The immobilization of open-shell transition metal complexes bearing unpaired electrons on carbon nanomaterials holds promise for a range of applications across spintronics, catalysis, and chemical sensing.^[1] Such hybrid systems combine the synthetic tunability of molecular complexes with the favorable optoelectronic properties of carbon-based nanostructures. However, existing approaches often disrupt either the structural integrity of the complex or the desirable properties of the carbon material. This challenge is exacerbated for complexes containing unpaired electrons, whose extreme sensitivity to ambient conditions typically limits their practical use.^[2-4] New approaches are therefore needed to both identify open-shell metal complexes exhibiting environmental stability and efficiently heterogenize them on carbon nanomaterials.

Herein, we present the non-covalent functionalization of carbon nanotubes with open-shell transition metal complexes.^[5] The complexes feature primarily ligand-centered radicals and are air- and moisture-stable, allowing for spectroscopic and electrochemical characterization under ambient conditions. Comprehensive solid-state characterization confirmed the structural integrity of the complex in the composite, with no disruption to the carbon nanotube framework and retention of its favorable optoelectronic properties. Electrochemical studies established that the material maintains stability over prolonged redox cycling, reversibly accessing three distinct redox states. This property was leveraged in preliminary electrochemical sensing studies of cyanide anions.^[6] Taken together, these results establish a modular sensing platform integrating environmentally stable open-shell complexes and conductive carbon supports.

[1] S.-X. L. Luo, T. M. Swager, Nat. Rev. Methods Primers 2023, 3, 73.

[2] M. Urdampilleta, S. Klyatskaya, J.-P. Cleuziou, M. Ruben, W. Wernsdorfer, Nat. Mater. 2011, 10, 502–506.

[3] S. Ncube, C. Coleman, A. Strydom, E. Flahaut, A. de Sousa, S. Bhattacharyya, Sci. Rep. 2018, 8, 8057.

[4] M. J. Bezdek, S.-X. L. Luo, K. H. Ku, T. M. Swager, Proc. Natl. Acad. Sci. USA 2021, 118, e2022515118.

[5] S. L. Kleynemeyer, A. M. Wu, Y. Pan, F. Krumeich, M. J. Bezdek, Manuscript in preparation.

[6] J. Ma, P. K. Dasgupta, Anal. Chim. Acta 2010, 673, 117–125.