Supramolecular Metal Research Articles

Phosphines and other P(III)‐derivatives with Cavity‐shaped Subunits: Valuable Ligands for Supramolecular Metal Catalysis, Metal Confinement and Subtle Steric Control

AbstractTertiary phosphines and other P(III)‐derivatives are the par excellence ligands in industrially relevant homogeneous catalysis. A promising, recent development in this field concerns the use of P(III)‐compounds that incorporate cavity‐shaped subunits capable of assisting metal‐centred reactions, either by functioning as receptor moieties, creating confinement about the reactive centre or merely by influencing main catalytic steps via strong steric interactions exerted on the metal first coordination sphere. This Minireview, which is based on selected examples, illustrates the utility of covalently‐constructed phosphines that incorporate a cavity and highlights future directions that deserve development in ligand design.

Crystallization Induced Enhanced Emission in Two New Zn(II) and Cd(II) Supramolecular Coordination Complexes with the 1-(3,4-Dimethylphenyl)-5-Methyl-1H-1,2,3-Triazole-4-Carboxylate Ligand.

Two new d10 metal supramolecular metal–organic frameworks (SMOFs) with general formula [ML2(H2O)2]n (M = Zn, Cd) have been synthetized using the sodium salt of the anionic 1-(3,4-dimethylphenyl)-5-methyl-1H-1,2,3-triazole-4-carboxylate ligand (Na+L−). Both SMOFs have been structurally characterized by single-crystal X-ray diffraction analysis and IR spectroscopy. The compounds are isostructural and form supramolecular aggregates via hydrogen bonds with the presence of less common dihydrogen bonds. Interestingly, they show ionic conductivity and porosity. The luminescent properties have been also studied by means of the excitation and emission spectra. Periodic DFT and molecular TD-DFT calculations have been used to unravel the emergence of luminescence in the otherwise non-emitting 1-(3,4-dimethylphenyl)-5-methyl-1H-1,2,3-triazole-4-carboxylate ligand once incorporated in the SMOFs. Our results also illustrate the importance of considering the dielectric environment in the crystal when performing excited state calculations for isolated fragments to capture the correct electronic character of the low-lying states, a practice which is not commonly adopted in the community.

Supramolecular Metal–Organic Framework for CO2/CH4 and CO2/N2 Separation

Supramolecular metal–organic frameworks (SMOFs) are emerging as a new family of porous materials. In this work, a SMOF, [Cu2(ade)4(H2O)2](SiF6)2 (SMOF-SIFSIX-1, ade = adenine) was successfully synthesized from the cationic complex of copper and adenine and hexafluorosilicate anions by a slow diffusion method and was demonstrated for trapping carbon dioxide in preference to methane and nitrogen. With one-dimensional pores of about 3.6 × 3.6 Å to induce their distinguishing interactions with the three components, SMOF-SIFSIX-1 exhibited excellent selective gas sorption behaviors for CO2/CH4 (50:50) and CO2/N2 (15:85) gas mixtures with ideal adsorbed solution theory selectivities of 21.1 and 131.7 at 273 K and 100 kPa pressure, respectively, outperforming most of reported hydrogen-bonded organic frameworks so far. Neutron powder diffraction and DFT-D calculations were also carried out to investigate the CO2 adsorption configuration on SMOF-SIFSIX-1a, which suggested that this framework catch CO2 due to “C···F” and “O···H” supramolecular interactions between CO2 molecules and SMOF-SIFSIX-1a. This study demonstrates that the rarely studied SMOF material shows promising potential in gas adsorption separation.

Solvent-dependent supramolecular self-assembly of boron cage pillared metal–organic frameworks for selective gas separation

A family of microporous boron cage pillared supramolecular metal–organic frameworks are synthesized with the self-assembly behavior controlled by solvents. Interpenetrated BSF-4 is potential for highly selective C2H2/C2H4 and C2H2/CO2 separation.

Supramolecular Fabrication of Complex 3D Hollow Polymeric Hydrogels with Shape and Function Diversity.

Inspired by the high importance of hollow structures in nature such as blood vessels and bamboos in matter transportation, properties enhancement, or even survival of living creatures, the creation of hollow materials remains of considerable interest. However, constructing hollow unique living-like soft and wet polymeric hydrogels with desirable structures and functionalities is still a big challenge. Here, we reported a robust and effective strategy to fabricate complex three-dimensional (3D) hollow polymeric hydrogel with designed shape and function diversity on the basis of supramolecular interactions. By placing a Ca2+ included gelatin core into the solution of alginate, hydrogel shell could be formed along with the shape of the gelatin core via coordination between alginate chains and Ca2+ diffused from gelatin. The hollow hydrogel could finally be obtained by dissolving the gelatin core. Various complex 3D hollow structures could be achieved by designing/constructing assembled gelatin core as a building block with adjustable supramolecular metal coordination position and strength. Moreover, hollow hydrogels with function diversity could be developed by introducing functional polymers or nanoparticles into the hydrogel wall. This work has made important progress in developing hollow polymeric hydrogel with desirable structures, shapes, and various functional applications including soft actuators and chemical reaction containers.

A Host-Guest Supercapacitor Electrode Material Based on a Mixed Hexa-Transition Metal Sandwiched Arsenotungstate Chain and Three-Dimensional Supramolecular Metal-Organic Networks with One-Dimensional Cavities.

The mixed hexa-transition metal (hexa-TM) sandwiched arsenotungstate derivative, [CuI3(pz)2(phen)3]2[CuI(phen)2][{Na(H2O)2}{(VIV5CuIIO6)(AsIIIW9O33)2}]·6H2O (1) (pz = pyrazine; phen = 1,10-phenanthroline), has been hydrothermally synthesized and structurally characterized. In compound 1, two {AsW9O33} clusters are connected by mixed hexa-TM ring unit {VVI5CuIIO6} to form a sandwich-type dimer, which are further bonded in "ABAB" mode by the {Na(H2O)2} linker resulting in pure inorganic chains. The unique "L-shaped" trinuclear complex {Cu3(phen)3(pz)2} is supported together via staggered π-π interactions to generate extending waveform two-dimensional supramolecular layers, which are further aggregated with their adjacent analogues by complexes {Cu(phen)2} via H-bonding interaction to yield an unprecedented three-dimensional (3D) metal-organic networks with one-dimensional (1D) cavities. The pure inorganic 1D sandwich chains are implanted in the cavities as guest units via supramolecular interactions to form a POMOF 3D framework. Compound 1, as the electrode of the supercapacitor, exhibits higher specific capacitances (825 F g-1 at a current density of 2.4 A g-1), better rate capability, more durable cyclic stability (91.4% of cycle efficiency after 3000 cycles), and improved conductivity and electroactivity compared to those of parent polyoxometalate (POM) Na9[AsW9O33]·19H2O (2) and 6-Cu-substituted POM [Cu6(imi)6{AsIIIW9O30Cl3}2]·6H2O (3), which may be attributed to the introduction of V4+, the unique host-guest structure, and the rich π electron system. In addition, compound 1 exhibits dual-function electrocatalytic behavior in reducing inorganic salt IO3- and oxidizing the organic molecule dopamine.

N-Doped Porous Carbon Derived by Direct Carbonization of Metal–Organic Complexes Crystal Materials for SO2 Adsorption

Three metal–organic complexes crystal materials (MOC-1, MOC-2, and MOC-3) have been hydrothermally synthesized. Driven by C–H···O and C–H···Cl hydrogen bonding interactions, MOC-1, MOC-2, and MOC-3 displayed supramolecular metal–organic frameworks with pcu, bnn, dia topology, respectively. Subsequently, N-doped porous carbons (NPCs) were obtained from carbonization of three metal–organic complexes (MOCs) crystal materials. The resulting NPCs were multiwalled graphite type structures, with high Brunauer, Emmett and Teller surface area (3186.5 m2 g–1), pore volume (2.16 cm3 g–1), and nitrogen content (19.6%), and the N atoms of the MOC precursors were mostly retained. Especially, benefiting from the largest surface area, micropore structure, more disordered stacks of carbon layers, and the largest displacement distance of D band and G band, NPCs showed a significant amount of SO2 adsorption capacity, up to 156.72 mg g–1. The SO2 adsorption capacity increased remarkably over 12 times with the addition of O2 and H2O together. Theoretical calculations indicated that N doping into N-doped porous carbons remodels the local electronic density as well as electrostatic surface potential, enhancing the SO2 adsorption. This work demonstrates a clear and significant advance for preparing N-doped porous carbon materials from MOCs for effective SO2 adsorption.

Super metal hydrogels constructed from a simple tripodal gelator and rare earth metal ions and its application in highly selective and ultrasensitive detection of histidine

A series of stable super metal hydrogels (TP-Ms, M = Tb3+, Eu3+, La3+ and Ce3+) with a low critical gelation concentration (2.28 × 10-3 M, 0.1%) was successfully constructed by forming hierarchical assemblies of a tripodal gelator (TP) with rare earth metal ions (Tb3+, Eu3+, La3+ and Ce3+). Interestingly, the super metal hydrogels TP-Eu and TP-La show a specific and ultrasensitive response to histidine (His). The addition of a series of amino acids into the metal hydrogels TP-Eu and TP-La showed that only His could induce distinct fluorescent enhancement for TP-Eu and TP-La, while other amino acids did not significantly interfere with the His sensing process. The LODs of super metal-hydrogel TP-Eu and TP-La for His are (1.83-1.94) × 10-9 and (1.83-1.85) × 10-9 M, respectively. In addition, constructing super supramolecular metal hydrogels by hierarchical assemblies of an easily synthesized tripodal gelator and rare earth metal ions is a novel and efficient approach to the design and development of multi-functional super supramolecular metal hydrogel-based materials.

Size-Selective Hydroformylation by a Rhodium Catalyst Confined in a Supramolecular Cage.

Size‐selective hydroformylation of terminal alkenes was attained upon embedding a rhodium bisphosphine complex in a supramolecular metal–organic cage that was formed by subcomponent self‐assembly. The catalyst was bound in the cage by a ligand‐template approach, in which pyridyl–zinc(II) porphyrin interactions led to high association constants (>105 m −1) for the binding of the ligands and the corresponding rhodium complex. DFT calculations confirm that the second coordination sphere forces the encapsulated active species to adopt the ee coordination geometry (i.e., both phosphine ligands in equatorial positions), in line with in situ high‐pressure IR studies of the host–guest complex. The window aperture of the cage decreases slightly upon binding the catalyst. As a result, the diffusion of larger substrates into the cage is slower compared to that of smaller substrates. Consequently, the encapsulated rhodium catalyst displays substrate selectivity, converting smaller substrates faster to the corresponding aldehydes. This selectivity bears a resemblance to an effect observed in nature, where enzymes are able to discriminate between substrates based on shape and size by embedding the active site deep inside the hydrophobic pocket of a bulky protein structure.

Directed Self-Assembly of Trimeric DNA-Bindingchiral Miniprotein Helicates.

We propose that peptides are highly versatile platforms for the precise design of supramolecular metal architectures, and particularly, for the controlled assembly of helicates. In this context, we show that the bacteriophage T4 Fibritin foldon (T4Ff) can been engineered on its N-terminus with metal-chelating 2,2′-bipyridine units that stereoselectively assemble in the presence of Fe(II) into parallel, three-stranded peptide helicates with preferred helical orientation. Modeling studies support the proposed self-assembly and the stability of the final helicate. Furthermore, we show that these designed mini-metalloproteins selectively recognize three-way DNA junctions over double-stranded DNA.

Supramolecular metal–organic frameworks based on neutral and cationic copper(II) α-hydroxycarboxylate complexes with 2,2′-dipyridylamine

The reaction of CuCO3·Cu(OH)₂ with three different α-hydroxyacids (H2L′) and the nitrogen donor coligand 2,2′-dipyridylamine (dipyam) has produced five new discrete copper(II) complexes. Two kind of compounds have been isolated: neutral complexes of formula [Cu(H2L′)2(dipyam)] and cationic [Cu(H2L′)(dipyam)2](H2L′) complexes. Four of these compounds have been studied by single-crystal X-ray diffraction and the analysis of their molecular crystal structures were also performed by the analysis of their Hirshfeld surfaces. The thermal behaviour has also been investigated.

Double role of metalloporphyrins in catalytic bioinspired supramolecular metal-organic frameworks (SMOFs).

Heterogeneous catalysts are of great interest in many industrial processes for environmental reasons and, during recent years, a great effort has been devoted to obtain metal-organic frameworks (MOFs) with improved catalytic behaviour. Few supramolecular metal-organic frameworks (SMOFs) are stable under ambient conditions and those with anchored catalysts exhibit favourable properties. However, this paper presents an innovative approach that consists of using metal nodes as both structural synthons and catalysts. Regarding the latter, metalloporphyrins are suitable candidates to play both roles simultaneously. In fact, there are a number of papers that report coordination compounds based on metalloporphyrins exhibiting these features. Thus, the aim of this bioinspired work was to obtain stable SMOFs (at room temperature) based on metallo-porphyrins and explore their catalytic activity. This work reports the environmentally friendly microwave-assisted synthesis and characterization of the compound [H(bipy)]2[(MnTPPS)(H2O)2]·2bipy·14H2O (TPPS = meso-tetra-phenyl-porphine-4,4',4'',4'''-tetra-sulfonic acid and bipy = 4,4'-bi-pyridine). This compound is the first example of an MnTPPS-based SMOF, as far as we are aware, and has been structurally and thermally characterized through single-crystal X-ray diffraction, IR spectroscopy, thermogravimetry and transmission electron microscopy. Additionally, this work explores not only the catalytic activity of this compound but also of the compounds μ-O-[FeTCPP]2·16DMF and [CoTPPS0.5(bipy)(H2O)2]·6H2O. The structural features of these supra-molecular materials, with accessible networks and high thermal stability, are responsible for their excellent behaviour as heterogeneous catalysts for different oxidation, condensation (aldol and Knoevenagel) and one-pot cascade reactions.

(3,3)-Connected Three-dimentional Supramolecular Metal Organic Polyhedral Based on Nanometresized Ligand with Magnetism Properties

A three-dimentinal metal organic framework [Co2(L)Cl(DMF)2(H2O)](DMF)3(H2O)3 based on the nano-metresized ligand 4,4′,4″-[1,3,5-benzenetriyltris(carbonylimino)]trisbenzoic acid was synthesized, and characterized by means of single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy, thermogravimetry analysis and magnetism. This obtained structure can be considered to be constructed from 2D layer, which displays the topology of hbc based on Co2(COO)3 secondary building unit, and further to be linked into a 3D supramolecular architecture by N—H···O hydrogen bonds. The magnetism of the complex was carried out, which shows ferromagnetic exchange interactions.

Porous Supramolecular Architectures Based on π-Stacking Interactions between Discrete Metal-Adenine Entities and the Non-DNA Theobromine/Caffeine Nucleobases

This work is aimed at the analysis of the π–π stacking interactions as the driving force to develop porous supramolecular metal–organic frameworks (SMOFs) as an alternative to more directional hydrogen bonding interactions. Four compounds based on the interaction between rigid copper/adenine entities and theobromine/caffeine molecules have been synthesized: [Cu7(μ-ade)6(μ3-OH)6(μ-H2O)6](theo)2·∼28H2O (1), [Cu2(μ-ade)4(H2O)2]·3Htheo·∼7H2O (2), [Cu2(μ-ade)4(H2O)2]·2Htheo·∼18H2O (3), and [Cu2(μ-ade)4(H2O)2]·(caf)·∼6H2O (4). The blue compound 1 is formed by wheel-shaped cationic heptameric units where the copper atoms are bridged by hydroxide anions, water molecules, and adeninato ligands with a μ-κN3:κN9 coordination mode. The assembly of the heptameric entities and the theobrominate anions takes place mainly through π–π stacking interactions involving the adeninato ligands and theobrominate moieties. Although compound 1 exhibits an open-framework with voids representing 37% of the unit cell, the plasticity ...

Hierarchically Structured Self‐Healing Sensors with Tunable Positive/Negative Piezoresistivity

AbstractIt is a challenge to manufacture flexible sensors that possess easily distinguishable biomotion signals, strong response reliability, and excellent self‐healing capability. Herein, a self‐healing sensor with tunable positive/negative piezoresistivity is designed by the construction of hierarchical structure connected through supramolecular metal–ligand coordination bonds. The developed sensors can be integrated with the human body to detect multiple tiny signals, such as pronunciation, coughing, and deep breathing. Interestingly, the nanostructured elastomer sensor with and without a flexible yarn electrode shows negative and positive current signals, respectively, making it easy to be identify. Furthermore, it exhibits very fast (2 min), autonomous, and repeatable self‐healing ability with high‐healing efficiency (88.6% after the third healing process). The healed samples still possess flexibility, high sensitivity, and accurate detection capability, even after bending over 10 000 cycles. The excellent biomimetic self‐healing performance combined with the tunable piezoresistivity make it promising for next‐generation wearable electronics.

Providing evidence for the requirements to achieve supramolecular materials based on metal–nucleobase entities

This article evaluates the strategy to design supramolecular metal–organic frameworks using metal–nucleobase entities as building units.

Research on the Mechanism of Aggregation-Induced Emission through Supramolecular Metal-Organic Frameworks with Mechanoluminescent Properties and Application in Press-Jet Printing.

This study investigates the mechanism of AIE in the solid state through supramolecular metal-organic frameworks and mechanoluminescent materials for the first time. Herein, four novel differently substituted Schiff base building blocks, SB1-SB4, exhibit typical AIE properties with various fluorescence emissions from yellow to green. SB1-SB4 are linked through C-H···O hydrogen bonding interactions to construct supramolecular metal-organic frameworks (SMOFs): namely, SMOFSB1-SMOFSB4. Particularly, among these SMOFs, SMOFSB3 is observed to have micropores in the 3D supramolecular structure and exhibits mechanoluminescent properties (grinding). An emission turn-on mechanism occurs with destruction of micropores by grinding and blockage of intramolecular rotations of the methyl and acetonitrile in the micropores, resulting in emission turn-on in SMOFSB3. Single-crystal X-ray structures, powder X-ray diffraction, emission spectra at room temperature, temperature-dependent emission spectra, DFT calculations, and a charge separation hypothesis well demonstrate the emission turn-on mechanism, which is consistent with the mechanism of AIE. More importantly, the molecules demonstrated potential application for press-jet printing.

23 ツユクサ青色花弁色素コンメリニンの構成成分フラボコンメリンの合成と色発現機構(口頭発表の部)

23 ツユクサ青色花弁色素コンメリニンの構成成分フラボコンメリンの合成と色発現機構(口頭発表の部)

Encapsulation and Sensitization of Ln3+ within Indium Metal–Organic Frameworks for Ratiometric Eu3+ Sensing and Linear Dependence of White-Light Emission

Four novel compounds {[In(FDA)(HFDA)(H2O)4]·2H2O} (In1) and {[Ln2(FDA)2(H2O)10]·FDA·6H2O}n (Ln = Dy2, Eu3, Gd4) have been hydrothermally synthesized by using the ligand furan-2,5-dicarboxylic acid (H2FDA). Driven by hydrogen bonding and π···π stacking, In1 displays a supramolecular metal–organic framework (MOF) with 6-connected pcu topology. Isostructural Dy2, Eu3, and Gd4 possess one-dimensional “wave-like” chains and further exhibit bnn topological structures with the Schlafli symbol of (46·64) via a hydrogen bonding network. The triplet state (T1 = 22371 cm–1) of H2FAD studied by compound Gd4 indicates that the energy transition from the H2FDA ligand to the Eu3+ ion in compound Eu3 is efficient but inefficient to the Dy3+ ion in compound Dy2. Interestingly, the uncoordinated carbonyl group of compound In1 can sensitize Ln3+ ions to obtain Dy3+@In1 and Eu3+@In1 materials for enhancing luminescence. The possible sensitization mechanism is studied by X-ray photoelectron spectroscopy and surface photovolta...

Supramolecular Metal Arraying in Porphyrin/Phthalocyanine Conjugates for Catalytic Applications

Recently, we reported synthesis of porphyrin/phthalocyanine conjugates linked by fourfold rotaxane. In the conjugate, a porphyrin and a phthalocyanine formed a heterodimer in a cofacial fashion (Fig. 1a). [1] The conjugate is a promising platform for supramolecular catalysts based on dinuclear porphyrinoid complexes, because various metal ions to be a functional center are able to be arrayed in the conjugate regioselectively to afford homo- and hetero-dinuclear centers in the conjugate. [2,3] Moreover, these arrays were expanded to hetero-trinuclear arrays (Fig. 1b). [3-6] In this paper, we will present regioselective metal arraying in the conjugate and the supramolecular catalytic functions (Fig. 2). One of the methods to prepare the hetero-dinuclear complexes was to use the difference of metalation rate between porphyrin and phthalocyanine. We found reaction conditions for porphyrin-selective Fe(II) or Ni(II) insertion and phthalocyanine-selective Mn(II) insertion. Subsequent metalation to another porphyrinoid in the conjugate gave a hetero-dinuclear complex. We used these multinuclear complexes in the conjugate as catalysts. The dinuclear iron complex exhibited good catalytic activity in electrochemical reduction of molecular oxygen to water. [7]