This project is founded on the premise that a new generation of composite materials can be designed from first principles using the concepts of crystal engineering and an understanding of how complementary topologies of molecular networks can be exploited. In principle, the following objectives are feasible and anticipated outcomes of the proposed research: a high degree of control over structure and composition even when involving very different chemical components; bulk properties that arise from both components of the composite solid. Preliminary studies have demonstrated that composite structures can be sustained by two classes of open framework 2D coordination polymers (square grids and, as illustrated alongside, puckered rectangular grids) that coexist with noncovalent networks that are formed by aromatic stacking interactions.
The primary objective of the proposed research is to confirm the generality of the design concept and to expand it to a much wider range of architectures and molecular components. It is expected that a large number of new compounds will be generated since all new compounds will be prepared via self-assembly processes, i.e. one-pot reactions; multiple modular components. The structure, chemical and physical properties of a large number of new composite compounds will be determined as part of the proposed research.
Chemists have only recently applied the concepts of supramolecular synthesis and crystal engineering to generate new classes of coordination polymer and there has been a remarkable degree of success in terms of both design and properties. In particular, it has been demonstrated that the principles of self-assembly can be invoked to design novel 2D and 3D architectures from simple molecular building blocks and that the properties of these new structures can offer unprecedented degrees of porosity. Such structures have typically been based upon the cross-linking of transition metal-based nodes by "spacer" ligands. We propose to exploit some of these novel architectures in a different context: formation of close-packed composite materials that use the coordination polymer framework as a structurally rigid template. We also propose to increase the scale of existing and new architectures by using nanoscale building blocks and/or templates, including biomolecules.
We feel that the proposed research is relevant for both fundamental and applied reasons. From a fundamental perspective, design and prediction of structure of crystalline phases remains a challenge of the highest order. From a more applied perspective, the possibility of combining two very different physical properties in one pure phase is attractive and has already shown great promise. We cannot express the opportunity we face any better than by quoting Feynman as follows: "What could we do with layered structures with just the right layers? What would the properties of materials be if we could really arrange the atoms the way we want them? They would be very interesting to investigate theoretically. I can't see exactly what would happen, but I can hardly doubt that when we have some control of the arrangement of things on a small scale we will get an enormously greater range of possible properties that substances can have, and of different things that we can do." (Richard P. Feynman, December 29, 1959).
Biradha, K.; Domasevitch, K.; Moulton, B.; Seward, C.; Zaworotko, M.J. "Covalent and Noncovalent Interpenetrating Planar Networks in the Crystal Structure of n", Chem. Comm., 1327-1328, 1999.
Also featured in Chemical & Engineering News, July 26 1999, pp 10-11.
Zaworotko, M.J. "Superstructural Diversity in Two Dimensions: Crystal Engineering of Laminated Solids", Chem. Commun., 1-9, 2001.
Bourne, S.A.; Lu, J.; Mondal, A.; Moulton, B.; Zaworotko, M.J. "Self-Assembly of Nanometer-Scale Secondary Building Units into an Undulating Two-Dimensional Network with Two Types of Hydrophobic Cavity", Angew. Chem., Int. Ed. Engl.,40, 2111-2113, 2001.
Moulton, B.; Zaworotko, M.J. "From Molecules to Crystal Engineering: Supramolecular Isomerism and Polymorphism in Network Solids", Chemical Reviews, 101, 1629-1658, 2001.
Bourne, S.A.; Lu, J.; Moulton, B.; Zaworotko, M.J. "Coexisting covalent and noncovalent nets: parallel interpenetration of a puckered rectangular coordination polymer and aromatic noncovalent nets." Chem. Commun., 861-862, 2001.