Supramolecular Coordination Research Articles

Homologous Series of Flower Phases in Metal–Organic Networks on Au(111) Surface

Supramolecular coordination self-assembly on the solid surface offers great possibilities for creating nanostructures and thin films with unique physicochemical properties. In this work, we present...

Tetraphenylethene-Based Supramolecular Coordination Frameworks with Aggregation-Induced Emission for an Artificial Light-Harvesting System.

Supramolecular coordination is an efficient strategy to construct supramolecular coordination frameworks with predesigned structures, assembled shapes, and specific function. In this work, we report the synthesis, structural characterization, and photophysical property of two tetraphenylethene-based supramolecular coordination frameworks 1a and 1b formed from 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethene (2a) or 1,1,2,2-tetrakis(4-((E)-2-(pyridin-4-yl)vinyl)phenyl)ethene (2b) and a linear difunctional platinum(II) ligand (3a) via coordination-driven self-assembly. Controlled by the specific angularity and geometry of tetraphenylethene (with 60° and 120°) and difunctional Pt(II) linker (with 180°), these supramolecular coordination frameworks possess a well-defined and two-dimensional (2D) rhombic network-type topology with good periodicity and porosity. Given the aggregation-induced emission (AIE) property of tetraphenylethene units and the porosity of frameworks, 1a and 1b have been successfully used as fluorescent platforms and energy donors to fabricate efficient artificial light-harvesting materials with two fluorescent acceptors (Nile Red and Sulforhodamine 101) via noncovalent interactions in aqueous solution. Furthermore, these light-harvesting materials have been applied for promoting cancer cell imaging with a full shift of imaging channels from blue/green channels to the red channel. Thus, this study provides an effective approach to fabricate functional frameworks as fluorescent platforms for developing more fluorescent materials.

A Solid-State Luminescent Cd(II) Supramolecular Coordination Framework Based on Mixed Luminophores as a Sensor for Discriminatively Selective Detection of Amine Vapors.

A novel Cd(II) supramolecular coordination framework containing mixed functionalized luminophore ligands, namely, [Cd(AS)2(phen)2]EtOH or 1 (where AS = 4-aminosalicylate, phen = 1,10-phenanthroline, EtOH = ethanol), was successfully synthesized as a solid-state luminescent sensor for the detection of amine vapors. The single-crystal X-ray diffraction analysis revealed that 1 possesses a three-dimensional (3D) supramolecular framework enclosing ethanol molecule in the lattice. The supramolecular structure is well-stabilized by various noncovalent intermolecular interactions through functional groups of ligands. Compound 1 shows an intense yellow solid-state emission and displays a reversibly discriminative luminescent response to NH3 and ethylenediamine (EDA) vapors through very large blue-shifted luminescent spectra with distinguishable emission colors under UV light. This work reports the first time for selective luminescent sensing of NH3 and EDA vapors with considerably different emission color change. A sensing mechanism has been confirmed by density functional theory and time-dependent density functional theory calculations that agrees well with the experimental results. Also, 1 exhibits a good recyclability over five cycles for sensing of NH3 and EDA vapors.

Dihydrogen Bond Interaction Induced Separation of Hexane Isomers by Self-Assembled Carborane Metallacycles.

Herein, we describe how to utilize dihydrogen bond interactions to achieve alkane recognition and hexane isomer separation. A series of metallacycles based on carborane backbones are presented herein, revealing interdependent B-Hδ-···Hδ+-C proton-hydride interactions. The metallacycles take advantage of these dihydrogen bond interactions for the separation of hexane isomers. We show that the metallacycle 3a, bearing 1,4-di(4-pyridyl)benzene (DPB), can produce n-hexane with a purity of >99% in a single adsorption-desorption cycle from an equimolar mixture of all five isomers of hexane. The isomers 2-methylpentane and 3-methylpentane can be selectively absorbed by metallacycle 4a, which bears 1,2-di(4-pyridyl)ethylene (DPE). The size of the metallacycle, C-H···π interactions, and particularly B-Hδ-···Hδ+-C interactions are the main forces governing the extent of hexane recognition. This work provides a promising principle for the design of supramolecular coordination complexes (SCCs) for the separation of alkanes.

Subcomponent Self-Assembly of Covalent Metallacycles Templated by Catalytically Active Seven-Coordinate Transition Metal Centers

Coordination geometries of transition metals play vital roles in the self-assembly process of supramolecular coordination complexes. Herein, seven-coordinate 3d metal ions were applied as templates and catalytically active sites for subcomponent self-assembly that resulted in a new category of covalent metallacycles. Single-crystal structures showed that the sizes, configurations, and functionalization of covalent metallacycles could be tuned by the selection of rigid dihydrazide, transition metal ions, and prefunctionalized subcomponents, respectively. Moreover, metallacycles decorated with carboxylic groups could be employed as precursors to prepare aerogels through hierarchical self-assembly, which also exhibited high catalytic activity for cycloaddition of CO2 into cyclic carbonates.

Synthesis of metallo-supramolecular materials based on terpyridine functionalized double-decker silsesquioxane with improved complexation efficiency.

Silsesquioxane-based transition-metal complexes have come to the forefront due to the ability of silsesquioxane to control nanostructures and properties. However, some difficulties in complete complexation and purification limit the widespread use of transition-metal-based supramolecular coordination complexes comprising silsesquioxane. Herein, 2 different approaches have been proposed for the synthesis of metallo-supramolecular materials on the basis of ruthenium(II)-terpyridine functional double-layer silsesquioxane (DDSQ) (Tpy/Ru-DDSQ) (Routes 1 and 2). In Route 1, complexation was followed by functionalization of DDSQ with the ligand, whereas in Route 2, complexation was performed before the ligand was inserted into the DDSQ. Tpy/Ru-DDSQ obtained from both approaches was characterized by 1H NMR, X-ray photoelectron spectrometer, and FTIR and found in the same structure. Both methods were fully discussed and their merits were explored. The complexation yield of the routes was similar. However, the results based on NMR and UV-Vis spectroscopy demonstrated that the incorporation rate of DDSQ into the complex was quite high in Route 2. As far as is known, this is the first study based on the effects of complexing Tpy ligands before/after binding to the target compound, particularly to silsesquioxane-based materials.

Supramolecular hydrogel with luminescence tunablility and responsiveness based on co-doped lanthanide and deoxyguanosine complex

Lanthanide (Ln)-based supramolecular hydrogels are a new category of smart optical materials, which are promising for applications in chemistry sensors, bioimaging agents and light-emitting devices. Herein, we report a supramolecular hydrogel with tunable and responsive luminescence, which is based on the assembly of Ln and deoxyguanosine (dG, one of the units of DNA). ESI-TOF-MS, NMR, FTIR, PXRD and simulation results verify the formation of dG/Ln hydrogels. dG/Tb hydrogel emits strong green luminescence, while dG/Eu hydrogel is nonluminous; when Tb is co-doped into dG/Eu, surprisingly we find that co-doped dG/Tb/Eu hydrogel displays tunable luminescence from green, orange to red by simply regulating the stoichiometric ratio of Tb and Eu. A cascade luminescence resonance energy transfer mechanism (from dG to Tb, and to Eu) is proposed in this co-doped system, which is confirmed by luminescence decay curves and emission spectra. Subsequently, luminescence switch is designed based on reversible responsiveness of hydrogel upon Ag+/L-Cys, temperature and pH stimuli via dynamic supramolecular coordination. Our work provides a new route to construct multicolor functional materials.

Acid-responsive dextran-based therapeutic nanoplatforms for photodynamic-chemotherapy against multidrug resistance

Limited by multidrug resistance (MDR) and nonspecific selectivity, free molecular chemotherapies still are inefficient in clinical cancer treatment. Nanoscale therapeutics delivery systems with controllable release capacity have been developed to reverse multidrug resistance and improve anticancer efficacy. Herein, we constructed acid-sensitive dextrin-based nanoplatforms (THDP) to deliver chemotherapies via supramolecular coordination between tetra sodium meso-tetra (sulfonatophenyl)-porphyrin zinc (II) (Zn-TPPS) and histidine modified dextrin-graft-poly (ethylene glycol) (HDP) to reverse multidrug resistance through photodynamic-chemotherapy. The introductions of hydrophilic poly (ethylene glycol) (PEG) not only prevent undesired aggregation under physiological conditions but also enhanced cellular endocytosis effect. Doxorubicin loaded nanoplatforms (THDP@DOX) with a relatively uniform size of average 63 nm exhibited excellent stability in blood circulation. When THDP@DOX was internalized, the acidic intercellular environment could control the chemotherapies release. Moreover, the generated reactive oxygen species by photosensitizer Zn-TPPS with light irradiation could obviously block DOX efflux and ultimately induce apoptosis to effectively reverse multidrug resistance of tumor cells. Meanwhile, the combination of photosensitizers and chemotherapies obviously created an enhanced MDR reversal effect, providing a promising approach for MDR reversal to achieve highly efficient cancer therapeutics.

Metallacycle/Metallacage‐Cored Fluorescent Supramolecular Assemblies with Aggregation‐Induced Emission Properties

AbstractFluorescent supramolecular assemblies have attracted significant attention for their application as bioimaging agents, biological and chemical sensors, light‐emitting materials, and gene and drug vectors. The introduction of supramolecular coordination complexes constructed by the spontaneous formation of dative metal–ligand bonds through coordination‐driven self‐assembly into fluorescent supramolecular assemblies is of particular interest. This is because the introduction of metal coordination renders the synthesized assemblies excellent stability in addition to providing unique emissions that are different from the fluorescent ligands or metal ions. The discovery of aggregation‐induced emission (AIE), wherein the fluorophores are nonfluorescent in the molecular state, but become highly emissive in the aggregate state, presents new chances for fluorescent supramolecular assemblies since such assemblies are often required to be employed at high concentrations or in the solid state. This progress report provides a summary of the recent design, construction, and application of metallacycle/metallacage‐cored fluorescent supramolecular assemblies based on coordination‐driven self‐assembly, wherein the assemblies exhibit AIE properties. Example applications discussed in detail include light‐emitting materials, chemical and biological sensors, bioimaging agents, and cancer therapy. Moreover, several unsolved issues related to metallacycle/metallacage‐cored fluorescent supramolecular assemblies are discussed in the context of possible future applications of this field.

Construction of Supramolecular Liquid-Crystalline Metallacycles for Holographic Storage of Colored Images

Design and construction of new functionalized supramolecular coordination complexes (SCCs) via coordination-driven self-assembly strategy is highly important in supramolecular chemistry and materials science. Herein, we present a family of well-defined metallacycles decorated with mesogenic forklike dendrons through the strategy of coordination-driven self-assembly. Due to the existence of mesogenic forklike dendrons, the obtained metallacycles displayed the smectic A liquid crystal phase at room temperature while their precursors exhibited the rectangular columnar liquid crystal phase. Interestingly, by taking advantage of the electrostatic interactions between the positively charged metallacycle and the negatively charged heparin, the doping of heparin induced a significant change of the liquid-crystalline behaviors of metallacycles. More importantly, the prepared liquid-crystalline metallacycles could be further applied for holographic storage of colored images. Notably, the rhomboidal metallacycle and hexagonal metallacycle gave rise to different holographic performances although they featured a similar liquid crystal phase behavior. Therefore, this research not only provides the first successful example of supramolecular liquid-crystalline metallacycles for holographic storage of colored images but also opens a new door for supramolecular liquid-crystalline metallacycles toward advanced optical applications.

Rational Synthesis of a Hierarchical Supramolecular Porous Material Created via Self-Assembly of Metal-Organic Framework Nanosheets.

Hierarchically porous materials with high stability and tailorable pore characters have potential for mass transfer applications, including bulky molecule capture and separation, heterogeneous catalysis, and drug delivery. The scope of functionalities can be notably broadened by employing metal-organic framework (MOF) sheets with tunable thickness as giant molecular building blocks for self-assembly into hierarchical supramolecular porous coordination materials. However, synthesizing MOF sheets with controllable bulkiness has proved challenging for scientists. We present a rational yet unprecedented bottom-up strategy to prepare a novel two-dimensional MOF sheet [Zn(BPDI)(Py)2] (BPDI = N,N'-bis(glycinyl)pyromellitic diimide; Py = pyridine) with unusual and highly desired tunable thickness. These sheets self-organize into a unique three-dimensional supramolecular coordination material (NEU-1) with tailorable porosity. To assess its technological relevance, NEU-1c is tested as a support of amine sorbent for CO2 capture. Multichannel porous NEU-1c solves the conventional trade-off suffered by supported amine carbon dioxide adsorbents between increasing amine content and decreasing access to amine sites. Our synthesis process opens the door to novel MOF nanosheets and unique hierarchical supramolecular porous materials with tailorable porosity.

Supramolecular Metallacycles and Their Binding of Fullerenes.

The synthesis of a new triaminoguanidinium‐based ligand with three tris‐chelating [NNO]‐binding pockets and C 3 symmetry is described. The reaction of tris‐(2‐pyridinylene‐N‐oxide)triaminoguanidinium salts with zinc(II) formate leads to the formation of cyclic supramolecular coordination compounds which in solution bind fullerenes in their spherical cavities. The rapid encapsulation of C60 can be observed by NMR spectroscopy and single‐crystal X‐ray diffraction and is verified using computation.

Metal-Organic Frameworks as Chemical Nanoreactors: Synthesis and Stabilization of Catalytically Active Metal Species in Confined Spaces.

Since the advent of the first metal-organic frameworks (MOFs), we have witnessed an explosion of captivating architectures with exciting physicochemical properties and applications in a wide range of fields. This, in part, can be understood under the light of their rich host-guest chemistry and the possibility to use single-crystal X-ray diffraction (SC-XRD) as a basic characterization tool. Moreover, chemistry on preformed MOFs, applying recent developments in template-directed synthesis and postsynthetic methodologies (PSMs), has shown to be a powerful synthetic tool to (i) tailor MOFs channels of known topology via single-crystal to single-crystal (SC-SC) processes, (ii) impart higher degrees of complexity and heterogeneity within them, and most importantly, (iii) improve their capabilities toward applications with respect to the parent MOFs. However, the unique properties of MOFs have been, somehow, limited and underestimated. This is clearly reflected on the use of MOFs as chemical nanoreactors, which has been barely uncovered. In this Account, we bring together our recent advances on the construction of MOFs with appealing properties to act as chemical nanoreactors and be used to synthesize and stabilize, within their channels, catalytically active species that otherwise could be hardly accessible. First, through two relevant examples, we present the potential of the metalloligand approach to build highly robust and crystalline oxamato- and oxamidato-MOFs with tailored channels, in terms of size, charge and functionality. These are initial requisites to have a playground where we can develop and fully take advantage of singular properties of MOFs as well as visualize/understand the processes that take place within MOFs pores and somehow make structure-functionalities correlations and develop more performant MOFs nanoreactors. Then, we describe how to exploit the unique and singular features that offer each of these MOFs confined space for (i) the incorporation and stabilization of metals salts and complexes, (ii) the in situ stepwise synthesis of subnanometric metal clusters (SNMCs), and (iii) the confined-space self-assembly of supramolecular coordination complexes (SCCs), by means of PSMs and underpinned by SC-XRD. The strategy outlined here has led to unique rewards such as the highly challenging gram-scale preparation of stable and well-defined ligand-free SNMCs, exhibiting outstanding catalytic activities, and the preparation of unique SCCs, different to those assembled in solution, with enhanced stabilities, catalytic activities, recyclabilities, and selectivities. The results presented in this Accounts are just a few recent examples, but highly encouraging, of the large potential way of MOFs acting as chemical nanoreactors. More work is needed to found the boundaries and fully understand the chemistry in the confined space. In this sense, mastering the synthetic chemistry of discrete organic molecules and inorganic complexes has basically changed our way of live. Thus, achieving the same degree of control on extended hybrid networks will open new frontiers of knowledge with unforeseen possibilities. We aim to stimulate the interest of researchers working in broadly different fields to fully unleash the host-guest chemistry in MOFs as chemical nanoreactors with exclusive functional species.

X‐ray structure of host‐guest nanosized organotin supramolecular coordination polymer based on cobalt cyanide and quinoxaline as an efficient catalyst for treatment of waste water

New host‐guest supramolecular coordination polymer catalyst 3∞[Co(μ2CN)5(CN)(μ2‐Me3Sn)2(Me3Sn)(H2O)(qox)], SCP1 (qox = quinoxaline) has been synthesized and characterized by single crystal X‐ray diffraction, FT‐IR, UV/Visible and fluorescence spectra, thermal and elemental analyses. The tin atoms act as bridges connecting the Co (CN)6 building blocks. The structure of SCP1 exhibits an unusual self‐coordinated host‐guest 3D network with qox as guest molecule. Also, the nanosized1\ was prepared under ultrasonic irradiation while the morphological features of both were examined by TEM and SEM. SCP1 and nanosized1\ are used as heterogeneous catalysts for removal of toxic dyes under UV and ultrasonic irradiation. The results show high effectively decolorized of indigo carmine dye (IC) without generation of any hazardous wastes or byproducts. The reaction is first order with respect to IC, while the factors affecting the rate constant of the degradation reaction are investigated. Mineralization of IC was investigated by IR and UV spectra. The trapping experiments were carried out to determine the role of active species used for degradation of the dye. The activation parameters of the reaction have been estimated and a possible mechanism of degradation was proposed and discussed in detail.

Emissive Platinum(II) Cages with Reverse Fluorescence Resonance Energy Transfer for Multiple Sensing.

It is quite challenging to realize fluorescence resonance energy transfer (FRET) between two chromophores with specific positions and directions. Herein, through the self-assembly of two carefully selected fluorescent ligands via metal-coordination interactions, we prepared two tetragonal prismatic platinum(II) cages with a reverse FRET process between their faces and pillars. Bearing different responses to external stimuli, these two emissive ligands are able to tune the FRET process, thus making the cages sensitive to solvents, pressure, and temperature. First, these cages could distinguish structurally similar alcohols such as n-butanol, t-butanol, and i-butanol. Furthermore, they showed decreased emission with bathochromic shifts under high pressure. Finally, they exhibited a remarkable ratiometric response to temperature over a wide range (223-353 K) with high sensitivity. For example, by plotting the ratio of the maximum emission (I600/I480) of metallacage 4b against the temperature, the slope reaches 0.072, which is among the highest values for ratiometric fluorescent thermometers reported so far. This work not only offers a strategy to manipulate the FRET efficiency in emissive supramolecular coordination complexes but also paves the way for the future design and preparation of smart emissive materials with external stimuli responsiveness.

Supramolecular self-assembled coordination architecture composed of a doubly bis(2-pyridyl)pyrazolate bridged dinuclear CuII complex and 7,7′,8,8′,-tetracyano-p-quinodimethanide radicals

A tetranuclear CuII complex composed of a doubly bpypz− bridged dinuclear CuII complex with TCNQ˙− self-assembles into a 3D supramolecular coordination architecture via complementary weak coordination bonding and π-stacking interactions.

Structures and properties of three new homobinuclear nanosized supramolecular copper coordination polymers derived from carboxylate type ligands and benzimidazole

Three new homobinuclear nanosized supramolecular copper coordination polymers are hydrothermally synthesized by self-assembly reaction of L-tyrosine (Tyr), terephthalic acid (H2bdc), pyromellitic acid (H4btec) and benzimidazole (Hbzim) with copper chloride salt to generate with formula [[Cu2(tyr)2(bzim)2(Cl)2(H2O)2]]n 1, [[Cu2(bdc)2(bzim)2(H2O)6].3H2O]n 2 and [Cu2(H2btec)(bzim)(H2O)6].2H2O]n 3, which have been investigated by elemental analysis, molar conductivity and magnetic measurements, FT-IR and UV-Vis spectroscopy, (TGA/DTA) thermal analysis and X-ray powder diffraction(XRPD) analysis as well as MM2 theoretical calculations. The magnetic moment and electronic spectra of the complexes are certainly indicating the octahedral geometries. Thermal analysis of the complexes confirms the suggested structures and thermal stability. The results of the XRPD analysis and the average nanosized values of the complexes have nanosized supramolecular polymers in the triclinic system. The MM2 theoretical calculations are supported by the proposed structures.

A covalent deprotection strategy for assembling supramolecular coordination polymers from metal-organic cages.

A Cu4L4 metal-organic cage (MOC) composed of amine-protected ligands forms supramolecular coordination polymers (SCPs) upon covalent post-assembly deprotection. The amorphous SCPs form by virtue of aniline-copper coordination and possess a tunable porosity based on the rate of deprotection.

Controllable synthesis of ultrasmall Pd nanocatalysts templated by supramolecular coordination cages for highly efficient reductive dehalogenation

A simple and efficient supramolecular coordination cage (SCC) template-strategy is developed to synthesize Pd nanocatalysts with controllable size and size distribution for highly efficient reductive dehalogenation.

Imine-functionalized polysiloxanes for supramolecular elastomers with tunable mechanical properties

A series of imine-functionalized polysiloxanes were reported for the first time and used to build supramolecular coordination elastomers.