Single-crystal-to-single-crystal Transformations for the Preparation of Small Molecules, 1D and 2D Polymers Single Crystals

The single-crystal-to-single-crystal (SCSC) transformation is a fascinating and valuable outcome of topochemical reactions. Not like the solution-state reactions, the movement and transformation of the molecule in single-crystal state is such a mysterious and attractive research topic. The molecular packing of the monomers prior to the reaction could provide many possibilities for the formation of complicated topological structures. The further reaction or polymerization in the single crystal state could realize the preparation of covalent complicated topological structures. In this review, we summarized six different types of organic reactions that could realize the SCSC conversion, namely [2 + 2], [4 + 4], and [4 + 2] photo-cycloaddition, dienes polymerization, acetylenes polymerization and topochemical azide-alkyne cycloaddition. The crystalline packing phases offer the possibility of significant advances in the crystal structure design. Some examples of 1D or 2D polymer single crystals realized by SCSC transformation were summarized subsequently.