Li-Li Liang

Construction of Cucurbit[7]uril Based Tubular Nanochannels Incorporating Associated [CdCl4]2- and Lanthanide Ions

There is intensive interest in the design of tubular channels because of their novel structures and various applications in a variety of research fields. Herein, we present a series of coordination-driven Q[7]-derived organic nanochannels using an anion-induced strategy under different acid concentrations. An advantage of this approach is that the tubular channels not only retain the original character of the parent macrocyclic receptors but also provide deep hydrophobic cavities possessing guest binding sites. Importantly, this study also emphasizes the efficiency of the macrocyclic receptors in providing a tubular hydrophobic cavity by directly stacking on top of one another with the anion-fixed and by acid control. The resulting combination of hydrogen bonding, C-H···Cl, and ion-dipole interactions helps to stabilize these supramolecular architectures. Such systems are both tunable and versatile and allow for interconvertibility in the construction of nanochannels based on these macrocyclic receptors.

Inorganic anion-aided coordination of lanthanide metal ions to cucurbituril and supramolecular self-assembly: potential applications in the separation of light lanthanides

Linear coordination polymers have been assembled from lanthanide cations (Ln3+) and cucurbituril (Q[6]) in the presence of [CdCl4]2− or [ZnCl4]2− anions as inorganic structure inducers in HCl solution. X-ray diffraction analysis has revealed honeycomb-patterned supramolecular assemblies, in which [CdCl4]2− or [ZnCl4]2− anions form the honeycomb and the hexagonal cells are occupied by Ln3+–Q[6] linear coordination polymers. For the Ln3+–Q[6]–[CdCl4]2− systems, the solid-state structures of the obtained compounds were all isomorphous, with the Ln3+ cations coordinated to Q[6] to form zigzag coordination polymers that fill the [CdCl4]2− honeycombs. For the Ln3+–Q[6]–[ZnCl4]2− systems, the obtained compounds were divided into two groups of four and five isomorphous complexes, respectively. Besides the zigzag coordination polymers, tubular coordination polymers occupying the [ZnCl4]2− honeycombs were also observed. The most remarkable phenomenon in the present work was the rapid precipitation of the Ln3+–Q[6]–[CdCl4]2− or –[ZnCl4]2− systems when the Ln3+ cations were La, Ce, Pr or Nd. This may offer a means of separating light lanthanides cations from their heavier counterparts.

Coordination nanotubes self-assembled from cucurbit[7]uril and lanthanide cations

A series of complexes based on the macrocyclic ligand cucurbit[7]uril (Q[7]) with formulas {La2(H2O)12Q[7]}·2(ZnCl4)·2Cl·31H2O (1), {Ln2(H2O)12Q[7]}·2(ZnCl4)·2Cl·xH2O [isomorphous with Ln = Ce (2), Pr (3) and Nd (4), x = 25 (2), 29 (3) and 25 (4)], and {Ln2(H2O)10Q[7]}·2(ZnCl4)·2Cl·xH2O [isomorphous with Ln = Sm (5), Gd (6), Tb (7), Er (8), Tm (9), Yb (10) and Lu (11), x = 24 (5), 27 (6), 27 (7), 33 (8), 27 (9), 18 (10) and 29 (11)], have been synthesized by the self-assembly of Q[7] with the corresponding lanthanide species in the presence of ZnCl2. The single-crystal X-ray diffraction analyses reveal that the eleven complexes are separated into three types of coordination nanotubes given different coordination environments of the lanthanide(III) ions. The eleven complexes display interesting structural progressions, which are mainly ascribed to the effect of lanthanide contraction. Their thermal and IR properties were also examined.

[CdCl4]2− anion-induced coordination of Ln3+ to cucurbit[8]uril and the formation of supramolecular self-assemblies: potential application in isolation of light lanthanides

The coordination and supramolecular assemblies of Q[8] with lanthanides in the presence of [CdCl4]2− anions show significant differences, which could be used for the isolation of light lanthanides from their heavier counterparts.

Hydroquinone-assisted assembly of coordination polymers from lanthanides and cucurbit[5]uril

Coordination polymers have been assembled from a series of eight different lanthanide ions (Ln3+) and cucurbit[5]uril (Q[5]) in the presence of hydroquinone (Hyq) as an organic structure inducer. X-ray diffraction analysis has revealed three distinct configurations of the coordination polymers formed with increasing atomic number of the lanthanide. The coordination of light lanthanide cations to Q[5] leads to the formation of linear one-dimensional coordination polymers; the coordination of intermediate lanthanide cations such as Eu(III) or Gd(III) leads to the formation of Q[5] pairs in which the two Q[5] molecules are connected by the Eu(III) or Gd(III) ions; and the coordination of heavy lanthanide cations to Q[5] leads to the formation of homochiral one-dimensional helical coordination polymers.

Tetrachloride transition-metal dianion-induced coordination and supramolecular self-assembly of strontium dications to cucurbit[8]uril

In the present work, we describe a kind of novel cucurbit[8]uril-based coordination supramolecular self-assembly taking place in the presence of tetrachloride transition-metal dianions ([MtransCl4]2−, Mtrans = Cd, Zn, Cu, Co) in HCl solution. As reported previously, the “honeycomb effect” of the tetrachloride transition-metal dianion ([MtransCl4]2− has been observed in the coordination of strontium cations to cucurbit[8]uril molecules (Q[8]s). It seems that the [MtransCl4]2− anions form a honeycomb structure with hexagonal cells filled with Sr2+–Q[8] linear coordination polymers in which the Sr2+ cations coordinate to Q[8] molecules and form zigzag coordination polymers.

p-Hydroxybenzoic acid-induced formation of a novel framework based on direct coordination of caesium ions to cucurbit[8]uril

A novel three dimensional framework, generated by crystallisation of the ternary mixture of Q[8], CsCl and p-hydroxybenzoic acid (Hyb) has the formula {Cs(H2O)[(Hyb)2@Q[8]]2}+2Hyb·Cl−·24H2O. The crystal structure shows that the 3D framework is constructed from the four Q[8] molecule units through the Hyb-induced coordination of the caesium pair to the portal oxygens of the Q[8]s.

Tetrachloridometallate Dianion-Induced Cucurbit[8]uril Supramolecular Assemblies with Large Channels and Their Potential Applications for Extraction Coating on Solid-Phase Microextraction Fibers

Q[8]-based porous materials were synthesized in the presence of [Md-blockCl4](2-) anions as structure inducers. The driving forces of the structure-directing effect of the [Md-blockCl4](2-) anions may be due to the ion-dipole interaction and hydrogen bonding between the [Md-blockCl4](2-) anions and ≡CH or ═CH2 groups on the backs of Q[8] molecules. Moreover, the tests of potential applications show that these porous materials can not only capture organic molecules through the cavity of Q[8] moieties but also adsorb larger organic molecules with different selectivities.

p-Hydroxybenzoic acid-assisted homochiral 1D-helical coordination polymers from calcium cations and cucurbit[5]uril

A homochiral 1D-helical coordination polymer has been assembled from calcium ions (Ca2+) and cucurbit[5]uril (Q[5]) in the presence of p-hydroxybenzoic acid (Hyb) as an organic structure inducer. This result shows that a homochiral 1D-helical coordination polymer can be obtained from Q[5] with not only heavy lanthanides but also other metal ions, such as calcium dications in the present case, and that p-hydroxybenzoic acid (Hyb) can serve as an organic structure inducer in place of the previously used hydroquinone (Hyq). Control experiments by X-ray diffraction analysis have shown that Q[5] coordinates with the calcium cations to form a linear coordination polymer in the absence of Hyb, while a mixture of Q[5] and Hyb, without a metal salt under the same synthetic conditions, produces Q[5]-based linear supramolecular chains linked by hydrogen-bonding networks, which lie in a Hyb-based net.

The synthesis of networks based on the coordination of cucurbit[8]urils and alkali or alkaline earth ions in the presence of the polychloride transition-metal anions

To extend the strategy for the induced formation of cucurbit[n]uril–metal by a third species, we introduced alkali or alkaline earth metal ions (Malkali or alkaline earth metal) into cucurbit[8]uril (Q[8])–HCl systems in the presence of polychloride transition-metal anions. The polychloride transition-metal anions acted as structure inducers. A series of Q[8]–Malkali or alkaline earth metal complexes and their corresponding two-dimensional (2D) supramolecular assemblies were first synthesized and characterized by single-crystal X-ray diffraction analysis. The crystal structural analysis revealed that the Q[8]-based trigonal-planar branches in the related compounds are the key building blocks for the construction of the novel 2D Q[8]–Malkali or alkaline earth metal networks in which one or two alkali or alkaline earth metal ions link three Q[8] molecules through direct coordination. Moreover, the novel 2D Q[8]–Malkali or alkaline earth metal networks have a honeycomb shape with hexagonal “nanoholes”. The superimposition of the 2D networks could create novel nanochannels which numerous water molecules and counter anions could occupy.