Scheme 4.

Synthesis of a trefoil knot by the circular helicate approach. a) A single lanthanide ion entwines three 2,6‐diamidopyridyl ligand strands 14 in its coordination sphere, thereby forming a trefoil knot upon connection of the ligand end groups. The achiral precursor 14 a yields a racemic mixture of the two enantiomers of trefoil knot Ln15 a. The use of C ₂‐symmetric ligand 14 b gives enantiopure trefoil knot Ln15 b. b) X‐ray crystal structure of enantiopure trefoil knot Ln15 b.72, 73