Abstract
This paper discloses coordination approaches to well-defined organic structures including macrocycles, a three-dimensional cagelike compound, and [2] catenanes. These supramolecules self-assembled from (en) Pd(NO3)2 (1, en = ethylenediamine) and appropriate polypyridyl-substituted ligands. Treatment of 1 with 4, 4′-bipyridine (2), for example, gave macrocyclic tetranuclear Pd(II) complex [(en) Pd(μ-2)]4(NO3)8 quantitatively, while macrocyclic dinuclear Pd(II) complexes assembled from 1 and flexible ligands such as PyCH2CH2Py (Py =4-pyridyl). From tridentate ligand 1, 3, 5-(PyCH2)3C6H3 and 1 in 2 : 3 ratio, on the other hand, a three-dimensional cagelike compound assembled in high yields only in the presence of certain types of guest molecules, providing an entire model for 'induced-fit'. The coordination approach made it possible to interlock two apparently continuous molecular rings : i.e., a macrocycle assembling from 1 and 1, 4-(PyCH2)2C6H4 was found to be in equilibrium with its catenated dimer, and polar medium strongly pushed the equilibrium toward the catenane up to >99 : 1 ratio.
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