Self-Assembly of Molecular Figure-Eight Knots Induced by Quadruple Stacking Interactions

Molecular figure-eight
knot (notation: 41) is extremely
rare and presents great synthetic challenge due to its essentially
complicated entanglement. To solve this synthetic problem, a quadruple
stacking strategy was developed. Herein, we report the efficient self-assembly
of figure-eight knots induced by quadruple stacking interactions,
through the combination of four carefully selected naphthalenediimide
(NDI)-based pyridyl ligands and Cp*Rh building blocks bearing large
conjugated planes in a single-step strategy. Notably, slight size
adjustment of the Cp*Rh units was found to affect the stability of
the figure-eight knots in methanol. Additionally, reversible structural
transformations between these figure-eight knots and corresponding
metallorectangles could be achieved by concentration changes and solvent-
and guest-induced effects. X-ray crystallographic data and NMR spectroscopy
provide full confirmation of these phenomena.