The Future of Structural Chemistry Nucleates in the Present

A personal view of nearly four decades of structural chemistry is presented. The rise of molecular crystal engineering as an independent cross-disciplinary field of research at the intersection of crystallography with supramolecular chemistry and solid-state reactivity is discussed in light of the development of theoretical and instrumental tools and the need for novel molecular materials. The exchange of ideas and experience within the structural chemistry community has played a fundamental role in reaching the present high level of understanding of the factors that control crystal formation and stability. Crystal-oriented synthetic strategies, including solvent-free mechanochemical methods, have been developed, as well as screening methods and computational approaches. Some drawbacks and limitations are also discussed. The wealth of multiple crystal forms, from single-molecule crystals to solvates, co-crystals, salts and ionic co-crystals, and their polymorphs, is both an open challenge to the crystal engineering paradigm and a source of discovery and innovation.