networks are vulnerable at elevated temperatures, which suppresses the robustness of supramolecular polymers. Herein, ureidocytosine(UCy) motifs, which are capable of forming extensive non-covalent networks and thus robust molecular aggregates via multivalent hydrogen bonds and aromatic stackings, are proposed to enable precise programming of the thermo-mechanical versatility. Molecular simulations reveal that the enthalpic contributions from the UCy aggregates play dominant roles to compensate the entropic loss from the redistributions of polymeric spacers and stabilize the non-covalent networks over wide temperature windows. Such aggregate-level strategy offers prospects for applications which require thermo-mechanical versatility of supramolecular polymers, such as 3 D printing, microfabrication and damage-healing coating.     

Supramolecular chemistry

The article discusses molecular recognition and overviews the key concepts -storage and retrieval of chemical information by molecular structures, supramolecular reagents and catalysts, molecular transport, semiochemistry and self assembly. The prospects of controlling supramolecular architecture through engineered molecular recognition and design of ‘programmed systems’ controlled by molecular information are also discussed.