| Discrete metal-organic cages with a certain shape,size and internal cavities are widely concerned due to their potential applications in molecular recognition,ion exchange,gas adsorption,catalysis,drug delivery and so on.However,the self-assembly process of metal-organic cages may be affected by many factors,resulting in different kinetics,thermodynamics or template-induced products,which have great potential to realize different functions.Among many factors,solvents,as the place where most cages exist,has a non-negligible influence on the structure of cages.Therefore,we focus on the influence of solvent on the configuration and composition of cages.We synthesized a banana-shaped ligand L1 bearing two amide groups and two pyridine segments symmetrically,and a metal-organic cage Pd2(L1)4(Cage 1)was constructed by combining L1 with Palladium.Cage 1 was used to study the influence of different solvents on the formation of different conformation.As a whole,cage 1 is more likely to exist in PM conformation in the big solvent molecules such as DMSO,DMF,and glycerol,while in the small solvent molecules such as water,acetonitrile and methanol,it tends to exists in PP/MM conformation.Subsequently,cage 2 and 3 were also successfully obtained by using chiral ligands L2 and L3,respectively.These cages showed the same result to the solvent effect as cage 1.Moreover,the longer ligand L4 was synthesized to study the influence of solvent in double cages.In acetonitrile,single cage Pd2(L4)4 was formed by coordination of the ligand L4 with Pd(CH3CN)4(BF4)2,and two of this cage can gradually dimerize to assemble the interpenetrated cage Pd4(L4)8.But in DMSO,only single cage exist.We referred that the entropy plays a key role in the process of the dimerization of cage,as solvent molecules would be released from the cavity.Therefore,the smaller volume of solvent molecules,the more favorable the formation of the interpenetrated cage. |
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