1. What is the new discovery that you made?
Our research focused on how imidazolium salts containing halogen atoms bind anions in solution. We wanted to differentiate among various interactions: Halogen bonding, hydrogen bonding and anion-pi interactions. In the end, we could rule out any interaction between the anions and the aromatic surface of the halogen bond donors. Several experimental means (X-ray, calorimetry, NMR) showed that there is either pure halogen bonding in solution or mixed halogen / hydrogen bonding with equal strength. Experimentally, this is difficult to differentiate, but molecular dynamics simulations clearly preferred the latter option.
Cationic halogen bond donors like haloimidazolium salts contain – as the name suggests - halogen atoms, like iodine, which favor halogen bonding. Halogen bonding is quite a similar interaction to hydrogen bonding, but it is based on a halogen substituent instead of hydrogen. Therefore, the halogen atom tends to coordinate with electron rich species like anions. Since our compounds also feature other interactions, we needed to differentiate between them. This was possible only thanks to a mix of experimental and theoretical approaches.
2. What is its significance?
In the last years, an increasing number of applications of halogen bonding has appeared in the literature. It is expected that this will establish itself as a further tool in molecular recognition, anion transport, pharmaceutical applications and catalysis. Especially for the latter two, halogen bonding is likely to have a long-term impact on society, since it allows to control the action of drugs and the preparation of various chemicals. For example, the 2-haloimidazolium structure is as a versatile and strong halogen-bond donor that has gained applications in the fields of anion recognition and more recently in non-covalent organocatalysis.
3. Is this related to Solvation Science? If yes, how?
Similar to hydrogen bonding, halogen bonding is a core theme of solvation science. It´s an important interaction in solution and many of the applications of halogen bonding take place in solution. Thus, it is essential to systematically investigate how halogen bond donors interact with halogen bond acceptors as well as how the individual solvent molecules affect the binding strength of these Lewis acids. The RESOLV cluster in Bochum is the perfect scientific environment to pursue this.
Original Publication:
Schulz, N., Sokkar, P., Engelage, E., Schindler, S., Erdelyi, M., Sanchez-Garcia, E. and Huber, S. M. (2018), The Interaction Modes of Haloimidazolium Salts in Solution. Chem. Eur. J..