Synthesis And Hierarchical Self-Assembly Of Supramolecular Structures Based On Terpyridine Ligands

Supramolecular self-assembly is widespread in nature,which can gradually assemble components together through non-covalent interactions and build complex structures by employing hierarchical self-assembly strategies.Inspired by nature,hierarchical self-assembly strategies have been extensively studied to construct increasingly complex and precise supramolecular structures.Coordination-driven self-assembly of metallosupramolecular architectures with well-defined shapes,sizes,and geometries and diverse structures have been proven to be ideal platform to construct complex supramolecular hierarchical self-assembly systems.Among many organic ligands,2,2':6',2"-terpyridine(tpy),as a tridentate chelating ligand with the advantages of high coordination density and strong coordination ability,have been widely used for constructing precise,controllable,and complex supramolecular structures.However,the steric hindrance created by the vertical coordination of terpyridine with transition metal ions reduces the non-covalent interactions between discrete metallosupramolecules based on terpyridine.Therefore,it is still a great challenge to utilize discrete terpyridine-based supramacromolecules to obtain hierarchical self-assembly structures with controllable shape and size.In this thesis,the effects of hydrophilic/hydrophobic,?-?interactions and electrostatic interactions on the hierarchical self-assembly behavior of terpyridine-based metallosupramolecular structures were studied from the appropriate structural design and the introduction of non-covalent interactions.The research content of the thesis is divided into the following four parts:Chapter 1 The synthesis and hierarchical self-assembly of coordinated supramolecular structures are outlined.Based on the current challenges in the construction of supramolecular structures and the development of hierarchical assemblies,the topic of this thesis is proposed.Chapter 2 We designed and synthesized 5-modified tritopic asymmetric ligands LA and LB,under the premise of verifying the high coordination selectivity of the terpyridine ligands asymmetrically modified at the 5-and 4-positions.After coordination with Zn(II),the concave prisms Zn9LA6 and Zn6LB4 were obtained and characterized by NMR and mass spectrometry.In the obtained concave prism structure,the selective complementary coordination moiety is precisely designed in the cave of the structure,avoiding the influence of<tpy-Zn²⁺-tpy>steric hindrance on the hierarchical assembly.Driven by hydrophobic interactions,Zn9LA6 and Zn6LB4exhibited hierarchical self-assembly morphologies of hollow ring structure and nanowire,respectively,in the mixed solution of DMF and THF.When the polarity of the solvent was reduced,Zn9LA6 and Zn6LB4 exhibited sheet-like and rod-like structures.Zn6LB4 was assembled into well-aligned nanowires on the surface of highly oriented pyrolytic graphite(HOPG)and characterized by scanning tunneling microscopy(STM).Factors such as the shape of the discrete metallosupramolecules,the distribution of alkyl chains,the polarity of solvent,and different substrates all affect the hierarchical assembly behavior of metallosupramolecules.The work in this chapter demonstrates that the unique design of structure and the introduction of hydrophobic interactions can controllably tune the hierarchical self-assembly behavior.Chapter 3 On the basis of the work in Chapter 2,we introduced alkyl chains with different lengths,hydrophilic chains,and pyrazine units with easy?-?stacking in the structural design.We designed and synthesized the tetratopic terpyridine ligands LA,LB,and LC containing pyrazine units.The ligands were assembled with Zn(II)to obtain triangular prism structures SC,SD and SO.The expected triangular prism structures were characterized by NMR and mass spectrometry.In the triangular prism structure,the terpyridine coordination part is designed at the orthogonal position to the pyrazine unit,which avoids the influence of the steric hindrance caused by the octahedral coordination<tpy-Zn²⁺-tpy>moiety on the hierarchical assembly.Driven by hydrophobic and?-?interactions,SC self-assembles into helical nanowires.Based on the structure of SC,SD only increases the length of the alkyl chains.Driven by the enhanced hydrophobic interactions,SD hierarchically assembles into well-arranged 2D nanosheets.Finally,the effects of hydrophilic,hydrophobic,and solvent on the hierarchical assembly behavior were investigated by comparing the triangular prism SC and SO with modified hydrophilic and hydrophobic chains,respectively.The research in this chapter shows that in the presence of multiple non-covalent interactions,the hierarchical self-assembly behavior of terpyridyl precise structures can be regulated by adjusting the relative strength of the force.Chapter 4 Based on the work in the previous two chapters,we propose a strategy to control the ordered arrangement of metal-organic complexes by utilizing the electrostatic interaction between large anion clusters and metal-organic complexes with positive charges,solving the problem that the large steric hindrance of the<tpy-Zn²⁺-tpy>moiety makes two-dimensional supramolecules difficult to orderly stack.We designed and synthesized a series of complexes[Zn3LA3][Mo6O19]3,[Zn3LB3][Mo6O19]3,[Zn3LC3][Mo6O19]3 and[Zn3LD3][Mo6O19]3 obtained by electrostatic assembly of triangular metal rings and polyoxometalate TBA2[Mo6O19].The structure and hierarchical assembly morphologies of the composites were characterized by NMR,mass spectrometry,transmission electron microscopy(TEM)and scanning electron microscopy(SEM).We successfully cultivated and obtained the X-ray crystal structure of the composite[Zn3LC3][Mo6O19]3,which exhibited the expected regular three-dimensional structure.Due to the existence of micropores inside the composites,these four composites have different adsorption capacities for the vapors of benzene,toluene,and cyclohexane.The research in this chapter shows that the large anion clusters can effectively avoid the steric hindrance caused by terpyridine,and their negative charges are conducive to the construction of ordered complexes.