Two aqueous PuIV-desferrioxamine B (DFOB) complexes were characterized by one- and two-dimensional NMR techniques and an unexpected dimeric PuIVDFOB-di-μ-(O/OH)-PuIVDFOB complex was identified. Both “Curie” and “anti-Curie” behavior were observed for the dimeric species, yet the monomeric species only showed “anti-Curie” behavior. Diffusion ordered spectroscopy experiments showed an increase in particle size for the two species, which is indicative of a dimeric species. Bond lengths and coordination numbers estimated from X-ray absorption spectroscopy are consistent with the proposed structures.