Chemists weave molecular fabric

Chemists link molecules together all the time, but interlacing them like threads in fabric presents a bigger challenge. Now, researchers in David A. Leigh’s lab at the University of Manchester have created the first 2-D fabric made of molecules woven together. The molecular fabric can separate large ions from smaller ones. It also has unique properties that could make it useful for other applications: the woven material is twice as stiff as the unwoven linear polymer it’s made of and tears along well-defined lines, just like a textile.

“Knotting and weaving have always had great technological impact for humans,” Leigh says, noting that the invention of knots and weaves helped humans create weapons, tools, nets, and cloth. “Who’s to say it won’t be the same for molecular structures?”

The molecular fabric project arose from his lab’s work tying molecular knots, says Leigh. To create the core of a particular molecular knot, Leigh and coworkers start with iron ions and tetrafluoroborate anions, which serve as templates to create a grid made from six entwined compounds. Leigh says the chemists tied things up using olefin metathesis to covalently link the grid’s dangling ends (Nat. Chem. 2020, DOI: 10.1038/s41557-020-00594-x).

During that project, they discovered that the grids crystallized in layers, where each grid was like a black square in a chess board. The dangling ends could reach from square to square but not from layer to layer, which made the chemists realize they could make single layers of woven molecular fabric by linking the dangling ends from one grid to four others via disulfide bonds. Removing the template ions leaves behind a wholly organic molecular fabric (Nature 2020, DOI: 10.1038/s41586-020-3019-9).

Chemists have made woven 3-D structures before, but this is the first example of a woven 2-D material. It’s only 4 nm thick, even though its area measures hundreds of µm across. Craig Hawker, who specializes in materials and molecular engineering at the University of Santa Barbara, points out that Leigh’s group makes the ultrathin, macroscopic films using robust and simple assembly conditions.

“This work shows how an intelligent combination of organic and polymer chemistry with supramolecular chemistry results in an impressive step towards conquering literally a new dimension for synthetic chemistry,” says Dieter Schlüter, an expert in novel macromolecular structures at the Swiss Federal Institute of Technology (ETH) Zurich, in an email. “This is thrilling and likely encourages others to think along similar lines.”