Mingzhao Chen

Giant, Hollow 2D Metalloarchitecture: Stepwise Self-Assembly of a Hexagonal Supramolecular Nut

A polyterpyridinyl building block-based nutlike hexagonal bismetallo architecture with a central hollow Star of David was assembled by a stepwise strategy. This nanoarchitecture can be viewed as a recursive mathematical form that possesses a supramolecular corner-connected cyclic structure, i.e., a triangle or rhombus at various levels of scale or detail. The key metallo-organic ligand (MOL) with four uncomplexed free terpyridines was obtained by a final Suzuki cross-coupling reaction with a tetrabromoterpyridine Ru dimer. The molecular metallorhombus was prepared by reacting the MOL with a 60° bis-terpyridine and Fe(2+). The giant hollow hexagonal nut with a diameter of more than 11 nm and a molecular weight of ca. 33 kDa was obtained in near-quantitative yield by mixing the two types of multi-terpyridine ligands with Fe(2+). The supramolecular architecture was characterized by NMR ((1)H and (13)C), 2D NMR (COSY and ROESY), and DOSY spectroscopies, high-resolution electrospray ionization mass spectrometry, traveling-wave ion mobility mass spectrometry, and transmission electron microscopy.

Self-assembly of a supramolecular hexagram and a supramolecular pentagram

Five- and six-pointed star structures occur frequently in nature as flowers, snow-flakes, leaves and so on. These star-shaped patterns are also frequently used in both functional and artistic man-made architectures. Here following a stepwise synthesis and self-assembly approach, pentagonal and hexagonal metallosupramolecules possessing star-shaped motifs were prepared based on the careful design of metallo-organic ligands (MOLs). In the MOL design and preparation, robust ruthenium–terpyridyl complexes were employed to construct brominated metallo-organic intermediates, followed by a Suzuki coupling reaction to achieve the required ensemble. Ligand LA (VRu2+X, V=bisterpyridine, X=tetraterpyridine, Ru=Ruthenium) was initially used for the self-assembly of an anticipated hexagram upon reaction with Cd2+ or Fe2+; however, unexpected pentagonal structures were formed, that is, [Cd5LA5]30+ and [Fe5LA5]30+. In our redesign, LB [V(Ru2+X)2] was synthesized and treated with 60° V-shaped bisterpyridine (V) and Cd2+ to create hexagonal hexagram [Cd12V3LB3]36+ along with traces of the triangle [Cd3V3]6+. Finally, a pure supramolecular hexagram [Fe12V3LB3]36+ was successfully isolated in a high yield using Fe2+ with a higher assembly temperature.

Constructing High‐Generation Sierpiński Triangles by Molecular Puzzling

Three generations of metalated trigonal supramolecular architectures, so-called metallo-triangles, were assembled from terpyridine (tpy) complexes. The first generation (G1) metallo-triangles were directly obtained by reacting a bis(terpyridinyl) ligand with a 60° bite angle and ZnII ions. The direct self-assembly of G2 and G3 triangles by mixing organic ligands and ZnII , however, only generated a mixture of G1 and G2, as well as a trace amount of insoluble polymer-like precipitate. Therefore, a modular strategy based on the connectivity of ⟨tpy-Ru2+ -tpy⟩ was employed to construct two metallo-organic ligands for the assembly of G2 and G3 Sierpiński triangles. The metallo-organic ligands LA and LB with multiple free terpyridines were obtained through Suzuki cross-coupling of the RuII complexes, and then assembled with ZnII or CdII to obtain high-generation metallo-triangular architectures in nearly quantitative yield. The G1-G3 architectures were characterized by NOESY and DOSY NMR spectroscopy, ESI-MS, TWIM-MS, and transmission electron microscopy.

Metallo-Organic Ligand Designing Road for Constructing the First-Generation Dendritic Metallotriangle

Three approaches have been carefully examined in order to develop a terpyridine-based dendritic metallotriangle: (1) direct self-assembly of two types of organic polyterpyridines with metal ions; (2) assembly of flexible metallo-organic ligands containing two uncomplexed free terpyridines with a possible 60°-V-shaped orientation; (3) assembly of functionalized metallotriangles possessing a fixed 60°-bent uncoordinated bisterpyridine. Only the third approach has successfully given rise to the desired first-generation dendritic metallotriangle. Structural characterization was accomplished by NMR, ESI-TWIM-MS, and AFM.

Highly Stable Spherical Metallo-Capsule from a Branched Hexapodal Terpyridine and Its Self-Assembled Berry-type Nanostructure

Discrete spherical metallo-organic capsules at the nanometer scale, especially those constructed from unique building blocks, have received significant attention recently because of their fascinating molecular aesthetics and potential applications due to their compact cavities. Here, the synthesis and characterization of a hexapodal, branched terpyridine ligand are presented along with the nearly quantitative self-assembly of the resulting tetrameric metallo-nanosphere. This metallo-nanosphere exhibited four quasi-triangular and six rhombus-like facets, all of which were made by the same hook-like bis-terpyridine. Collision-induced dissociation experiments were done to investigate overall stability. The metallo-architecture and host-guest chemistry were investigated with coronene and fully characterized by 1D and 2D NMR, ESI-MS, and transmission electron microscopy. Furthermore, this metallo-nanosphere was observed to hierarchically self-assemble into berry-type structures in an acetonitrile/methanol mixture, by virtue of counterion-mediated attractions. The functional molecular metallo-nanosphere presented here expands the reach of terpyridine coordination systems into molecular containers and other model systems.

Terpyridinyl dibenzo[b,d]furan and dibenzo[b,d]thiophene based tetrameric bismetallo-macrocycles

Novel dibenzo[b,d]thiophene and dibenzo[b,d]furan-based bisterpyridine ligands have been synthesized and used to create unique metallomacrocycles. Direct self-assembly between the bisterpyridine ligands and Fe2+ led to a mixture containing multiple homo-metallomacrocycles. However, utilizing the robust Tpy(TpyRu2+Tpy)Tpy ligands, the metallo-organic ligands, coordination with Fe2+ resulted in the pure tetrameric bismetallo-macrocycles. Structures were characterized by 1H-NMR, COSY-NMR, DOSY-NMR, ESI-TOF-MS and UV/vis spectra.

Truncated Sierpiński Triangular Assembly from a Molecular Mortise–Tenon Joint

The amalgamation of different components into a giant and intricate structure that makes quantitative and spontaneous assembly through molecular design is indispensable but challenging. To construct novel metallo-supramolecular architectures, here we present an architectural design principle based on multicomponent self-assembly. Using a carefully designed hexatopic terpyridine-based metallo-organic ligand (MOL), [Ru2T2K], we report on the formation of supramolecular trapezoid Zn5[Ru2T2K]V2, hollow hexagon Zn15[Ru2T2K]3K3, and giant star-shaped supramolecule Zn18[Ru2T2K]3[Ru2X2V]3, all of which were assembled by one-pot, nearly quantitative assembly of [Ru2T2K] with the ditopic 60°-directed bisterpyridine V, tetrakisterpyridine K, and MOL [Ru2X2V], respectively. The complementary ligands were selected on the basis of the size- and shape-fit principles, actually similar to the mortise-tenon joint that aligns and locks the two complementary wood components. This strategy is expected to open the door to sophisticated designer supramolecules and nonbiological materials. The multivalent connections within the mutual ligands give rise to the formation of stable assemblies, which are unambiguously characterized by NMR, ESI-MS, TWIM-MS, and TEM analyses.