Actinium-225 is a promising isotope for targeted alpha therapy. Unfortunately, progress in developing chelators for medicinal applications has been hindered by a limited understanding of actinium chemistry. This knowledge gap is primarily associated with handling actinium, as it is highly radioactive and in short supply. Hence, Ac<sup>III</sup> reactivity is often inferred from the lanthanides and minor actinides (i.e. Am, Cm), with limited success. Recent upgrades and technological improvements at synchrotron facilities have provided new opportunities to overcome challenges associated with characterizing the coordination chemistry of actinium. Herein, we will present application of these new spectroscopic capabilities to conduct the first actinium X-ray absorption fine structure (XAFS) studies. Results will be compared with analogous measurements made on actinides in the +3 oxidation state. Spectra interpretations, guided by molecular dynamics-density functional theory (MD-DFT) calculations, will also be discussed. These results imply diverse reactivity for the +3 actinides and highlight the unexpected and unique Ac<sup>III</sup> chemical behavior.

X-ray absorption spectroscopy of actinium and comparison with actinide +3

254th National Meeting (2017)

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