Coordination Behaviors of Diphenylketene Adsorbed in the Nanocages of Zeolite NaY and AgY

We investigated in detail how polar cumulene molecules like diphenylketene were accommodated in faujasite zeolite pores based on 13C CP/MAS and DD/MAS NMR analyses as well as quantum chemical calculations after adsorbing the molecule into the zeolite NaY or AgY having “hard” sodium ions or “soft” silver ions. Since the diphenylketene has such a specific structure that a carbonyl group (a hard base) is accumulated by a carbon-carbon double bond (a soft π base), which is conjugated with two benzene rings (soft π bases), it is possible for the diphenylketene to adopt multicoordination modes to different metal ions in the zeolite. Compared with the coordination modes of benzophenone and 1,1-diphenylethene adsorbed in the NaY and AgY, those of diphenylketene were identified, and specific coordination behaviors in the zeolite’s supercages were classified depending on the hard or soft metal characters: The C=O and phenyl coordination modes to Na+ in NaY prevail, while the C=C and phenyl coordination to Ag+ in AgY is favored. We also unveiled the difference in the molecular mobility depending on the types of cations in the zeolite by comparing the 13C CP/MAS and DD/MAS NMR spectra.