Constructing Supramolecular Frameworks Based Imidazolate-Edge-Bridged Metallacalix[3]arenes via Hierarchical Self-Assemblies

Hierarchical self-assembly of novel supramolecular structures has obtained increasing attention. Herein we design and synthesize the palladium(II)-based molecular basket-like structures, as structural analog of metallacalix[3]arene [M3L3]3+ (M = (dmbpy)Pd, (phen)Pd; dmbpy = 4,4’-dimethyl-bipyridine; phen = 1,10-phenanthroline), by coordination-driven self-assembly from imidazolate-containing ligand [4,5-bis(2,5-dimethylthiophen-3-yl)-1H-imidazole (HL) with palladium(II) nitrate precursors (dmbpy)Pd(NO3)2 and (phen)Pd(NO3)2. The difference of the palladium(II) nitrate precursors with π-surface in complex produces variations of the two-dimensional (2-D) and three-dimensional (3-D) high-ordered supramolecular architectures, constructed by π···π packing and hydrogen bonding interactions, with metallacalixarenes as building blocks. These results provide perceptions of further exploring the hierarchical assembly of supramolecular structures based on π···π packing and multiple hydrogen bonding.

Controlled Self-Assembly and Multistimuli-Responsive Interconversions of Three Conjoined Twin-Cages

Stimuli-responsive structural transformations between discrete coordination supramolecular architectures not only are essential to construct smart functional materials but also provide a versatile molecular-level platform to mimic the biological transformation process. We report here the controlled self-assembly of three topologically unprecedented conjoined twin-cages, i.e., one stapled interlocked Pd₁₂L₆ cage (2) and two helically isomeric Pd₆L₃ cages (3 and 4) made from the same cis-blocked palladium corners and a new bis-bidentate ligand (1). While cage 2 features three mechanically coupled cavities, cages 3 and 4 are topologically isomeric helicate-based twin-cages based on the same metal/ligand stoichiometry. Sole formation of cage 2 or a dynamic mixture of cages 3 and 4 can be controlled by changing the solvents employed during the self-assembly. Structural conversions between cages 3 and 4 can be triggered by changes in both temperature/solvent and induced-fit guest encapsulations. Well-controlled interconversion between such topologically complex superstructures may lay a solid foundation for achieving a variety of functions within a switchable system.

Polyoxometalate-Incorporated Metallacalixarene@Graphene Composite Electrodes for High-Performance Supercapacitors

Composites of polyoxometalate (POM)/metallacalixarene/graphene-based electrode materials not only integrate the superiority of the individual components perfectly but also ameliorate the demerits to some extent, providing a promising route to approach high-performance supercapacitors. Herein, first, we report the preparations, structures, and electrochemical performance of two fascinating POM-incorporated metallacalixarene compounds [Ag₅(C₂H₂N₃)₆][H₅ ⊂ SiMo₁₂O₄₀] (1) and [Ag₅(C₂H₂N₃)₆][H₅ ⊂ SiW₁₂O₄₀] (2); (C₂H₂N₃ = 1 H-1,2,4-triazole). Single-crystal X-ray diffraction analyses illustrated that both 1 and 2 possess intriguing POM-sandwiched metallacalix[6]arene frameworks. Nevertheless, our investigations, including the electrochemical cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy, reveal that the oxidation ability of the Keggin ions is a primary effect in electrochemical performance of these POM-incorporated metallacalixarene compounds. Namely, the electrodes containing Mo as metal atoms in the Keggin POM shows much higher capacitance than the corresponding W-containing ones. Moreover, compound 1@graphene oxide (GO) composite electrodes are fabricated and systematically explored for their supercapacitor performance. Thanks to the synergetic effects of GO and POM-incorporated metallacalixarenes, the compound 1@15%GO-based electrode exhibits the highest specific capacitance of up to 230.2 F g^-1 (current density equal to 0.5 A g^-1), which is superior to majority of the reported POM-based electrode materials.

Self-Assembly of Aluminum- and Gallium-Based meso-Metallaporphyrins

The molecular meso-metallaporphyrin has been obtained from the reaction of AlMe₃ with the bulky 4,5-(Ph₂(HO)C)₂-1,2,3-triazole (1). The presence of Al-Me groups coordinated to the triazole rings creates three different stereoisomers that were identified by single-crystal X-ray diffraction. Further studies revealed that, for steric reasons, only one of the two main stereoisomers is active in the polymerization of ε-caprolactone. When GaMe₃ is used instead of AlMe₃, a trimetallic species is formed instead of the meso-metallaporphyrin pointing to a metal-directed self-assembly. On the other hand, the reaction of the monolithium salt [{Li(THF)₂}{κ²- N, N'-4,5-(Ph₂(HO)C)-1,2,3-triazole}]₂ (2; THF = tetrahydrofuran) with MCl₃ (M = Al, Ga) yields meso-metallaporphyrin species with a lithium atom in the center of the metallacycle. While the gallium derivative is rather stable in solution, the aluminum analogue decomposes rapidly. In the solid state, continuous cationic columns running throughout the whole crystal are formed from alternating Li⊂[M]₄ (M = Al, Ga) meso-metallaporphyrin and [Li(THF)₄]⁺ cations. Density functional theory calculations determined that the weak Cl···H, H···H, N···H, and Cl···O interactions with a total interaction energy of -38.6 kcal·mol^-1 are responsible for this unusual packing.