Success in making Zn⁺ from atomic Zn⁰ encapsulated in an MFI-Type zeolite with UV light irradiation

For the first time, the paramagnetic Zn⁺ species was prepared successfully by the excitation with ultraviolet light in the region ascribed to the absorption band resulting from the 4s-4p transition of an atomic Zn ⁰ species encapsulated in an MFI-type zeolite. The formed species gives a specific electron spin resonance band at g = 1.998 and also peculiar absorption bands around 38,000 and 32,500 cm^-1 which originate from 4s-4p transitions due to the Zn⁺ species with paramagnetic nature that is formed in MFI. The transformation process (Zn⁰ → Zn ⁺) was explained by considering the mechanism via the excited triplet state (³P) caused by the intersystem crossing from the excited singlet state (¹P) produced through the excitation of the 4s-4p transition of an atomic Zn⁰ species grafted in MFI by UV light. The transformation process was well reproduced with the aid of a density functional theory calculation. The thus-formed Zn⁺ species which has the doublet spin state exhibits characteristic reaction nature at room temperature for an O₂ molecule having a triplet spin state in the ground state, forming an η¹ type of Zn²⁺-O₂^- species. These features clearly indicate the peculiar reactivity of Zn⁺ in MFI, whereas Zn⁰-(H⁺)₂MFI hardly reacts with O₂ at room temperature. The bonding nature of [Zn²⁺-O ₂^-] species was also evidenced by ESR measurements and was also discussed on the basis of the results obtained through DFT calculations.