Self-Assembly of Polyhedral Coordination Cage Complexes with Bis-Bidentate Ligands


Student thesis: Doctoral Thesis

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  • Jing YANG


Awarding Institution
Award date5 Dec 2016


This thesis concerns the structural and host-guest properties of polyhedral coordination cages based on different bis-bidentate ligands having m-xylene as bridge. A general introduction of coordination cages that are previous research around the world are presented in Chapter 1.

Chapter 2 describes new M8Lim12 cubic cages of Mn, Zn and Cd. These cages can be easily synthesized by self-assembly with inexpensive readily available starting materials. The captured anion of [Cd8Lim12](OTf)16 cage is exchangeable with SbF6, ClO4, Tf2N– and NO3 anions, in which NO3 anions could exchange with the six exterior anions first and then with the encapsulated TfO anion. But with additional TsO anions, it is clear that there are exterior anions on the surface of the cage which affect the anion exchange and further stop the exchange. The captured PF6 anion of [Zn8Lim12](PF6)16 cage can also be displaced by SbF6 and Tf2N anions. And additional NO3 anions could exchange with the six PF6 anions at the centers of the six faces of the cage and then slow down the PF6 anion exchange.

Chapter 3 describes two different cages [Cd12Lpy18](OTf)24 and [Cd8Lpy12](OTf)16 that are self-assembled from the same starting materials. The hexagonal prism is a crystallization product and slowly rearranges to the cube. The cube is formed in minutes after Cd(OTf)2 is mixed with Lpy. When the solution of the cubic complex is recrystallized by diffusing isopropyl ether, the hexagonal prism is generated again. These changes appear to show a cage-to-cage interconversion in solution at room temperature.

Since there is no enthalpic change of bond strengths, the conversion from [Cd12Lpy18](OTf)24 to [Cd8Lpy12](OTf)16 becomes entropically more positive driving the formation of smaller cage. The solution studies reveal that addition of NO3 and OTs anions could accelerate the conversion from hexagonal prism to cube, but PF6 and SbF6 anions could slow it down. The anions at the surface of the cage play an important role in affecting the structural arrangement.

Chapter 4 described the preparation of M12Lth18 hexagonal prismatic cages of Mn, Zn and Cd by self-assembly using thiazolyl-imine or pyridyl-imine ligands, both of which have an m-xylene-bridge. Crystal structures of Cd12Lth18(PF6)24, Cd12Lth18(SbF6)24 and Zn12Lpy18(SbF6)24 were obtained. There are three or four different species of hexagonal prisms capturing different anions during the processes of anion exchange. The captured anions of Cd12Lth18(OTf)24 cage are exchangeable with SbF6 and PF6 in which there exists three kinds of hexagonal prisms capturing different anions. The captured anions of Cd12Lth18(PF6)24 cage are exchangeable with SbF6 and ClO4 in which there exists four kinds of hexagonal prisms. Dynamic metal exchange and ligand exchange processes were directly demonstrated which further confirmed that the exchange of anions takes place through the faces of the hexagonal prisms.