Chemically Induced Formation of Monovalent Cd+ Ions and Reversible O2 Activation in Cadmium-Loaded ZSM-5 Zeolite

We have studied the nature of monovalent Cd+ (4d10 5s1) species generated in a Cd-loaded HZSM-5 zeolite by reaction with molecular O2. The open-shell species formed in the different steps of the—reversible—reaction are characterized by electron paramagnetic resonance and hyperfine sublevel correlation (HYSCORE) spectroscopies at X- and Q-band frequencies. The same Cd+ species are obtained via a photochemical pathway through the UV irradiation of the Cd-loaded zeolite. Unambiguous evidence for the formation of mononuclear Cd+ species is obtained by the detection of the hyperfine interaction associated to the naturally abundant 111Cd and 113Cd magnetic isotopes (I = 1/2 natural abundance 12.8 and 12.22%, respectively). The full 111Cd A tensor (Ax = 10 620, Ay = 10 639, Az = 10 790 MHz) is resolved, indicating that 84% of the unpaired electron spin density is localized on the Cd ion. The small spin density delocalization on the zeolite framework is observed through the detection of 27Al hyperfine interactions by means of 6 pulse HYSCORE experiments, allowing for a detailed description of the geometric and electronic structure of the monovalent cadmium species and the zeolite stabilizing sites.