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The radionuclides ²²⁵Ac³⁺ and ²¹³Bi³⁺ possess favorable physical properties for targeted alpha therapy (TAT), a therapeutic approach that leverages α radiation to treat cancers. A chelator that effectively binds and retains these radionuclides is required for this application. The development of ligands for this purpose, however, is challenging because the large ionic radii and charge-diffuse nature of these metal ions give rise to weaker metal–ligand interactions. In this study, we evaluated two 18-membered macrocyclic chelators, macrodipa and py-macrodipa, for their ability to complex ²²⁵Ac³⁺ and ²¹³Bi³⁺. Their coordination chemistry with Ac³⁺ was probed computationally and with Bi³⁺ experimentally via NMR spectroscopy and X-ray crystallography. Furthermore, radiolabeling studies were conducted, revealing the efficient incorporation of both ²²⁵Ac³⁺ and ²¹³Bi³⁺ by py-macrodipa that matches or …