Understanding the Effect of Solvents on Crystallization of the Same Chelate: Crystal Structures in Structural Chemistry

To help senior students better understand the chapter on crystal structures in the course Fundamentals of Structural Chemistry, it is critically important to improve their skills in single crystal growth, handling and solving X-ray crystal data, and interpreting small molecule 3D structures, including molecular packing, space groups, and polymorphism. These skills will serve them well in many areas of practical chemistry and biochemistry. To comprehend the key role of solvents in the construction of 3D structures, described here are three typical crystals of [CoLCl]Cl (where L is N,N′,N″,N‴-tetra(2-hydroxy-3-methoxy-5-methylbenzyl)-1,4,7,10-tetraazacyclododecane) grown in different solvents (solvents are methanol, methanol + water, and methanol + dimethyl sulfoxide for crystals 1, 2, and 3, respectively). The crystal structures were interpreted using single crystal XRD measurements, and the structures were refined by the students using Olex2 software to obtain solvent dependent polymorphic 3D crystal structures. The crystal system we have described serves as an excellent test-bed with excellent practical simplicity and high crystal yields that allow students to improve their understanding of the key role of solvents in the solvent-dependent molecular packing of 3D crystals. The combination of crystal growth and practical structural refinements really helps students to reinforce their theoretical learning from structural chemistry through these laboratory practices. By completing these practical experiments, students can learn how to approach crystal structure interpretation and experimental considerations and to extract structure–solvent relationships. Collectively, our work remedies the shortage of practical crystallographic courses across many university syllabuses and helps students to build themselves a toolkit for elementary but practical structure determination they can reinforce, advance, and use in the future.