Supramolecular Boxes Research Articles

Guest-adaptive chiral coassembly of a conformationally locked host into supramolecular boxes and ladders through arene-perfluoroarene force

Guest-adaptive chiral coassembly of a conformationally locked host into supramolecular boxes and ladders through arene-perfluoroarene force

Synthesis, crystal structure and coordination behaviors of two unexpected tetranuclear Zn(II) and Co(II) supramolecular boxes derived from structural variation of coumarin schiff base ligand

Two unexpected tetranuclear supramolecular boxes, [Zn4(L')4(CH3OH)2]·2CH3OH (1) and [Co4(L)2(L')2(CH3OH)2]·acetone (2), with M4(μ3-O)2(μ2-O)4 core were obtained through reacting coumarin Schiff base H2L (H2L = 4-hydroxy-3-((2-hydroxyphenyl-imino)-methyl)-2hchrome-2-one) with Zn(OAc)2·4H2O and Co(OAc)2·4H2O, respectively. Interestingly, the original ligand (H2L) has changed into a new structure (H2L') in the process of forming single crystals. The structures of 1 and 2 were characterized by X-ray single crystal diffraction. 1 and 2 are tetranuclear structures including four metal centers (Zn(II) or Co(II)), four completely deprotonated ligands (four new (L')2- in 1, two original (L)2- and two new (L')2- in 2), two coordinated methanol molecules and several crystalline solvent molecules. Significantly, due to the action of Zn(II) and Co(II), the original Schiff base H2L completely changed from coumarin skeleton to quinoline skeleton to form a new ligand (H2L') in 1, while in 2 half of the ligands H2L involved in coordination changed to H2L' configuration, the other half maintained the original structure. In 1, Zn1 ions are six-coordinate octahedral configuration and Zn2 are five-coordinate distorted square-pyramidal configuration with τ = 0.38. In 2, Co1 are six-coordinate octahedral configuration and Co2 are five-coordinate triangular bipyramidal configuration with τ = 0.66.

PH-Responsive Pillar[6]arene-based Water-Soluble Supramolecular Hexagonal Boxes.

We describe the preparation of the first water-soluble pH-responsive supramolecular hexagonal boxes (SHBs) based on multiple charge-assisted hydrogen bonds between peramino-pillar[6]arenes 2 with the molecular "lid" mellitic acid (1 a). The interaction between 2 and 1 a, as well as the other "lids" pyromellitic and trimesic acids (1 b and 1 c, respecively) were studied by a combination of experimental and computational methods. Interestingly, the addition of 1 a to the complexes of the protonated form of pillar[6]arene 2, that is, 3, with bis-sulfonate 4 a or 4 b, immediately led to guest escape along with the formation of closed 1 a2 2 supramolecular boxes. Moreover, the process of the openning and closing of the supramolecular boxes along with threading and escaping of the guests, respectively, was found to be reversible and pH-responsive. This study paves the way for the easy and modular preparation of different SHBs that may have myriad applications.

PH‐Responsive Pillar[6]arene‐based Water‐Soluble Supramolecular Hexagonal Boxes

AbstractWe describe the preparation of the first water‐soluble pH‐responsive supramolecular hexagonal boxes (SHBs) based on multiple charge‐assisted hydrogen bonds between peramino‐pillar[6]arenes 2 with the molecular “lid” mellitic acid (1 a). The interaction between 2 and 1 a, as well as the other “lids” pyromellitic and trimesic acids (1 b and 1 c, respecively) were studied by a combination of experimental and computational methods. Interestingly, the addition of 1 a to the complexes of the protonated form of pillar[6]arene 2, that is, 3, with bis‐sulfonate 4 a or 4 b, immediately led to guest escape along with the formation of closed 1 a22 supramolecular boxes. Moreover, the process of the openning and closing of the supramolecular boxes along with threading and escaping of the guests, respectively, was found to be reversible and pH‐responsive. This study paves the way for the easy and modular preparation of different SHBs that may have myriad applications.

A Metal–Organic Supramolecular Box as a Universal Reservoir of UV, WL, and NIR Light for Long‐Persistent Luminescence

AbstractLong persistent luminescence (LPL) materials have a unique photophysical mechanism to store light radiation energy for subsequent release. However, in comparison to the common UV source, white‐light (WL) and near‐infrared (NIR) excited LPL is scarce. Herein we report a metal–organic supramolecular box based on a D–π–A‐type ligand. Owing to the integrated one‐photon absorption (OPA) and two‐photon absorption (TPA) attributes of the ligand, the heavy‐atom effect of the metal center, as well as π‐stacking and J‐aggregation states in the supramolecular assembly, LPL can be triggered by all wavebands from the UV to the NIR region. This novel designed supramolecular kit to afford LPL by both OPA and TPA pathways provides potential applications in anti‐counterfeiting, camouflaging, decorating, and displaying, among others.

A Metal-Organic Supramolecular Box as a Universal Reservoir of UV, WL, and NIR Light for Long-Persistent Luminescence.

Long persistent luminescence (LPL) materials have a unique photophysical mechanism to store light radiation energy for subsequent release. However, in comparison to the common UV source, white-light (WL) and near-infrared (NIR) excited LPL is scarce. Herein we report a metal-organic supramolecular box based on a D-π-A-type ligand. Owing to the integrated one-photon absorption (OPA) and two-photon absorption (TPA) attributes of the ligand, the heavy-atom effect of the metal center, as well as π-stacking and J-aggregation states in the supramolecular assembly, LPL can be triggered by all wavebands from the UV to the NIR region. This novel designed supramolecular kit to afford LPL by both OPA and TPA pathways provides potential applications in anti-counterfeiting, camouflaging, decorating, and displaying, among others.

2+2] Halogen-bonded boxes employing azobenzenes.

Herein, we report the synthesis and crystal structures of three [2+2] supramolecular boxes assembled by halogen bonding. The discrete, two-dimensional boxes with a length of 25-30 Å are based on rigid u-shaped halogen acceptors paired with highly fluorinated, azobenzenes bearing halogen bond donors.

Face-to-face stacking of caffeinium and [PMVI12O40]3− ions: A synthon for crystal engineering with purine bases

Ionic polyoxometales (Hcaf)3[PM12O40]·6H2O [M = Mo, W; caf = caffeine] exhibit unusual supramolecular structure dominated by multiple anion-π interactions, which occur at both axial sides of the caffeinium cations. These cations, when stacked to every of six square faces of POM cuboctahedra, afford supramolecular boxes and the resulting non-covalent cubic framework (α-Po topology) is generated by face-sharing of the boxes.

Alkali-metal-ion-directed self-assembly of redox-active manganese(III) supramolecular boxes.

The ability to organize functional molecules into higher dimensional arrays with well-defined spatial relationships between the components is one of the major goals in supramolecular chemistry. We report here a new route for the preparation of supramolecular boxes, incorporating two types of metal ions: (i) alkali-metal ions, which induce the supramolecular architecture and essentially play a structural role in the final compounds; (ii) manganese(III) ions, which are redox-active systems and give functionality to the new cages. Our results evidence that the size of the cavity inside the box can be tuned depending on the alkali metal used, a characteristic that gives this new family of compounds the potential to act selectively against different substrates. These compounds behave as active catalysts for disproportionation of H2O2 or for water photolysis, but they catalyze neither catecholase reaction nor peroxidase action upon using bulky organic substrates.

Dual templated synthesis of silver acetylide cluster-encapsulated supramolecular boxes

A dual-templated approach for the controllable synthesis of metal cluster complexes is described. By using an acetylide-containing anion with specific geometry as a central template and a macrocyclic coordinative compound as a peripheral one, two multinuclear silver-acetylide cluster-encapsulated supramolecular boxes were synthesized.

Surface modification of polyoxometalate host–guest supramolecular architectures: from metal–organic pseudorotaxane framework to molecular box

Precise controlling of the pH value leads to the formation of a new type of metal-organic pseudorotaxane framework and supramolecular box within accommodating POMs guests.

Photoinduced Processes in Self-Assembled Porphyrin/Perylene Bisimide Metallosupramolecular Boxes

Two new supramolecular boxes, (ZnMC)(2)(rPBI)(2) and (ZnMC)(2)(gPBI)(2), have been obtained by axial coordination of N,N'-dipyridyl-functionalized perylene bisimide (PBI) dyes to the zinc ion centers of two 2+2 porphyrin metallacycles (ZnMC = [trans,cis,cis-RuCl(2)(CO)(2)(Zn·4'-cis-DPyP)](2)). The two molecular boxes involve PBI pillars with different substituents at the bay area: the "red" PBI (rPBI = N,N'-di(4-pyridyl)-1,6,7,12-tetra(4-tert-butylphenoxy)perylene-3,4:9,10-tetracarboxylic acid bisimide) containing tert-butylphenoxy substituents and the "green" PBI (gPBI = N,N'-di(4-pyridyl)-1,7-bis(pyrrolidin-1-yl)perylene-3,4:9,10-tetracarboxylic acid bisimide) bearing pyrrolidinyl substituents. Due to the rigidity of the modules and the simultaneous formation of four pyridine-zinc bonds, these discrete adducts self-assemble quantitatively and are remarkably stable in dichloromethane solution. The photophysical behavior of the new supramolecular boxes has been studied in dichloromethane by emission spectroscopy and ultrafast absorption techniques. A different photophysical behavior is observed for the two systems. In (ZnMC)(2)(rPBI)(2), efficient electron transfer quenching of both perylene bisimide and zinc porphyrin chromophores is observed, leading to a charge separated state, PBI(-)-Zn(+), in which a perylene bisimide unit is reduced and zinc porphyrin is oxidized. In the deactivation of the perylene bisimide localized excited state, an intermediate zwitterionic charge transfer state of type PBI(-)-PBI(+) seems to play a relevant role. In (ZnMC)(2)(gPBI)(2), singlet energy transfer from the Zn porphyrin chromophores to the perylene bisimide units occurs with an efficiency of 0.7. This lower than unity value is due to a competing electron transfer quenching, leading to the charge separated state PBI(-)-Zn(+). The distinct photophysical behavior of these two supramolecular boxes is interpreted in terms of energy changes occurring upon replacement of the "red" rPBI by "green" gPBI.

The Assembly of Supramolecular Boxes and Coordination Polymers Based on Bis‐Zinc‐Salphen Building Blocks

We report the assembly of supramolecular boxes and coordination polymers based on a rigid bis-zinc(II)-salphen complex and various ditopic nitrogen ligands. The use of the bis-zinc(II)-salphen building block in combination with small ditopic nitrogen ligands gave organic coordination polymers both in solution as well as in the solid state. Molecular modeling shows that supramolecular boxes with small internal cavities can be formed. However, the inability to accommodate solvent molecules (such as toluene) in these cavities explains why coordination polymers are prevailing over well-defined boxes, as it would lead to an energetically unfavorable vacuum. In contrast, for relatively longer ditopic nitrogen ligands, we observed the selective formation of supramolecular box assemblies in all cases studied. The approach can be easily extended to chiral analogues by using chiral ditopic nitrogen ligands.

Cavity-Tailored, Self-Sorting Supramolecular Catalytic Boxes for Selective Oxidation

Using a steric self-sorting strategy, the assembly of highly ordered and rigid supramolecular boxes possessing catalytic properties has been achieved in one step. The formation of these assemblies, comprising up to 18 porphyrin centers, was readily confirmed by solution X-ray scattering in conjunction with fluorescent spectroscopy. Size-selective and enantioselective oxidation catalysis were both demonstrated.

ZnII–Salphen Complexes as Versatile Building Blocks for the Construction of Supramolecular Box Assemblies

Zn(II)-salphen complexes are readily accessible and interesting supramolecular building blocks with a large structural diversity. Higher-order supramolecular assemblies, such as molecular boxes based on a bis-Zn(II)-salphen building block and various ditopic bipyridine ligands, have been constructed by means of supramolecular, coordinative Zn(II)-N(pyr) interactions. The use of bipyridine ligands of differing sizes enables the construction of structures with predefined box diameters. The features of the 2:2 box assemblies were investigated in detail by (variable temperature) NMR spectroscopy, UV-visible spectroscopy, NMR titrations, and X-ray crystallographic studies. The spectroscopic studies reveal a high association constant for the Zn(II)-salphen-pyridyl motif, which lies in the range 10(5)-10(6) M(-1). The strong interaction between the Zn(II) center and pyridine donors was supported by PM3 calculations that showed a relatively high Lewis acid character of the metal center in the salphen complex. Titration curves monitored by UV-visible show a cooperative effect between the two bipyridine ligands upon complexation to the bis-Zn(II) template, suggesting the formation of 2:2 complexes. The crystal structures of two supramolecular boxes have been determined. In both examples such a 2:2 assembly is present in the solid state, and the box size is different because they consist of different building blocks. Interestingly, the box assemblies line up in the solid state to form porous channels that are potentially useful in a number of applications.

Self-assembly of supramolecular boxes

Supramolecular boxes are prepared from a dinucleating ligand and redox-active metal centres incorporated into the cavity framework without the need for ancillary ligands to block coordination sites on the metal; crystal structures of copper(I) and cadmium(II) cage structures of 4-thiomethyl-6-(3-pyridyl)-2,2′-bipyridine are reported.

Controlled aggregation of supramolecular boxes

Supramolecular boxes are prepared and their aggregation controlled by self-assembly; the crystal structure of a polymeric assembly of silver(i) cage units of 4-thiomethyl-6-(4-pyridyl)-2,2′-bipyridine is reported.

Crystal engineering: honeycomb networks, molecular laminates and supramolecular boxes

Crystal engineering: honeycomb networks, molecular laminates and supramolecular boxes