Room temperature O transfer from N2O to CO mediated by the nearest Cd(i) ions in MFI zeolite cavities

Abstract

The dominant oxidation state of cadmium is +II. Although extensive investigations into the +II oxidation state have been carried out, the chemistry of Cd^I is still largely underdeveloped. Here, we report a new functionality of cadmium created by the zeolite lattice: room temperature O transfer from N₂O to CO mediated by the nearest monovalent cadmium ions in MFI zeolite. Thermal activation of Cd^II ion-exchanged MFI zeolite in vacuo affords the diamagnetic [Cd^I–Cd^I]²⁺ species with a short Cd^I–Cd^I σ bond (2.67 Å). This species generates two Cd^I˙ sites under UV irradiation through homolytic cleavage of the Cd^I–Cd^I σ bond, and the thus-formed nearest Cd^I˙ sites abstract an O atom from N₂O to generate the [Cd^II–O_b–Cd^II]²⁺ core, where O_b means bridged oxygen. This bridging atomic oxygen species is transferred to CO at room temperature, through which CO oxidation and regeneration of the Cd^I–Cd^I σ bond then proceed. This is the first example pertaining to the reversible redox reactivity of the nearest monovalent cadmium ions toward stable small molecules. In situ spectroscopic characterization captured all the intermediates in the reaction processes, and these data allowed us to calibrate the density-functional-theory cluster calculations, by means of which we were able to show that the charge compensation requirement at the nearest two Al sites arrayed circumferentially in the 10-membered ring of MFI zeolite creates such novel functionalities of cadmium. The unprecedented reactivity of Cd^I and its origin are discussed.