Molecular rectangles adjust their shape while keeping their strong framework
Chemists assembled electrically neutral molecular rectangles whose strong metal–carbon connections survived changes in geometry. Different guest molecules associated with the outer walls and accompanied expansion or contraction in crystal structures. The peer-reviewed laboratory study separates building the framework from locking it into place, allowing its dimensions to be adjusted during assembly.
Science··Midday
Guest molecules accompany opposing changes in crystal geometry
Electrically neutral molecular rectangles adjusted their geometry when other molecules associated with their outer walls. With pyrene, a flat aromatic molecule, a representative rectangle contracted along one direction and widened along the other. An electron-accepting guest accompanied the opposing change. The palladium–carbon connections holding the framework together survived. These observations compare crystal structures in the solid state; a continuous cycle of movement was not demonstrated.[1]
Assembly separates shaping from locking the framework
Strong metal–carbon bonds make persistent structures, but they also hinder the rearrangement that can correct a poorly assembled shape. The chemists separated their construction into stages. Geometrical information was established in the starting scaffold, polymeric intermediates were converted to discrete building blocks, and linkers then closed the rectangles. Changing the scaffold and its connecting components allowed length and width to be adjusted separately.[1]
Spectroscopy, mass measurements and single-crystal X-ray diffraction established the products’ identities and shapes. Their electrical neutrality removed the need for accompanying counterions, reducing interference with interactions under investigation. One representative compound remained intact for more than a month in solution. Colour and spectral changes supplied additional evidence of guest association in solution, alongside the separate crystallographic comparisons that revealed how the framework accommodated different external contacts.[1]
