[PMo 12 O 40 ] 3– ‐Induced Perhydroxycucurbit[5]uril‐Based Porous Supramolecular Assemblies

Large anion binding in water

Large water-soluble anions with chaotropic character display surprisingly strong supramolecular interactions in water, for example, with macrocyclic receptors, polymers, biomembranes, and other hydrophobic cavities and interfaces. The high affinity is traced back to a hitherto underestimated driving force, the chaotropic effect, which is orthogonal to the common hydrophobic effect. This review focuses on the binding of large anions with water-soluble macrocyclic hosts, including cyclodextrins, cucurbiturils, bambusurils, biotinurils, and other organic receptors. The high affinity of large anions to molecular receptors has been implemented in several lines of new applications, which are highlighted herein.

Cucurbit[n]uril-Based Supramolecular Frameworks Assembled through Outer-Surface Interactions

Porous materials, especially metal-organic frameworks, covalent organic frameworks, and supramolecular organic frameworks, are widely used in heterogeneous catalysis, adsorption, and ion exchange. Cucurbit[n]urils (Q[n]s) suitable building units for porous materials because they possess cavities with neutral electrostatic potential, portal carbonyls with negative electrostatic potential, and outer surfaces with positive electrostatic potential, which may result in the formation of Q[n]-based supramolecular frameworks (QSFs) assembled through the interaction of guests within Q[n]s, the coordination of Q[n]s with metal ions, and outer-surface interaction of Q[n]s (OSIQ). This review summarizes the various QSFs assembled via OSIQs. The QSFs can be classified as being assembled by 1) self-induced OSIQ, 2) anion-induced OSIQ, and 3) aromatic-induced OSIQ. The design and construction of QSFs with novel structures and specific functional properties may establish a new research direction in Q[n] chemistry.

Supramolecular chemistry of substituted cucurbit[n]urils

This review covers important advances in the field of substituted cucurbit[n]urils.

Lanthanoid Heteroleptic Complexes with Cucurbit[5]uril and Dicarboxylate Ligands: From Discrete Structures to One-Dimensional and Two-Dimensional Polymers

Lanthanoid heteroleptic complexes with cucurbit[5]uril {Q[5]} and two dicarboxylate ligands, e.g., diglycolic acid (H₂DGC) and glutaric acid (H₂GT), have been investigated with six new compounds featuring a tetrametallic and dimetallic discrete structures, a one-dimensional (1D) polymer, and three two-dimensional (2D) polymers with a unique honeycomb-type topology being synthesized and structurally characterized. [La₄(Q[5])₃(DGC)₂(NO₃)₂(H₂O)₁₂][La(DGC)(H₂O)₆]·7NO₃· nH₂O (1) has a tetrametallic structure constructed with three bis-bidentate Q[5] ligands linking two [La(DGC)(H₂O)₂]⁺ species in the middle and two [La(H₂O)₄(NO₃)]²⁺ species at both ends. [Ce₂(Q[5])(DGC)(NO₃)(H₂O)₁₀]·3NO₃·4H₂O (2) has a dimetallic structure built up with a bis-bidentate Q[5] ligand linking [Ce(DGC)(H₂O)₃(NO₃)] and [Ce(H₂O)₇]³⁺ on each side of the Q[5] portals. [Ce₃(Q[5])₃(DGC)₂(H₂O)₉][Ce(DGC)(H₂O)₆]₂·7NO₃· nH₂O (3) has a 1D polymeric structure built up with bis-bidentate Q[5] ligands in-turn linking one [Ce(H₂O)₆]³⁺ and two [Ce(DGC)(H₂O)₆]¹⁺ cationic species. [Ln₂(Q[5])₂(GT)(H₂O)₆]·4NO₃· nH₂O [Ln = La (4), Ce (5) and Nd (6)] have similar 2D polymeric structures built up with two types of 9-fold coordinated Ln polyhedra linked by Q[5] via bis-bidentate carbonyl groups on both sides forming 1D chains which are further connected by bridging GT^2- ligands to form 2D polymers with a unique honeycomb-type topology. Their vibrational modes and electronic structures have also been investigated.

Porous supramolecular assemblies and functional properties of perhydroxylated cucurbit[6]uril and polyoxometallates

(HO)₁₂Q[6] and POMs were used as basic building blocks, and interactions yielded two novel types of supramolecular assemblies at different HCl concentrations.

The Chaotropic Effect as an Assembly Motif in Chemistry

Following up on scattered reports on interactions of conventional chaotropic ions (for example, I- , SCN- , ClO4- ) with macrocyclic host molecules, biomolecules, and hydrophobic neutral surfaces in aqueous solution, the chaotropic effect has recently emerged as a generic driving force for supramolecular assembly, orthogonal to the hydrophobic effect. The chaotropic effect becomes most effective for very large ions that extend beyond the classical Hofmeister scale and that can be referred to as superchaotropic ions (for example, borate clusters and polyoxometalates). In this Minireview, we present a continuous scale of water-solute interactions that includes the solvation of kosmotropic, chaotropic, and hydrophobic solutes, as well as the creation of void space (cavitation). Recent examples for the association of chaotropic anions to hydrophobic synthetic and biological binding sites, lipid bilayers, and surfaces are discussed.

Thorium(IV) and Uranium(IV) Complexes with Cucurbit[5]uril

Tetravalent thorium and uranium complexes with cucurbit[5]uril (Q[5]) were investigated with eight new complexes being synthesized and structurally characterized. [Th(Q[5])(OH)(H₂O)₂]₆·18NO₃· nH₂O (1) has a hexagonal nanowheel structure with each of the six Th⁴⁺ ions being cap-coordinated by a Q[5] and monodentate-coordinated to the nearby Q[5]. [Th(Q[5])(HCOO)(H₂O)₄][Th(NO₃)₅(H₂O)₂]₂[Th(NO₃)₃(HCOO)(H₂O)₂]_0.5·NO₃· nH₂O (2) has a heteroleptic mononuclear structure with a Th⁴⁺ ion cap-coordinated on one side of the Q[5] portal and monodentate-coordinated to a formate anion inside the Q[5] cavity. [KTh_1.5(Q[5])Cl(NO₃)₃][Th(NO₃)₅(H₂O)₂]·2NO₃·2.5H₂O (3) has a heterometallic structure with both Th⁴⁺ and K⁺ ions each occupying one side of the two Q[5] portals forming a capsule. [CsTh(Q[5])Cl(NO₃)₂(H₂O)₃]·2NO₃· nH₂O (4) has a heterometallic 1D polymeric structure with both Th⁴⁺ and Cs⁺ ions each occupying one side of the two Q[5] portals, forming monomers which are linked together by sharing two water molecules and one carbonyl oxygen atom between Th⁴⁺ and Cs⁺ ions. [Th(Q[5])Cl(H₂O)][CdCl₃][CdCl₄]·0.5HCl·4H₂O (5), [Th(Q[5])Cl(H₂O)][Ru₂OCl₉(H₂O)]·0.5HCl·9.5H₂O (6), [Th(Q[5])Cl(H₂O)][IrCl₆]_1.5·3H₂O (7), and [U(Q[5])Cl(H₂O)][ZnCl₃(H₂O)][(ZnCl₄)]·8H₂O (8) have similar 1D polymeric structures with Th⁴⁺/U⁴⁺ ions cap-coordinated on one side of a Q[5] and bidentate coordinated to the nearby Q[5]. The transition metal chlorides act as anions for charge compensation as well as structure inducers via cation-anion interactions forming various anion patterns around the 1D polymers. Actinide contraction has been observed in the early actinide series.

Cucurbit[6]uril-based multifunctional supramolecular assemblies: synthesis, removal of Ba(ii) and fluorescence sensing of Fe(iii)

Supramolecular assemblies formed of cucurbit[6]uril and flexible aromatic compounds were achieved via outer-surface interactions, and show selective adsorption and sensing properties.

Highly selective absorption of polychloromethanes in perhydroxylated cucurbit[6]uril-based supramolecular assemblies

Two perhydroxylated cucurbit[6]uril-based porous assemblies have been obtained by the crystallization of perhydroxylated cucurbit[6]uril {(HO)₁₂Q[6]} from aqueous HCl solutions of different concentrations, which exhibit highly selective absorption of polychloromethanes.

Coordination and supramolecular assembly of {Cd2Ge8V12O48} building block and cucurbit[6] to form rotaxane-shaped hybrids

Assembly of cucurbit[6] and a {Cd2Ge8V12O48} cluster produced two rotaxane-shaped and polyrotaxane-shaped solids by changing the ratio of starting precursors in the system. The high oxygen density of the polyoxoanion surface provides active sites to extend a single rotaxane-shaped hybrid 1 to a 1D polyrotaxane-shaped hybrid 2. This construction strategy may afford an entirely new methodology for polyoxometalate-based hybrid chemistry.

Self-assemblies based on the "outer-surface interactions" of cucurbit[n]urils: new opportunities for supramolecular architectures and materials

Supramolecular architectures and materials have attracted immense attention during the last decades because they not only open the possibility of obtaining a large variety of aesthetically interesting structures but also have applications in gas storage, sensors, separation, catalysis, and so on. On the other hand, cucurbit[n]urils (Q[n]s), a relatively new class of macrocyclic hosts with a rigid hydrophobic cavity and two identical carbonyl fringed portals, have attracted much attention in supramolecular chemistry. Because of the strong charge-dipole and hydrogen bonding interactions, as well as hydrophobic and hydrophilic effect derived from the negative portals and rigid cavities of Q[n]s, nearly all research in Q[n]s has been focused on utilizing the portals and cavities to construct supramolecular assemblies similar to other macrocyclic receptors such as cyclodextrin and calixarenes. Interestingly, a recent study revealed that other weak noncovalent interactions such as hydrogen bonding and π···π stacking, as well as C-H···π and ion-dipole interactions, could also be defined as "outer-surface interactions", which are derived from the electrostatically positive outer surface of Q[n]s. These interactions could be the driving forces in the formation of various novel Q[n]-based supramolecular architectures and functional materials. In this Account, we provide a comprehensive overview of supramolecular self-assemblies based on the outer-surface interactions of Q[n]s. These outer-surface interactions include those between Q[n]s, Q[n]s and aromatic molecules, Q[n]s and calixarenes, Q[n]s and inorganic complex ions, and Q[n]s and polyoxometalates. Pioneering work has shown that such weak noncovalent interactions play very important roles in the formation of various Q[n]-based functional materials and supramolecular architectures. For example, hydrogen bonds in outer-surface interactions between Q[n] molecules not only function as the sole driving force in the formation of one-dimensional Q[n] porous channels but also assist the bonding forces of the channels in capturing and accommodating acetylene molecules and carbon dioxide in the channel cavities. Moreover, upon introduction of a third species such as an aromatic molecule or inorganic anion into the Q[n]/metal system, "outer-surface interactions" could lead to Q[n]/metal-based self-assemblies from simple finite supramolecular coordination complexes to infinite polydimensional supramolecular architectures and other structures. Overall, this Account focuses on the novel self-assembly driving force derived from Q[n]s including (i) concepts of the outer-surface interactions of Q[n]s, (ii) providing plausible explanations of the mechanisms of the outer-surface interactions of Q[n]s, and (iii) introduction of an overview of the developments and practical applications of outer-surface interactions of Q[n]s in supramolecular chemistry. It is hoped that this study based on the outer-surface interactions of Q[n]s can enrich the field of molecular engineering of functional supramolecular systems and provide new opportunities for the construction of functional materials and architectures.