Rui-Lian Lin

Anion channel structure through packing of cucurbit[5]uril-Pb2+ or cucurbit[5]uril-Hg2+ complexes

In this study, complexes {[Pb4(C30H30N20O10)2Cl2]Cl2(H2O)2}PbCl6 · 12H2O (1) and [Hg(C30H30N20O10)Cl2] · 6H2O (2) have been synthesized and structurally characterized. Single-crystal X-ray diffraction analyses reveal that water-soluble toxic metal ions, Pb2+ and Hg2+, can be chelated by cucurbit[5]uril to form molecular capsule and molecular bowl. Moreover, solid-state packing of these molecular capsule or molecular bowl shows the formation of a channel, in which octahedral [PbCl6]4− or tetrahedral [HgCl4]2− anions were encapsulated.

Anion encapsulation by Ln(III)/K(I) heterobismetal-capped cucurbit[5]uril

Three Ln(III)/K(I) (Ln = La, Ce and Nd) heterobismetal-capped cucurbit[5]uril molecular capsules, {[LaK(C30H30N20O10)Cl]Cl(H2O)3}Cl2·8H2O (1), {[CeK(C30H30N20O10)Cl]Cl(H2O)3}Cl4(H3O)2 2 + ·8H2O (2) and {[NdK(C30H30N20O10)Cl]Cl(H2O)3}Cl2·12.5H2O (3), were synthesised by self-assembly in aqueous solution, and their anion encapsulation property was confirmed by X-ray crystallography. The effect of the lanthanide cation radius on the structure of the heterobismetal-capped cucurbit[5]uril molecular capsules has been investigated.

Coordination complexes based on pentacyclohexanocucurbit[5]uril and lanthanide(III) ions: lanthanide contraction effect induced structural variation

Eight coordination complexes, {LnCl2(H2O)3Q*[5]}·NO3·18.5H2O [isomorphous for Ln = La (1), Ce (2) and Pr (3)], {LnCl2(H2O)2Q*[5]}·NO3·14H2O [isomorphous for Ln = Nd (4) and Sm (5)], {Dy(H2O)2[Cl ⊂ Q*[5]]Dy(H2O)6}·5Cl·20H2O (6), {LnCl(H2O)[Cl ⊂ Q*[5]]Ln(H2O)6}·4Cl·13H2O [isomorphous for Ln = Ho (7) and Er (8)], were obtained by reactions of the corresponding lanthanide species with the macrocyclic ligand pentacyclohexanocucurbit[5]uril (Q*[5]) in aqueous solution, and their structures were determined by single-crystal X-ray diffraction. Crystal structure analysis reveals that, in complexes 1–5, each Q*[5] coordinates to one lanthanide(III) ion to form an opened molecular capsule structure, and then adjacent molecular capsules bridge each other to form a 1-D coordination polymer structure, while in complexes 6–8, each Q*[5] coordinates to two lanthanide(III) ions to form a 0-D half-opened molecular capsule structure. These complexes show that their structural variations are ascribed to the effect of lanthanide contraction.

Self-assembly of cucurbit[8]uril-based polypseudorotaxanes using host–guest interactions

Two inclusion complexes formed on self-assembly of the Q[8] host with dihexyl-4,4′-bipyridinium (HV2+) dibromide and 1,3-bis(4-butylpiperazin-1-yl)-propane (C3PA2+) dibromide guests have been characterized by X-ray crystallography, which clearly shows how the hosts and the guests interlock with each other using supramolecular interactions, eventually generating novel polypseudorotaxanes.

Ionic radius-dependent self-assembly of closed/opened molecular capsules based on pentacyclopentanocucurbit[5]uril

Three coordination architectures, namely, {Ca2(H2O)4[(NO3)⊂Q*[5]]}2(NO3)6·26H2O (1), {Sr2(H2O)3(NO3)[(NO3)⊂Q*[5]]}(NO3)2·7H2O (2), {Ba(H2O)[(H2O)2 ⊂ Q*[5]]}–(NO3)2·11H2O (3), have been synthesized by reactions of the corresponding alkaline-earth metal salts with pentacyclopentanocucurbit[5]uril (Q*[5]). These compounds were characterized by single-crystal X-ray diffraction studies, showing that the ionic radius of the alkaline-earth metal plays a crucial role in determining which type of molecular capsule forms. Compound 1 is an incompletely closed molecular capsule, compound 2 corresponds to a closed molecular capsule, and compound 3 resembles an opened molecular capsule. The thermogravimetric analysis (TGA) of compound 2 was also characterized.

Inclusion of methylviologen in symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril

The host–guest interaction between symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril (TMeQ[6]) and methylviologen (N,N′-dimethyl-4,4′-bipyridinium, MV) dication was investigated both in aqueous solution and in the solid state using NMR spectroscopic methods and single-crystal X-ray diffraction analysis. In the aqueous solution, TMeQ[6] forms a 1 : 1 inclusion complex with methylviologen MV2+, and the chemical exchange of the MV2+ guest in and out of the cavity of the TMeQ[6] host was fast on the NMR time scale. In the solid state, however, the MV2+ guest was partially encapsulated into the TMeQ[6] host. We found that the chemical environment of the TMeQ[6] host underwent a severe change during the encapsulation process. Interestingly, electrochemical studies revealed that, unlike other cucurbiturils, TMeQ[6] has the same level of binding affinity to the charged forms (MV2+ and MV+˙) and the fully reduced form (MV0). These studies contribute to the fundamental understanding of the interdependence of electron-transfer processes and molecular recognition.

Supramolecular complexes of α,α′,δ,δ′-tetramethyl-cucurbit[6]uril binding with enantiomeric amino acids

The reaction of α,α′,δ,δ′-tetramethyl-cucurbit[6]uril (TMeQ[6]) with seven enantiopure amino acids (D,L-Gln; D,L-Met; D,L-Ser; D-Val) yields seven supramolecular assemblies under different conditions. Single-crystal X-ray diffraction analyses reveal that the seven supramolecular assemblies are classified into two structural types (inclusion and exclusion structures), which mainly depend on the length of the alkyl chain of the amino acids. In contrast, the reaction of TMeQ[6] with L-Val does not form any crystalline materials, suggesting that TMeQ[6] may be suitable for the separation of D-Val from its enantiomer.

Anion concentration control in the self-assembly of symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril-based tubular architectures

Three supramolecular architectures, namely, (C40H44O12)·(H3O)44+·(CuCl4)24−·8H2O (1), [(C40H44O12)(CuCl2)2(H2O)4]·10H2O (2), (C40H44O12)·14H2O (3), have been successfully synthesized through the reaction of symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril (TMeQ[6]) with CuCl2 at different chloride anion concentration conditions. In the structure of compound 1, which is formed in 6.0 M hydrochloric acid solution, tetrahedral [CuCl4]2− dianions and TMeQ[6] macrocycles are linked into a 1D tubular structure through hydrogen bonding, C–H⋯Cl contacts, and ion–dipole interactions. The compound 2 is isolated in 3.0 M hydrochloric acid solution, in which Cu2+ ions were found to be directly coordinated to the carbonyl oxygens of TMeQ[6] macrocycles and generated a tubular coordination polymer. A further decrease of chloride anion concentration to 1.0 M leads to compound 3, in which no Cu2+ was located and TMeQ[6] macrocycles are packed into a 3D supramolecular assembly containing numerous 1D tubular channels.

Host–guest complexation of HMeQ[7] with alkyldiammonium ions and alkyldiamines: a comparative study

This work presents the host–guest complexation of HMeQ[7] with a series of alkyldiammonium ions and the corresponding uncharged alkyldiamines (H2N(CH2)nNH2, n = 2, 4, 6, 8, 10, 12) in aqueous solution. 1H NMR data indicate that all alkyldiamines and alkyldiammonium ions have inclusion interactions with HMeQ[7] except for the ethanediamine. The driving force for the formation of HMeQ[7]–alkyldiammonium inclusion complexes appears to be the ion–dipole interaction, while the complexation of HMeQ[7] with alkyldiamines mostly depends on the hydrophobic effect. ITC study points out that the host–guest complexation of HMeQ[7] with alkyldiammonium ions is driven by enthalpy and entropy, while the host–guest complexation of HMeQ[7] with alkyldiamines is driven exclusively by enthalpy. The features of weak basicity and absence of charged groups of the alkyldiamines are responsible for the large negative entropy and large enthalpy change in the complexation process of HMeQ[7] with alkyldiamines.

Acetate anion-selective encapsulation in the ellipsoidal cavity of symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril

Four symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril-based compounds have been prepared and characterised by X-ray crystallography. Their crystal structures displayed the acetate anion-selective encapsulating capability of symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril. The host–guest interaction between the symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril and the acetate anion in aqueous solution has also been observed by variable temperature 1H NMR spectroscopy.