s-Block metal ions induce structural transformations between figure-eight and double trefoil knots

Abstract

The formation of two types of heterobimetallic molecular knots, double trefoil and trefoil knots, induced by s-block metal ions, is presented. Coordination of K⁺, Ca²⁺, Sr²⁺ or Ba²⁺ ions with amide groups plays a crucial role in the formation of these trefoil knots. Remarkably, the reversible topological transformation between a figure-eight knot and double trefoil or trefoil knots can be induced by coordination of s-block metal ions to amide groups. X-ray crystallographic data and NMR experiments support the structural assignments.