Supramolecular Cation Research Articles

Epoxidation of Olefins Catalyzed by Sulfate‐based Supramolecular Ion Pairs

AbstractThe development of inexpensive and effective catalysts for the epoxidation of olefins to epoxides, which are key commodities for the chemical industry, is a continuing challenge. In this context, we present a supramolecular solution with the development of new host‐guest assemblies of sulfate ions and amidoammonium receptor cations that, for the first time, are shown to act as catalysts for olefin epoxidation by hydrogen peroxide under biphasic conditions. Analysis of the reaction mechanism shows that the reactive and oxidizing peroxymonosulfate is formed in the organic phase. Furthermore, a variety of readily available precursors may be used to form the supramolecular ion pairs (SIPs), which is enabling a large‐scale synthesis of the catalysts while maintaining catalytic control and effectiveness.

Supramolecular pyrrole radical cations for bacterial theranostics.

Bacterial infections with emerging resistance to antibiotics require urgent development of antibacterial agents with new core skeletons. Recently, a series of antibacterial agents have been reported based on positively charged organic groups, such as ammonium, guanidine, and phosphonium groups, which can selectively bind and destroy negatively charged bacterial membranes. To achieve imaging-guided precise antibacterial therapy, these positively charged organic groups usually require further decoration with imaging modalities, such as fluorescence. However, most fluorophores with electron-closed shell structures usually suffer from tedious synthetic procedures for preparation. We herein prepare a series of positively charged and deep-red fluorescent supramolecular pyrrole radical cations (P˙+-CB[7]) based on the simple mixing of pyrroles and CB[7] in water under air. The readily available deep-red fluorescent P˙+-CB[7] can not only be used for selective imaging and killing of live Gram-positive bacteria with excellent biocompatibility, but also for imaging of dead Gram-negative bacteria killed by drugs and in vivo monitoring of phagocytosis of bacteria by innate immune cells in zebrafish. It is believed that the deep-red fluorescent pyrrole radical cations as a new core skeleton are promising in bacterial theranostics.

Features of adsorption phenomena in strontium salt solutions in the presence of some cavitands of cucurbituril family

The influence of the electrolyte nature and cation charge on the adsorption properties of cucurbit[6]uril supramolecular complexes are established and discussed. The results show the narrowing of the adsorption potential region of these complexes with increasing cation charge, and the possibility to form an adsorbate layer of supramolecular cations associated with surface-active electrolyte anions at the positive boundary of the adsorption potential region.

Multifunctional Triggering by Solid-Phase Molecular Motion: Relaxor Ferroelectricity, Modulation of Magnetic Exchange Interactions, and Enhancement of Negative Thermal Expansion

Although the development of artificial molecular machines has garnered considerable attention in recent years, the construction of multifunctional solid-state molecular machines still faces several challenges. Herein, we report a supramolecular approach as an efficient strategy for building multifunctional trigger systems. In crystals composed of [Ni(dmit)2]− with a spin of S = 1/2 and supramolecular structures consisting of 4-aminopyridinium+ and benzo[18]crown-6, supramolecular cations with dynamic degrees of freedom affect the magnetic and dielectric properties and induce negative thermal expansion (NTE). The supramolecular cations in the crystals form one-dimensional columns. Two adjacent columns form a supramolecular ladder structure via π···π interactions between the phenylene groups of benzo[18]crown-6 and are arranged within a two-dimensional layer. A disorder between the two sites of the phenylene ring was observed in one of the crystallographically independent benzo[18]crown-6. Disordered benzo[18]crown-6 formed polar domains within the crystal, resulting in relaxor ferroelectricity. With increasing temperature, the supramolecular ladders elongated and the translational motion of benzo[18]crown-6 caused the molecular ladder to move closer to each other. Consequently, the crystals shrunk in the direction perpendicular to the ladder, exhibiting uniaxial NTE, and the magnetic exchange interaction between the [Ni(dmit)2]− crystals was disrupted.

Cucurbit[10]uril-based supramolecular radicals: Powerful arms to kill facultative anaerobic bacteria.

Two water-soluble supramolecular complexes (CB[10]⊃PSA and CB[10]⊃TPE-cyc) are constructed based on the host-guest interaction between cucurbit[10]uril (CB[10]) and perylene diimide derivative (PSA) or tetracationic cyclophane (TPE-cyc). Attributing to the matched redox potential, both supramolecular complexes can be specifically reduced into corresponding supramolecular radical cations or anions by facultative anaerobic E. coli. Benefiting from the strong near-infrared (NIR) absorption, CB[10]⊃PSA radical anions and CB[10]⊃TPE-cyc radical cations act as efficient NIR photosensitizers and perform an excellent antimicrobial activity (close to 100%) via PTT. In addition, the biocompatibility of TPE-cyc is notably improved under the protection of CB[10], guaranteeing its biosafety for in vivo application. CB[10]⊃PSA radical anions and CB[10]⊃TPE-cyc radical cations are in situ generated in the E. coli-infected abscess of mice and effectively inhibit the bacterial infection without obvious system toxicity. It is anticipated that this supramolecular strategy may pave a new way for the selective bacteria inhibition to regulate the balance of different bacterial flora.

Uniaxial negative thermal expansion induced by molecular rotation in a one-dimensional supramolecular assembly with associated peculiar magnetic behavior

An alternative approach for achieving negative thermal expansion (NTE) in a molecular crystal of [Ni(dmit)2]− salt with supramolecular cation composed of pyridazinium and dibenzo[24]crown-8. Deformation of supramolecular cation induces NTE and peculiar magnetic responses.

A crown ether supramolecular host-guest complex with Keggin polyoxometalate: Synthesis, crystal structure and electrocatalytic performance for hydrogen evolution reaction

A new crown ether–polyoxometalate assembly [K(H24C12O6)]3[K(H24C12O6)(CH3CN)][SiMo12O40] (1) based on the Keggin-type polyanion [SiMo12O40]4− was successfully synthesized through one-pot strategy in acetonitrile solution. The polyanion is coordinated to two [K([18]-crown-6)]+ supramolecular cations via crown–K–O(POM) coordinate-covalent bonds, leading to the formation of a spindle-shaped discrete structure. Complex 1 exhibited good hydrogen evolution reaction (HER) activity in an acidic medium. Moreover, a small overpotential η10 of 120 mV and a Tafel slope of 112 mV dec−1 were obtained. This crown ether–polyoxometalate hybrid electrocatalyst also presented excellent HER stability even after 2000 cycles of operation.

Fluoride-bridged dinuclear dysprosium complex showing single-molecule magnetic behavior: supramolecular approach to isolate magnetic molecules.

Using Na-encapsulated benzo[18]crown-6 (Na)(B18C6) as a counter cation, we successfully magnetically isolated a fluoride-bridging Dy dinuclear complex {[(PW11O39)Dy(H2O)2]2F} (Dy2POM) with lacunary Keggin ligands. (Na)(B18C6) formed two types of tetramers through C–H⋯O, π⋯π and C–H⋯π interactions, and each tetramer aligned in one dimension along the c-axis to form two types of channels. One channel was partially penetrated by a supramolecular cation from the ±a-axis direction, dividing the channel in the form of a “bamboo node”. Dy2POM was spatially divided by this “bamboo node,” which magnetically isolated one portion from the other. The temperature dependence of the magnetic susceptibility indicated a weak ferromagnetic interaction between the Dy ions bridged by fluoride. Dy2POM exhibited the magnetic relaxation characteristics of a single-molecule magnet, including the dependence of AC magnetic susceptibility on temperature and frequency. Magnetic relaxation can be described by the combination of thermally active Orbach and temperature-independent quantum tunneling processes. The application of a static magnetic field effectively suppressed the relaxation due to quantum tunneling.

Molecular motion of halogenated ethylammonium/[18]crown-6 supramolecular ions in nickel dithiolate magnetic crystals

Supramolecular cations, consisting of ethylammonium derivatives (X–CH2CH2–NH3+) complexed with [18]crown-6, were incorporated into [Ni(dmit)2]− crystals in order to promote molecular motion.

Dynamic Molecular Behavior and Physical Properties of Molecular Ionic Crystals with Supramolecular Cation Structure

Dynamic Molecular Behavior and Physical Properties of Molecular Ionic Crystals with Supramolecular Cation Structure

Synthesis, Structure, and Dielectric Properties of (3-Nitroanilinium) (18-Crown) (PF6)

(3-Nitroanilinium) (18-crown) (PF6) (1), which is an organic-inorganic hybrid containing one-dimensional chains of hydrogen-bonded supramolecular cations, was synthesized under slow evaporation conditions and subjected to differential scanning calorimetry, temperature-dependent dielectric measurements, and variable-temperature single-crystal X-ray diffraction analysis. These analyses revealed the occurrence of a reversible structural phase transition [P21/n P21/c] at 223 K and a dielectric anomaly, which, based on the results of structural analysis and potential energy calculations, was attributed to the synergistic effect between the pendulum-like motion of the nitro group in the supramolecular cation, (3-nitroanilinium)(18-crown), and the order-disorder motion of PF6− anions.

Dynamics and Structural Diversity of Li+(Crown Ether) Supramolecular Cations in Electrically Conducting Salts

Li+([12]crown-4)2(TCNQ)2 (1), Li+([15]crown-5)(TCNQ)2 (2a and 2b), and Li+([18]crown-6)(TCNQ)2·(H2O)2 (3) salts (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane) were prepared and examined in terms of c...

Stable Ferromagnetic Crystal of Two‐Dimensional Manganese‐Chromium Oxalate with Supramolecular Cation

A supramolecular cation of (m‐FAni+)(tst‐DCH[18]crown‐6), where m‐FAni+ and tst‐DCH[18]crown‐6 denote m‐fluoroanilinium and trans‐syn‐trans‐dicyclohexano[18]crown‐6, respectively, was introduced into a ferromagnetic {[MnIICrIII(oxalate)3]–} layer to obtain a stable organic‐inorganic hybridized crystal. The crystal structure of (m‐FAni+)(tst‐DCH[18]crown‐6){[MnIICrIII(oxalate)3]–} was constructed by alternate stacking of a two‐dimensional honeycomb layer of {[MnIICrIII(oxalate)3]–} and the supramolecular cations. Cyclohexyl moieties of tst‐DCH[18]crown‐6 penetrated the pores of the honeycomb layers, excluding solvent molecules in the crystal. The anionic layers showed ferromagnetic order of MnII and CrIII ions with S = 5/2 and S = 3/2 spins, respectively, at 5.5 K. Although the m‐FAni+ showed disorder with respect to 180° rotation of the aryl ring, no significant anomaly was observed in the dielectric response, suggesting that the disorder is static.

Structural Modulation of Electrically Conducting TCNQ Salts Using Na+(crown ether) Supramolecular Cations

The single crystals of Na+([12]crown-4)2(TCNQ)2 (1), Na+([15]crown-5)(TCNQ)2 (2), Na+([18]crown-6)(TCNQ)2.5 (3), and Na+([24]crown-8)(TCNQ)2 (4) (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane) were prepared and defined by single-crystal X-ray structural analyses. Of these, salts 1 and 2 showed structural phase transitions at 320 and 185 K, respectively, upon heating. According to differential scanning calorimetry, temperature (T)-dependent crystal structures, and dielectric measurements, the motional freedom and orientation change of the spherical sandwich-type Na+([12]crown-4)2 supramolecular cation activated the phase transition. Furthermore, a symmetry change in salt 2 from the low-T Pc to the high-T P21/c was observed and a symmetry change in the Na+···NC– coordination environment is the origin of the structural phase transition at 185.4 K. Conversely, no distinct structural phase transitions were observed for salts 3 and 4. In all of the crystals, the π dimer of the partially reduced TCNQ formed a segregated π-stacking structure that interacted further by interdimer interactions to form electrically conducting TCNQ layers. Nonuniform and one-dimensional (1D) π-stacking columns of TCNQ were observed in salts 1, 3, and 4, while two-dimensional (2D) spanning-overlap interdimer interactions were confirmed in salt 2. The electrical resistivity and activation energy of 2D salt 2 were 10–10000 and 2 times lower, respectively, than those of the 1D electronic systems of salts 1, 3, and 4.

Magnetic Switching by Desorption/Adsorption of an Organic Solvent Molecule from/on [Ni(dmit)2]− Salt

Herein, the synthesis and physical properties of a monovalent [Ni(dmit)2]− salt (dmit2− = 2-thioxo-1,3-dithiole-4,5-dithiolate) containing a supramolecular cation composed of Na+ ions, dibenzo[18]c...

MnIII-FeIII Heterometallic Compounds within Hydrogen-Bonded Supramolecular Networks Promoted by an [Fe(CN)5(CNH)]2- Building Block: Structural and Magnetic Properties.

The reaction of [Fe(CN)6]3- and [Mn(acacen)]+ (H2acacen = N, N'-bis(acetylacetone)ethylenediamine) building units in the presence of supramolecular cations, [(F-Anil)(18-crown-6)]+ (F-Anil+ = 3-fluoroanilinium) or [(Me-F-Anil)(18-crown-6)]+ (Me-F-Anil+ = 3-fluoro-4-methylanilinium), affords two new bimetallic compounds, [(F-Anil)(18-crown-6)][Mn(acacen)Fe(CN)5(CNH)]·MeOH (1) and [(Me-F-Anil)(18-crown-6)][Mn(acacen)(MeOH)Fe(CN)5(CNH)]·MeOH (2), respectively. Compound 1 exhibits a one-dimensional topology, while compound 2 is a dinuclear discrete system due to the coordination of a MeOH molecule at the axial position of the [Mn(acacen)]- unit. For both systems, the acidity of the corresponding supramolecular cation triggers the protonation of the FeIII moiety as [Fe(CN)5(CNH)]2-. Moreover, the resulting -CNH ligand induces hydrogen bonding interactions connecting the chains for 1 or the molecules for 2 into higher dimensional supramolecular networks. Magnetic properties of compounds incorporating these [Fe(CN)5(CNH)]2- building blocks were, for the first time, thoroughly investigated, indicating a three-dimensional antiferromagnetic order of single-chain magnets for 1 and an antiferromagnetically interacting S = 3/2 spin ground state for 2.

Anisotropic dielectric phase transition triggered by pendulum-like motion coupled with proton transfer in a layered hybrid crystalline material (4-nitroanilinium+) (18-crown-6) (H2PO4−) (H3PO4)2

The organic–inorganic hybrid phase-transition material, (4-nitroanilinium+) (18-crown-6) (H2PO4−) (H3PO4)2 (1), was successfully synthesized. The organic (4-nitroanilinium) (18-crown-6)+ supramolecular cation layer and inorganic phosphate anion layer were arranged alternately. Differential scanning calorimetry (DSC), temperature-dependent dielectric measurements, and variable-temperature single-crystal X-ray diffraction analysis confirmed the reversible isostructural phase transition of 1 with the same space group Pbca at 225 K, wherein the synergistic effect between the pendulum-like motion of organic cations and the proton transfer in the OH⋯O hydrogen bonding of inorganic anions was mainly responsible for the phase-transition behavior of 1. The most striking dielectric property was the remarkable anisotropy along various crystallographic axes. A potential-energy calculation further supported the possibility of dynamic motion of cations in the crystal.

Two Supramolecular Inorganic–Organic Hybrid Crystals Based on Keggin Polyoxometalates and Crown Ethers

New supramolecular structures were designed in this work using large-sized polyoxometalates (POMs) and crown-ether-based supramolecular cations selected as building blocks. Two novel supramolecular inorganic–organic hybrids [(3-F-4-MeAnis)([18]crown-6)]2[SMo12O40]•CH3CN (1) and [(4-IAnis)([18]crown-6)]3[PMo12O40]•4CH3CN (2) (3-F-4-MeAnis = 3-fluoro-4-methylanilinium and 4-IAnis = 4-iodoanilinium) were synthesized. Crystals 1 and 2 have been characterized by infrared spectroscopy (IR) and elemental analysis (EA). Based on X-ray diffraction analysis, Crystals 1 and 2 were constructed through noncovalent bonding interactions and belong to different space groups due to the difference of the building blocks used. Supramolecular cations formed due to strong N–H···O hydrogen bonding interactions between the six oxygen atoms of [18]crown-6 molecules and nitrogen atoms of anilinium derivatives. Crystal 1 has two different supramolecular cations with an anti-paralleled arrangement that forms a dimer through weak hydrogen bonding interactions between adjacent [18]crown-6 molecules. Crystal 2 has three independent supramolecular cations that fill large spaces between the [PMo12O40] polyoxoanions forming a rhombus-shape packing arrangement in the ac plane. Crystals 1 and 2 are unstable at room temperature.

A supramolecular radical cation: folding-enhanced electrostatic effect for promoting radical-mediated oxidation.

We report a supramolecular strategy to promote radical-mediated Fenton oxidation by the rational design of a folded host-guest complex based on cucurbit[8]uril (CB[8]). In the supramolecular complex between CB[8] and a derivative of 1,4-diketopyrrolo[3,4-c]pyrrole (DPP), the carbonyl groups of CB[8] and the DPP moiety are brought together through the formation of a folded conformation. In this way, the electrostatic effect of the carbonyl groups of CB[8] is fully applied to highly improve the reactivity of the DPP radical cation, which is the key intermediate of Fenton oxidation. As a result, the Fenton oxidation is extraordinarily accelerated by over 100 times. It is anticipated that this strategy could be applied to other radical reactions and enrich the field of supramolecular radical chemistry in radical polymerization, photocatalysis, and organic radical battery and holds potential in supramolecular catalysis and biocatalysis.

Supramolecular self-assembly for designing non-centrosymmetric crystals based on Keggin polyoxometallates and crown ether

We report the synthesis of five novel crystals [(4-BrAni+)(DB[18]crown-6)]2[SMo12O402-]·2CH3CN (1), [(4-BrAni+)(B[18]crown-6)]2[SMo12O402-]·CH3CN (2), [(4-BrAni+)(B[18]crown-6)]3[PMo12O402-]·2CH3CN (3), [(3-AP+)3(B[18]crown-6)2][PMo12O403-] (4) and [NBu4+][(3-AP2+)(DB[30]crown-10)][PMo12O403-]·CH3CN (5) (4-BrAni+ = 4-bromoanilinium; B[18]crown-6 = benzo[18]-crown-6; DB[18]crown-6 = dibenzo[18]-crown-6; DB[30]crown-10 = dibenzo[30]-crown-10; 3-AP+ = 3-aminopyridinium; 3-AP2+ = 3-ammoniumpyridinium; NBu4+ = tetrabutylammonium). In order to construct non-centrosymmetric crystals, the five crystals were designed using a method to gradually introduce asymmetry into the building units. Crystal 1 was constructed with a symmetric supramolecular cation (SPC) [(4-BrAni+)(DB[18]crown-6)], resulting in a P21/n space group. The asymmetric SPC [(4-BrAni+)(B[18]crown-6)] was introduced into [SMo12O402-] to obtain crystal 2, which belongs to the symmetric P1[combining macron] space group. Introducing trivalent [PMo12O403-], [(4-BrAni+)(B[18]crown-6)] produced crystal 3 with a non-centrosymmetric Pc space group. The asymmetric sandwich SPC [(3-AP+)3(B[18]crown-6)2] was designed with multiple hydrogen bonding sites on the 3-AP+ cation, and crystal 4 was obtained with trivalent [PMo12O403-]. Crystal 4 has the properties of the chiral P1 space group. The distorted SPC (3-AP2+)(DB[30]crown-10) was constructed using flexible DB[30]crown-10, resulting in crystal 5 which matched the chiral P21 space group with trivalent [PMo12O403-]. This work focuses on strategies for the rational design of novel non-centrosymmetric crystals without a chiral synthon.