17o-esr evidence for zeolite matrix isolation of a square planar zno3 ring radical with c2v symmetry

Atomic-level insights into the geometric and electronic states of the metal-ozonide sequence remain scarce. We have recently found that a zeolite catalyst has a local environment to isolate the extremely rare mononuclear ZnII- ozonide species. In the present study, each atomic oxygen radical of the ZnII-ozonide species was selectively labeled with 17O, and each local environment was analyzed by electron spin resonance (ESR) spectroscopy at an X-band frequency, computer simulations of ESR spectra, density functional theory (DFT) calculations, and ab initio molecular dynamics (AIMD) simulations. The two types of 17O hyperfine structures assignable to the C2v geometry of a square planar ZnO3 ring radical were obtained experimentally. The DFT calculations ascertained the ground-state C2v geometry of the ZnII-ozonide adduct. This model provides 17O-hyperfine coupling constants that correspond well with the experimental parameters, supporting the generation of the C2v ZnO3 ring radical. The C2v ZnO3 ring radical is stable even at around room temperature, as evidenced by the similarity in the ESR spectra collected at 300 and 4 K. Such an unusual stability was supported by AIMD simulations, where C2v geometry was preserved at least for 50 ps at 300 K. Molecular orbital analyses showed that the ozonide species is stabilized via the highly polarized ZnII-(O3 - ) bonds. These interactions led to the polarization of two O-O bonds in the ozonide adduct, through which both side oxygens becomes anionic states, but the central oxygen becomes a cationic state. The zeolite lattice plays a pivotal role in constraining the effective charge of Zn close to (+2) and thereby stabilizing such a highly polarized ZnII-(O3 - ) bond. These novel findings suggest that the zeolite lattice has the potential as the ligand to create reactive metal-oxygen radicals with an unprecedented shape and ionic states.