Spontaneous assembly of a hinged coordination network

THE field of supramolecular chemistry has advanced to a stage at which it is possible to select building blocks that will self-assemble into structures with specific network topologies^1-3. This makes possible the rational design and synthesis of molecular solids with potentially interesting properties. Here we report the construction of open, hinged networks from molecular building blocks. This class of materials has been predicted to exhibit unusual mechanical properties, including auxetic behaviour (negative Poisson's ratio) and negative coefficients of thermal expansion^4-6. Our approach relies on the notion that rigid organic molecules of high symmetry will adopt one of only a few possible structures when linked via hydrogen bonds or coordination to metals^7-9. We use trigonal ligands to make networks joined at the vertices by metal ions; the resulting networks are homeotypic¹⁰ with the honeycomb-like AlB₂ and the hinge-like ThSi₂ phases. The hinge-like network has channels of inner diameter 15 Å, within which included molecules can be exchanged while the framework remains intact. We have not yet determined whether this material is auxetic.