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

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

The aromaticity of boron clusters in the Front Cover of JACS!

The Journal of the American Chemical Society (JACS) features in its FRONT COVER the recently published article “Too Persistent to Give Up: Aromaticity in Boron Clusters Survives Radical Structural Changes”. The work has been carried out by Prof. Francesc Teixidor, Prof. Clara Viñas, and Dr. Ines Bennour of the Institute of Materials Science of Barcelona (ICMAB-CSIC), Prof. Jordi Poater at the University of Barcelona (previous DiMoCat member) and Sílvia Escayola and Prof. Miquel Solà members of the DiMoCat group of the Institute of Computational Chemistry and Catalysis of the University of Girona. The cover is the result of the artistic inspiration of Sílvia Escayola.

We paper is also highlighted by the editor in the Spotlights on Recent JACS Publications.

You can go to the JACS website to read the abstract and the full article “Too Persistent to Give Up: Aromaticity in Boron Clusters Survives Radical Structural Changes”.

Jordi Poater, Clara Viñas, Ines Bennour, Sílvia Escayola, Miquel Solà*, Francesc Teixidor*
J. Am. Chem. Soc. 2020, 1429396–9407.
DOI: https://doi.org/10.1021/jacs.0c02228

 

Aromaticity in Boron Clusters Survives Radical Structural Changes

Whereas the aromaticity of closo boranes is widely accepted, less is known about the aromaticity of nido boranes. This work carried out by Prof. Francesc Teixidor, Prof. Clara Viñas, and Dr. Ines Bennour of the Institute of Materials Science of Barcelona (ICMAB-CSIC), Prof. Jordi Poater at the University of Barcelona (previous DiMoCat member) and Sílvia Escayola and Prof. Miquel Solà members of the DiMoCat group of the Institute of Computational Chemistry and Catalysis of the University of Girona, experimentally shows that deboronation of m-C2B9H12 is a difficult task, whereas deboranation of o-C2B9H12 is quite easy. Moreover, it is widely known that o-C2B10H12 isomerizes to m-C2B10H12 upon heating at 400 ºC. These two facts indicate that m-C2B10H12 is more stable than o-C2B10H12. To find a reason for the different stability of these two isomers, authors have analyzed the thermodynamic stability and aromaticity of these closo carboranes and their nido counterparts. Results show that the higher thermodynamic stability of m-C2B10H12 is not related to aromaticity differences but to the location of the C atoms in the carborane structure. It is also demonstrated that the aromaticity observed in closo boranes and carboranes is also present in their nido counterparts and, consequently, authors conclude that aromaticity in boron clusters survives radical structural changes. Further, sandwich metallocenes (e.g. ferrocene) and sandwich metallacarboranes (e.g. [Co(C2B9H11)2]) have traditionally been considered similar. In this work, it is shown that they are not. Metallacarboranes display global aromaticity, whereas metallocenes present local aromaticity in the ligands. Remarkable and unique is the double probe given by 1H- and 11B-NMR tracing the reciprocally antipodal endocyclic open face Hec and B1. These magnetic studies have permitted to correlate both nuclei and relate them to a diatropic current in the plane at the middle of the nido-[C2B9H12]. This observation is the first and unique data that proves experimentally the existence of diatropic currents, thence aromaticity, in nido clusters and is comparable to the existence of diatropic currents in planar aromatic compounds.

 

 

Poater, J.; Viñas, C.; Bennour, I.; Escayola, S.; Solà*, M.; Teixidor*, F. Too Persistent to Give Up: Aromaticity in Boron Clusters Survives Radical Structural Changes. J. Am. Chem. Soc., 2020, DOI: 10.1021/jacs.0c02228

Financial support: This work has been supported by the Ministerio de Economía y Competitividad (MINECO) of Spain (Projects CTQ2017-85341-P, CTQ2016-77558-R, and MDM-2017-0767) and the Generalitat de Catalunya (projects 2017SGR39 and 2017SGR348). Excellent service by the Supercomputer center of the Consorci de Serveis Universitaris de Catalunya (CSUC) is gratefully acknowledged.