Conformationally Switchable Molecular Trefoil Knot Assembled From 2,6-Bis(1,2,3-triazol-4-yl)pyridine (btp) Building...

We report an efficient lanthanide-template synthesis of a conformationally switchable molecular trefoil knot assembled from three 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) ligand strands. Coordination of Lu³⁺ organizes three btp building blocks into a trimeric circular helicate that, upon subsequent ring-closing olefin metathesis, gives a trefoil knotted coordination complex in 73% yield over two steps. Subsequent demetalation with tetraethylammonium fluoride quantitatively affords the corresponding metal-free 87-atom-loop trefoil knot. The metal-coordinated and metal-free knots were characterized by NMR spectroscopy, high-resolution mass spectrometry, and single-crystal X-ray diffraction. The metalated and metal-free knots adopt substantially different conformations to each other, in both solution and the solid state. In the Lu³⁺-bound knot the btp units are directed inward to coordinate the metal center, with the strand conformation further stabilized by pyridine-naphthalene π-stacking. In the metal-free knot the btp motifs are rotated outward, with the conformation stabilized by triazole C-H···O hydrogen bonding and naphthalene-naphthalene π-stacking. Reversible metalation and demetalation cleanly interconverts the two knot conformations, establishing btp building blocks as a simple and versatile platform for responsive entangled or woven molecular topologies.