Dynamic Interconversion and Induced-Fit Guest Binding with Two Macrocycle-Based Coordination Cages

Abstract

We report the syntheses and host–guest chemistry of two interconvertible coordination cages, Pd2L2 and Pd1L1, from a dynamic macrocycle ligand (L) and a cis-blocking (tmen)­Pd­(NO3)2 (tmen = tetramethylethylenediamine) unit (Pd). The water-soluble macrocyclic L, which can bind various polycyclic aromatic hydrocarbon (PAH) guests in its cis-conformation, was constructed via four pyridinium bonds between two 2,4,6-tri­(4-pyridyl)-1,3,5-triazine [TPT] panels and two p-xylene bridges. We selectively formed each cage either by changing the reaction concentration/solvent/temperature or through induced-fit guest encapsulation, while direct assembly of L and Pd resulted in a mixture of Pd2L2 and Pd1L1 in equilibrium. X-ray structures of the free ligand and the host–guest complexes confirmed the induce-fit adaptive changes in the ligand’s conformation and the cage’s cavity. This work demonstrates a useful strategy for designing multistimuli-responsive supramolecular hosts by coordination self-assembly with macrocyclic ligands featuring rich conformational freedom.

Formation of an Unusual Pseudo-Square Planar-Induced Mercury(II) Dimeric Complex

“…Macrocyclic ligands play a critical role in supramolecular coordination chemistry due to their specific ability to selectively bind and self-assemble with particular metals or guest molecules [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. This selectivity is the result of their unique structure, which forms a cyclic cavity that can accommodate specific species.…”