Making Crystals from Crystals: a solid-state route to the engineering of crystalline materials, polymorphs, solvates and co-crystals; cosiderations on the future of crystal engineering

Making crystals by design is the paradigm of crystal engineering. The main goal is that of obtaining and controlling the collective properties of a crystalline material from the convolution of the physical and chemical properties of the individual building blocks (whether molecules, ions, or metal atoms and ligands) with crystal periodicity and symmetry. Crystal engineering encompasses nowadays all traditional sectors of chemistry from organic to inorganic, organometallic, biological and pharmaceutical chemistry and nanotechnology. The investigation and characterization of the products of a crystal engineering experiment require the utilization of solid state techniques, including theoretical and advanced crystallography methods. Moreover, reactions between crystalline solids and/or between a crystalline solid and a vapour can be used to obtain crystalline materials, including new crystal forms, solvates and co-crystals. Indeed, crystal polymorphism, resulting from different packing arrangements of the same molecular or supramolecular entity in the crystal structure, represents a challenge to crystal makers.