How to Constrain Metal–Oxyl Bonds on a Solid Surface? Lesson from Isovalent Zn(II)–Oxyl and Ga(III)–Oxyl Bonds Isolated in Zeolite Matrix

Abstract

Isolation of the atomic O radical anion bound to a metal ion (metal–oxyl) on solid surfaces is highly desirable for an understanding of how we should design the surface structure for using oxyl as the reactive site. Owing to the analytical difficulty of oxyl, however, even identification of oxyl remains scarce. Herein, we report isovalent ZnII–oxyl and GaIII–oxyl bonds isolated in the zeolite matrix. Close similarities in reactivity, spectroscopic property, and bonding nature were observed between them, but their site requirements were entirely different; the former is generated at the monovalent ion-exchangeable site, whereas the latter at the divalent ion-exchangeable site. This study strongly suggests that tuning the polarization of the metal–oxygen bond using the charge-controlled lattice oxygens is a useful way to constrain surface metal–oxyl bonds.

17O-ESR Evidence for Zeolite Matrix Isolation of a Square Planar ZnO3 Ring Radical with C2v Symmetry

“…This is indicative that the electronic structure of the ZnO 3 ring radical is highly localized near the framework Al site, which is not inconsistent with the observation of the well-resolved vibrational fine structure (Figure ). , Similar cluster size independency was previously observed for the Co III –peroxo, Ni II –superoxo, Zn II –oxyl, − Ga III –ozonide, and Ga III –oxyl species isolated in the zeolite matrix, where a variety of vibronic progression features were observed even at RT. The effect of the Al position on the local geometry of the ZnO 3 core was also examined by periodic DFT calculations.…”

“…These novel findings suggest that the zeolite lattice has the potential as the ligand to create an unprecedented class of reactive metal–oxygen radicals and provide opportunities to analyze their states at an unprecedented level. Given the present result, as well as our previous reports, − ,,, we anticipate other cationic metal–ozonide bonds to be isolated and characterized in the future, which helps develop our understanding of the undeveloped chemistry of metal–ozonide.…”

“…Only a doublet spin state with a neutral charge was considered. Verifications of our computational conditions were previously verified …”

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

“…47−51 A breakthrough in an isolation approach for the stable metal ozonide species was reported in 2017 by Oda to actual practical conditions, not just cryogenic temperatures. 14,17,18,23 The first example of the stable single metal ozonide species is the [Zn II (O 3 −• )] + species that is stabilized as the counter cation for the negatively charged AlO 4 tetrahedra site. The [Zn II (O 3 −• )] + species was characterized by the vibronic progression rarely known in the heterogeneous catalyst.…”

“…18 Furthermore, even the divalent metal ozonide, that is, the gallium ozonide ring radical with a formula of [Ga III (O 3 −• )] 2+ , was able to be isolated by using divalent ion-exchange sites. 23 Thus, the isolation of reactive metal ozonide species, which has been difficult so far, is now possible on the reaction field of the functional material, the zeolite catalyst, and the chemistry of metal ozonide is undergoing a major development. The present paper newly reports the isolation of the single [Cd II (O 3 −• )] + species with the pseudo-C 2v symmetry.…”