Nature Chemistry ( IF 21.8 ) Pub Date : 2020-12-14 , DOI: 10.1038/s41557-020-00594-x David A Leigh 1, 2 , Jonathan J Danon 2 , Stephen D P Fielden 2 , Jean-François Lemonnier 2 , George F S Whitehead 2 , Steffen L Woltering 2
Current strategies for the synthesis of molecular knots focus on twisting, folding and/or threading molecular building blocks. Here we report that Zn(ii) or Fe(ii) ions can be used to weave ligand strands to form a woven 3 × 3 molecular grid. We found that the process requires tetrafluoroborate anions to template the assembly of the interwoven grid by binding within the square cavities formed between the metal-coordinated criss-crossed ligands. The strand ends of the grid can subsequently be joined through within-grid alkene metathesis reactions to form a topologically trivial macrocycle (unknot), a doubly interlocked [2]catenane (Solomon link) and a knot with seven crossings in a 258-atom-long closed loop. This 74 knot topology corresponds to that of an endless knot, which is a basic motif of Celtic interlace, the smallest Chinese knot and one of the eight auspicious symbols of Buddhism and Hinduism. The weaving of molecular strands within a discrete layer by anion-template metal–ion coordination opens the way for the synthesis of other molecular knot topologies and to woven polymer materials.