This article describes the developments in coordination self-assembly based on flexible tripodal ligands with different metal species. Various finite metallocages such as M₃L₂, M₆L₈, M₆L₄, M₄L₄ and different catenanes based on discrete metallocages constructed from flexible tripodal ligands with suitable metal species are presented here. Many M₃L₂ metallocages based on ligands L¹–L¹² and different two-coordinated metal species have been prepared, in which various Ag(I) salts and other metal species that have been protected by suitable groups, such as Zn(OAc)₂, ZnBr₂, and PdBr₂, have been used as effective acceptors. All of the M₆L₈-type metallocages are constructed from ligands L² or L¹²–L²⁰ and different four-coordinated metal species, such as various palladium(II) salts or NiCl₂, and have similar topological structures. Only a few discrete M₆L₄-type metallocages, based on ligands L²¹–L²⁴, have been reported, using different strategies such as protecting groups and steric hindrance. All of the M₄L₄-type cages have similar topological structures and are constructed from ligands L²⁵–L²⁹ with multiple donor sites. More intriguing interlocking ensembles constructed from discrete metallocages are also described here in detail, namely, three [2]catenanes based on ligands L³⁰–L³² and four polycatenanes based on ligands L³³–L³⁴.

A novel coordination polymer, formulated as Zn₆(TIB)₄(BPTC)₃(DMA)₄(H₂O)₁₀ [TIB=1,3,5-tris(1-imidazolyl)-benzene, H₄BPTC=3,3′,5,5′-biphenyltetracarboxylate], has been synthesized and structurally characterized. Further investigations reveal that it presents a new topology (topological symbol {6².8⁴}{6³}4{6⁵.8}6{6⁶}2) based on self-penetration, and shows interesting fluorescent properties.

Three new compounds, CuL, CuL′, and Cu₂O₂L′′₂ (H₂L=3′-[(E)-{[(1S,2S)-2-aminocyclohexyl]imino}methyl]-4′-hydroxy-4-biphenylcarboxlic acid, H₂L′=3′-[(E)-{[(1S,2S)-2-aminocyclohexyl]imino}methyl]-4′-hydroxy-5′-nitro-4-biphenylcarboxlic acid, H₂L′′=3′-(N,N-dimethylamino methyl)-4′-hydroxy-4-biphenylcarboxlic acid), were selectively synthesized through a controlled in situ ligand reaction system mediated by copper(II) nitrate and H₂L. Selective nitration was achieved by using different solvent mixtures under relatively mild conditions, and an interesting and economical reductive amination system in DMF/EtOH/H₂O was also found. All crystal structures were determined by single-crystal X-ray diffraction analysis. Both CuL and CuL′ display chiral 1D chain structures, whereas Cu₂O₂L′′₂ possesses a structure with 13×16 Å channels and a free volume of 41.4 %. The possible mechanisms involved in this in situ ligand-controlled reaction system are discussed in detail.

Tripodal host 2,4,6-tris(1-phenyl-1H-tetrazolylsulfanylmethyl)mesitylene (TPTM) has been synthesized through a facile procedure. As expected, it adopts an all-syn cylindrical configuration, thereby delimiting an inner cavity. To explore the solvatomorphism and inclusion behavior of TPTM, a series of organic and inorganic species were employed as guests to afford 17 inclusion compounds (1, 2, 3 a–3 f, 4 a–4 i) that can be classified into four distinct forms (forms I–IV), under similar conditions. These compounds were characterized by single-crystal and powder X-ray diffraction, and ¹H NMR studies. In compound 1 with form I, one foot of a TPTM molecule inserts into the cavity of an opposite TPTM molecule to form a dimeric “hand-shake” motif with one acetonitrile molecule occupying the void. Compound 2 with form II contains three types of capsule-shaped dimers, each of which holds a CH₂Cl₂ molecule as the guest. In compounds 3 a–3 f with form III, each pair of TPTM molecules interdigitates to form a capsule-shaped dimeric unit accommodating a guest molecule in the endo-cavity. In compounds 4 a–4 i with form IV, each TPTM molecule makes contact with three nearby TPTM molecules in a “self-including” manner to generate a graphite-like organic layer, and through further superposition to form open hexagonal channels. From the experimental and theoretical results, the intrinsic properties of guest molecules, such as size, shape, and self-interaction, can be regarded as the main factors leading to these solvatomorphism phenomena and the subtle inclusion behavior of TPTM. Thermogravimetric analyses show that the encapsulated guest molecules in these compounds can be evacuated at relatively high temperatures, and this demonstrates the outstanding inclusion capability of TPTM. In addition, for compound 4 a with benzene molecules in the channels, reversible exchange of toluene and separation of xylene isomers on single crystals have been observed.

As a new member of the water-soluble calixarene family, p-sulfonatothiacalix[4]arene possesses unique properties resulting from its inherent structural characteristics. In our recent research, we have investigated the self-assembly of bowl-like p-sulfonatothiacalix[4]arenes with or without transition-metal ions in the presence of suitable guests. We have obtained a series of compounds with different structural motifs, such as capsules, tetranuclear clusters, and molecular clefts. In addition, p-sulfonatothiacalix[4]arenes show good inclusion abilities and can capture different guests by utilizing their hydrophobic cavities through supramolecular interactions. Even when a cone-like conformation is fixed, the p-sulfonatothiacalix[4]arene can also splay its opposite aromatic rings apart to adjust its cone-like conformations from C_4v to C_2v and even lower symmetries. All of these show that it is a good candidate for the research of inclusion phenomena. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 155–168; 2009: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.200800033