JACS: self-assembly of tripyridine to form fractal geometry

The word "geometry" is not new to most middle school educated people In middle school, we were exposed to some straight lines, triangles, squares, circles or more complex geometric shapes composed of them However, there are a lot of irregular objects in nature that are difficult to describe with traditional geometry, such as clouds in the sky, towering trees and so on The shapes of these objects can not be described by simple European geometry To solve this problem, some scholars put forward the concept of fractal geometry The geometry with fractal characteristics is usually self similar, that is, its components are similar to the shape of the whole reduced Since it was put forward in 1970s and 1980s, fractal theory has been gradually applied to various fields including mathematics, physics, chemistry, astronomy and meteorology, geology, materials science, etc Figure 1 Fractal geometry with different iterations (photo source: J am Chem SOC.) recently, Professor Li Xiaopeng of the University of South Florida, Professor Xu Bingqian of the University of Georgia, Associate Professor Li Xiaohong of Suzhou University and Professor Wang Ming of the Department of chemistry of Jilin University joined hands with the help of TPY ）Through self-assembly, a variety of supramolecular fractal structures are constructed (Fig 1) The study of constructing fractal structure by chemical means has a long history At present, the surface self-assembly can avoid some complex organic synthesis, but the products are basically mixtures with different iterations In addition, although metal supramolecular assembly can obtain pure products, there are still some problems: due to the limitations of design, synthesis and separation, the existing technology can not obtain more complex fractal geometry The research team designed a kind of polygon fractal geometry to solve this problem Through the complexation of tripyridine with zinc ion (Zn 2 +) and ruthenium ion (Ru 2)), the fractal geometry of up to five iterations was prepared This achievement was published in the Journal of the American Chemical Society (DOI: 10.1021 / JACS 8b05530) under the title of "self assembly of supramolecular fragments from generation 1 to 5" Figure 2 Structure of ligands La, l and LD (top) and construction method of G1-G5 (bottom) (photo source: J am Chem SOC.) in order to precisely control the structure of the figure, the author selected triphenylamine as the core of the structure unit, and obtained ligands La, l and LD with different tripyridine units through Sonogashira coupling reaction (Figure 2 Above) Among them, La has two tripyridine units, l has six, and LD has four After these ligands are obtained, the construction of fractal geometry is relatively simple: two la molecules and two Zn2 + can be assembled into the simplest fractal geometry G1; similarly, G4 is constructed by six LD and 12 Zn2 +; G2, G3 and G5 However, they are obtained by simply mixing different proportions of ligands and metal ions, so the authors can only obtain them by synthesizing intermediates first and then combining them with corresponding Zn2 + Taking G5 as an example, the author first complexes one LA with two ru2 +, then with one l to get Le, and then assembles six LES with 12 Zn2 + to form G5 (Figure 2 below) Fig 3 G1 - G5 electrospray ionization mass spectrometry, travelling wave ion migration mass spectrometry and nuclear magnetic DOSY spectrogram (source: J Am Chem Soc.) After initial obtaining these fractal geometric patterns, the author has made structural characterization Because of the complicated graphic structure, only the relative auxiliary information can be provided by nuclear magnetic hydrogen spectrum and carbon spectrum The molecular structure calculated by computer simulation can only show that these ligands and ions may form these images, but can not give relatively reliable results Therefore, the structures of these structures were characterized by mass spectrometry, including electrospray ionization mass spectrometry (ESI-MS) and traveling wave ion mobility mass spectrometry (TWIM-MS) The results show that the mass spectrum data can correspond to the theoretical values one by one In addition, the authors have also carried out the NMR DOSY experiments on the synthesized fractal geometry, and the results show that they do have a relatively single structure Highlight of this paper: the author synthesized complex fractal geometry by using the characteristics of tripyridine, which not only can be obtained by simple ligand replacement, but also has a high degree of oneness Full text author: Lei Wang, ran Liu, Jiali Gu, Bo song, Heng Wang, Xin Jiang, kerenzhang, Xin Han, Xin Qi Hao, Shi Bai, Ming Wang, Xiaohong Li, Bingqian Xu, and xiaoopeng Li