Crystal packing can be arranged to leave gaps for adsorption of and interaction with guest molecules of interest, e.g., for functional materials. Adjustable stoichiometries are fairly common for inorganic materials such as metal alloys. Organic equivalents have been restricted to solid solutions of molecules with similar sizes, shapes and natures.
Anthony Davis and co-workers, University of Bristol, UK, previously showed that steroidal ureas can be crystallized so that the functional group of the urea building block is located inside channels in the material. They now demonstrate that these materials can also be formed from mixtures of ureas to create an organic alloy. The functional groups of each urea can be varied without changing the overall structure. This approach allows the nanoporous channels to accommodate a much wider variety of molecular components. In this way, continuous variation of the crystal compositions and properties becomes possible. The channels in these organic alloys are chiral and can accept guest molecules which allows doping with chromophores, for example.
The tunability and doping capacity of these materials could see them used for sensing, catalysis, or flow control.