A new non-covalent interaction: the nido cage-···nido cage- interaction

Carboranes are boron–carbon clusters with important applications in fields of materials, catalysis, pharmaceuticals, etc. However, the non-covalent interactions that could determine the solid-state structures and properties of such boron clusters have been rarely investigated. Herein, inspired by the coordinate bond in metallacarborane or ferrocene, the boron cluster-based non-covalent interaction (denoted as cage^–···cage^– interaction) between two nido-carborane clusters was successfully realized by using a pyridinium-based molecular barrier. The X-ray diffraction studies uncover that the cage^–×××cage^– interaction has a contacting distance of 5.4-7.0 Å from centroid to centroid in the systems reported here. Theoretical calculations validate the formation of the non-covalent interaction and disclose its repulsive bonding nature that is overcome thanks to the positively charged pyridinium-based framework. Interestingly, such bulk crystalline materials containing the cage^–···cage^– interaction show relevant properties such as full-color absorption in the visible light range and important  photothermal effect, which are absent for the control compound without carboranes. This study may offer fundamental insights into the boron cluster-based non-covalent interactions and open a new research avenue to rationally design boron cluster-based materials. Finally, we have computationally shown that this π^–···π^– interaction is also possible in classical organic systems.

Synthesis of the clusters were done by the group of Prof. Hong Yan in Nanjing University and calculations were performed in the IQTCUB institute by Prof. Jordi Poater and in the DiMoCat group by Prof. Miquel Solà.

The paper has been highlighted by the Spanish Biophysical Society (https://sbe.es/paperhighlights-nov2021-2/).

The paper can be read in JACS Au journal through the following link:

https://pubs.acs.org/doi/10.1021/jacsau.1c00348