Identification of a Stable Ozonide Ion Bound to a Single Cadmium Site within the Zeolite Cavity

Molecular metal oxides are invoked as the key intermediate in a variety of oxidative reactions. Although an atomic oxygen ligand and molecular O₂ ligands are well known, the triatomic oxygen ligand (ozonide) is very limited due to its instability. Here, we report a successful preparation and characterization of stable cadmium ozonide species. Our approach used the negatively charged local environments within the zeolite pore, which allowed us to isolate the single cadmium ozonide species as the counter cation even at room temperature. Its state was characterized by vibronic progressions closely similar to those observed in the cryogenic inert-element matrix system. Density functional theory calculations determined the lowest-energy geometry as the side-on [Cd^II(O₃^–•)]⁺ having C_2v symmetry. This model was stable within the ab initio molecular dynamics simulation at 300 K, rationalizing the abnormal stability of [Cd^II(O₃^–•)]⁺observed experimentally. The O₃-a₁ → Cd-5s-donation orbital interaction was the driving force for the formation of the stable Cd^II–(O₃^–•) bond. The zeolite lattice plays a pivotal role in the enhancement of the acidity of the cadmium ion and stabilizes the donation interaction but constrains the O₃ adduct as a pseudo-free ozonide ion. The findings in the present work will be applicable for designing new metal ozonide compounds.