Intra-solid and inter-solid reactions of molecular crystals: a green route to crystal engineering

The thesis developed in this chapter is that reactions taking place between molecular solids or within molecular solids, or involving a molecular solid and a vapour, can be exploited to "make new crystals", which is the quintessence of crystal engineering. Processes that lead from a crystalline reactant, or mixture of reactants, to a crystalline product without the intervention of solvents will be discussed. The focus will be on solid-state reactions controlled primarily by supramolecular bonding, such as template cycloadditions, formation of inclusion compounds, reactions between molecular crystals via reassembling of non-covalent bonding, and formation of complexes and coordination compounds. It is argued that solvent-free methods, e.g. co-grinding or milling of molecular solids, or reactions of solids with vapours represent viable "green" routes for the preparation of novel molecular and supramolecular solids.