Vegliante, AlessioVilas Varela, ManuelGómez Rodrigo, LucíaPeña Gil, Diego2025-09-162025-09-162025-05-30Alessio Vegliante, Manuel Vilas-Varela, Ricardo Ortiz, Francisco Romero Lara, Manish Kumar, Lucía Gómez-Rodrigo, Stefano Trivini, Fabian Schulz, Diego Soler-Polo, Hassan Ahmoum, Emilio Artacho, Thomas Frederiksen, Pavel Jelínek, Jose Ignacio Pascual, and Diego Peña (2025). On-Surface Synthesis of a Ferromagnetic Molecular Spin Trimer. Journal of the American Chemical Society, 147 (23), 19530-19538 DOI: 10.1021/jacs.4c157360002-7863https://hdl.handle.net/10347/42825Triangulenes are prototypical examples of openshell nanographenes. Their magnetic properties, arising from the presence of unpaired π electrons, can be extensively tuned by modifying their size and shape or by introducing heteroatoms. Different triangulene derivatives have been designed and synthesized in recent years thanks to the development of onsurface synthesis strategies. Triangulene-based nanostructures with polyradical character, hosting several interacting spin units, can be challenging to fabricate but are particularly interesting for potential applications in carbon-based spintronics. Here, we combine pristine and N-doped triangulenes into a more complex nanographene, TTAT, predicted to possess three unpaired π electrons delocalized along the zigzag periphery. We generate the molecule on a Au(111) surface and detect direct fingerprints of multiradical coupling and high-spin state using scanning tunneling microscopy and spectroscopy. With the support of theoretical calculations, we show that its three radical units are localized at distinct parts of the molecule and couple via symmetric ferromagnetic interactions, which result in a S = 3/2 ground state, thus demonstrating the realization of a molecular ferromagnetic Heisenberg spin trimer.eng© 2025 The Authors. Published by American Chemical Society. This article is licensed under CC-BY 4.0Attribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/Magnetic propertiesMoleculesQuantum mechanicsResonance structuresScanning tunneling microscopyjournal article10.1021/jacs.4c15736open access