doi:10.1038/s41467-026-69257-8engTarifa, LuisCano-Asensio, JuditLópez, José A.Tejel, CristinaGeer, Ana M.Cooperative anion activation at a cobalt center through ion pairing and ligand designART-2026-148717Weakly coordinating anions (WCAs) are commonly used to stabilize highvalent, electrophilic transition-metal complexes, owing to their low nucleophilicity and minimal coordinating ability. Here, we present a cobalt platform supported by a tris(2-pyridyl)(N-picolyl)imidazolidine ligand (Py4Im) that generates a directional, protic cavity for ion pairing. This environment enables a comparative study of BF4 – and PF6⁻, showing that PF6⁻ undergoes fluoride abstraction under mild conditions, while BF4 – remains unreactive unless assisted by a Lewis base. The PF6⁻ activation yields a well-defined CoIII–F complex that acts as an efficient nucleophilic fluoride source. DFT calculations and diffusion NMR experiments highlight the critical role of anion-cation pairing in modulating reactivity, overriding intrinsic thermodynamic preferences. These findings showcase supramolecular control of WCA activation by a late transition metal and provide new design principles for reactivity modulation via counterion selection.2026http://zaguan.unizar.es/record/17023410.1038/s41467-026-69257-8http://zaguan.unizar.es/record/170234oai:zaguan.unizar.es:170234info:eu-repo/grantAgreement/ES/AEI/PID2020-119512GB-I00info:eu-repo/grantAgreement/ES/AEI/PID2023-148472NB-I00info:eu-repo/grantAgreement/ES/DGA/E50-23Rinfo:eu-repo/grantAgreement/ES/MCIN/RYC2021- 033807-Iinfo:eu-repo/grantAgreement/ES/MICINN/RED2022-134074-TNature communications 17, 1 (2026), 2469 [11 pp.]by-nc-ndhttps://creativecommons.org/licenses/by-nc-nd/4.0/deed.esinfo:eu-repo/semantics/openAccess