Synthesis, Isolation, and Study of a Heterobimetallic Uranyl Crown-Ether Complex

Although crown ethers can selectively bind many metal cations, little is known regarding the properties of crown ether complexes of the uranyl dication, UO22+. Here, the synthesis and characterization of an isolable complex in which the uranyl dication is bound in an 18-crown-6-like moiety are reported. A tailored macrocyclic complex featuring an accessory Pt(II) center was used to drive capture of UO22+ by the crown, as demonstrated by results from single-crystal X-ray diffraction analysis. The U(V) oxidation state becomes accessible at a quite positive potential (E1/2) of –0.18 V vs. Fc+/0 upon complexation, representing the most positive UVI/UV potential yet reported for the UO2n+ core moiety. Joint computational studies show that the electronic structure of the U(V) form results in significant weakening of U–Ooxo bonding despite the quite positive reduction potential at which this species can be accessed, underscoring that crown-ligated uranyl species could demonstrate unique reactivity under only modestly reducing conditions.