Quantitative Formation of Catenanes from Rectangular Molecular Boxes

1 Quantitative Formation of Catenanes from Rectangular Molecular Boxes 

As discussed in the last section, the driving force for the self-assembly of cate-nane 13 is the efficient aromatic contact between two monomer rings. Therefore, we designed a rectangular molecular box 21 containing Pd(II)-pyridine coordinate bonds. 

A force field calculation predicted that this box would have an appropriate interplane separation (ca. 3.5 A) in the cavity. Therefore, two molecules of inorganic box 21 are expected to slide into a catenated dimer. In fact, when we combined 11 and ligand 22, we observed the formation of a single component, catenane 23 (Eq. 4) [29], 

Successful self-assembly of catenanes 23 and 25 and their remarkable stability imply that rectangular box structures for the component rings are very effective for catenation. Thus, we also designed the construction of rectangular frameworks from a set of 11 and two different ligands. Surprisingly, these three-component systems worked very well and we observed highly efficient three-component- 

The remarkable thermodynamic stability of catenane 28 overcame a combination problem which should arise in self-assembly from a larger set of components. At least, formation of three component rings 32-34 is possible because their thermodynamic stability is comparable. Nevertheless, catenane 28 self-assembled as a sole product. This result shows that, having an ideal van der Waals separation (3.5 A) in its framework, only rectangular box 34 can be stabilized by filling its cavity with another copy of itself. Actually, the efficient aromatic stacking of four 

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