Freire-García, AntíaAlvarado de la Torre, Raúl ManuelCosta-DeDios, MaríaEsteban-Gómez, DavidPlatas-Iglesias, Carlos2026-04-082026-04-082026-02-24Freire-García, A.; Alvarado, R.; Costa-DeDios, M.; Esteban-Gómez, D.; Platas-Iglesias, C. Stabilities of Ac3+ Complexes Relevant as Radiopharmaceuticals. Inorg. Chem. 2026, 65 (9), 5119–5130. https://doi.org/10.1021/acs.inorgchem.5c05846.0020-16691520-510Xhttps://hdl.handle.net/2183/47895[Abstract] We present a detailed density functional theory (DFT) investigation of the structural features and thermodynamic stabilities of La3+ and Ac3+ complexes relevant to develop radiopharmaceutical agents. A total of 16 chelators were considered, covering the acyclic and macrocyclic families functionalized with different numbers and types of donor atoms. The bond distances of the Ac3+ coordination environment are systematically longer than those obtained for the La3+ analogues, which allowed us to estimate an ionic radius for Ac3+ in coordination number 9 of 1.275 ± 0.020 Å (1.216 and 1.206 Å were proposed for La3+). Energy decomposition analysis (EDA) provided hints into the nature of the metal–ligand interactions and their relative weight in La3+ and Ac3+ complexes. A thermodynamic DFT study allowed us to estimate the stability constants of the Ac3+ complexes from those of the La3+ ones, as for the latter experimental values are available in the literature. These studies evidenced that Ac3+ tends to form complexes with lower thermodynamic stability in comparison with La3+, with the exception of one of the leading chelators for Ac3+, MACROPA2–, and the unexpected case of OCTAPA4–. Overall, the methodology reported here will allow identifying chelators well suited for Ac3+ coordination, thereby aiding the design of radiopharmaceuticals based on [225Ac]Ac3+ for targeted α therapy (TAT).engAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/journal articleopen access10.1021/acs.inorgchem.5c05846