Precise Identification of the Infrared Bands of the Polycarbonyl Complexes on Ni–MOR Zeolite by 12 C 16 O– 13 C 18 O Coadsorption and Computational Modeling

We report a combined computational and experimental IR study of polycarbonyl species on Ni–MOR zeolite formed after adsorption of 12C16O/13C18O isotopic mixtures, which allowed us to suggest a justified assignment of the vibrational bands in the complex IR spectra. For identification of all individual IR bands of the polycarbonyl complexes containing either the same or mixed isotopic probe molecules, we modeled the corresponding species with density functional method. In order to provide reliable computed values for comparison with experimentally measured vibrational frequencies of CO in the complexes, we combined periodic density functional calculations (with gradient corrected exchange-correlation functional) with isolated cluster calculations using hybrid functional. In this way, we confirm that the Ni+ cations in this zeolite material are able to form di- and tricarbonyl complexes and thus feature high coordinative unsaturation as suggested earlier.