Wen-Qi Sun

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.

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.

1,3-Propanediammonium and 1,12-dodecanediammonium encapsulated in the cavity of symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril

The formation of host–guest inclusion complexes between symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril (TMeQ[6]) and two alkyldiammonium guests (1,3-propanediammonium and 1,12-dodecanediammonium) in aqueous solution and in solid state has been confirmed by 1H NMR spectroscopy, X-ray crystallography and isothermal titration calorimetry (ITC). Their single-crystal X-ray diffraction analyses display that both guests take an extended conformation when bound within the TMeQ[6] cavity. ITC data reveal that the complexation of the alkyldiammonium guests with TMeQ[6] should take into account not only the ion–dipole interactions but also hydrophobic interactions. Moreover, we found that the stability constants for the complex formation of the +NH3(CH2)n with TMeQ[6] are much larger than with Q[6] because of the electron-denoting effects of the methyl groups.

Aniline-containing guests recognized by α,α',δ,δ'-tetramethyl-cucurbit[6]uril host.

The host−guest complexation of symmetrical α,α’,δ,δ’-tetramethyl-cucurbit[6]uril (TMeQ[6]) and cucurbit[7]uril (Q[7]) with a series of aniline-containing guests has been investigated by various experimental techniques including NMR, ITC, and X-ray crystallography. Experimental results indicate that both TMeQ[6] and Q[7] hosts can encapsulate aniline-containing guests to form stable inclusion complexes. However, the oval cavity of TMeQ[6] is more complementary in size and shape to the aromatic ring of the guests than the spherical cavity of Q[7]. Shielding and deshielding effects of the aromatic ring on guests lead to the remarkable chemical shifts of the TMeQ[6] host protons. The rotational restriction of the guests in the oval cavity of TMeQ[6] results in the large negative values of entropy. The X-ray crystal structure of the 1:1 inclusion complex between TMeQ[6] and N,N′-diethyl-benzene-1,4-diamine unambiguously reveals that the aromatic ring of the guest resides in the oval cavity of TMeQ[6].

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.

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.

Encapsulation of 2,2′-(decane-1,10-diyl)-diisoquinoline into cucurbit[6]uril and α,α′,δ,δ′-tetramethyl-cucurbit[6]uril: formation of pseudorotaxanes and polypseudorotaxanes†

Abstract Host–guest complexation of cucurbit[6]uril and α,α′,δ,δ′-tetramethyl-cucurbit[6]uril with 2,2′-(decane-1,10-diyl)-diisoquinolinium has been investigated by 1H NMR, UV and fluorescence spectroscopy in aqueous solution and by X-ray crystallography in solid state. Experimental data suggest that in the aqueous solution, both host molecules form [2]pseudorotaxanes with the host located over the decyl chain of the guest. In the solid state, neighbouring [2]pseudorotaxanes are linked by π⋯π and C–H⋯π interactions, eventually generating polypseudorotaxanes.

Binding behaviors of para-dicyclohexanocucurbit[6]uril and meta-tricyclohexanocucurbit[6]uril with dialkyl viologens

Abstract The binding behaviours of para-dicyclohexanocucurbit[6]uril (Cy2Q[6]) and meta-tricyclohexanocucurbit[6]uril (Cy3Q[6]) with a series of dialkyl viologens (MV2+, EV2+, PV2+, BV2+, FV2+ and HV2+) have been investigated by various methods. In the aqueous solution, 1H NMR spectra suggest that the alkyl chains are more favourably encapsulated into the hydrophobic cavities of both hosts than the aromatic rings. Cyclic voltammograms (CV) curves show that the Cy2Q[6] or Cy3Q[6] bind the charged viologens more strongly than the reduced viologens. Isothermal titration calorimetry (ITC) data reveal that the binding processes of both hosts with viologens are enthalpic driven. In the solid state, the PV2+, BV2+ guests and two Cy3Q[6] hosts generated dumbbell-shaped structures, with two Cy3Q[6] hosts residing over two terminal alkyl chains of the guests. Binding behaviors of para-dicyclohexanocucurbit[6]uril and meta-tricyclohexanocucurbit[6]uril with six dialkyl viologens were investigated by various tools, indicating that the driving forces of the formation of the host−guest inclusion complexes result from the cooperativity of the hydrophobic effect, ion−dipole interaction and van der Waals interaction.