Coordination-driven self-assembly of a molecular figure-eight knot and other topologically complex architectures

Li-Long Dang,Yue-Jian Lin,Wei-Long Shan,Guo-Xin Jin,Zhen-Bo Sun,Zhen-Hua Li

doi:10.1038/s41467-019-10075-6

Abstract

Over the past decades, molecular knots and links have captivated the chemical community due to their promising mimicry properties in molecular machines and biomolecules and are being realized with increasing frequency with small molecules. Herein, we describe how to utilize stacking interactions and hydrogen-bonding patterns to form trefoil knots, figure-eight knots and [2]catenanes. A transformation can occur between the unique trefoil knot and its isomeric boat-shaped tetranuclear macrocycle by the complementary concentration effect. Remarkably, the realization and authentication of the molecular figure-eight knot with four crossings fills the blank about 41 knot in knot tables. The [2]catenane topology is obtained because the selective naphthalenediimide (NDI)-based ligand, which can engender favorable aromatic donor-acceptor π interactions due to its planar, electron-deficient aromatic surface. The stacking interactions and hydrogen-bond interactions play important roles in these self-assembly processes. The advantages provide an avenue for the generation of structurally and topologically complex supramolecular architectures.

Highlights

Over the past decades, molecular knots and links have captivated the chemical community due to their promising mimicry properties in molecular machines and biomolecules and are being realized with increasing frequency with small molecules
A number of trefoil knots (31)22–28 have been prepared to date, there are few works providing an insight into the transformation between monomeric macrocycles, molecular knots and links
The stacking interactions and hydrogen bonding interactions can be considered as the driving force for the formation of trefoil knot and figure-eight knot, while a [2] catenane was formed by the combination of another planar, electrondeficient aromatic edge unit (E4) with L1

Summary

Introduction

Molecular knots and links have captivated the chemical community due to their promising mimicry properties in molecular machines and biomolecules and are being realized with increasing frequency with small molecules. A number of trefoil knots (31) have been prepared to date, there are few works providing an insight into the transformation between monomeric macrocycles, molecular knots and links. A careful study of single-crystal structure of the knot indicates that the molecule can adopt various forms by altering its conformation, including the reduced form with four crossings and the fourfold symmetry form with eight crossings (Fig. 1). These synthesized knots and links are unambiguously characterized by NMR spectroscopy, ESI-MS, and single-crystal X-ray diffraction analysis. Density functional theory (DFT) calculations are used to provide insight into the formation of the [2]catenane and trefoil knots

Methods

Results

Conclusion