Formation of Ca2+(CO)(3) complexes during low-temperature CO adsorption onCaNaY zeolite

Adsorption of CO on CaNaY at 85 K results in formation of three types of ca lcium carbonyl complexes. At high CO coverage (equilibrium CO pressures abo ve ca. 100 Pa) Ca2+(CO)(3) species, characterized by an IR band at 2185 cm( -1), are predominant. These species are decarbonylated stepwise and first c onverted into Ca2+(CO)(2) dicarbonyls at decreasing coverage during evacuat ion. The latter complexes lose one CO ligand at further evacuation and form linear Ca2+-CO species that are quite stable at 85 K. Adsorption of a (CO) -C-12-(CO)-C-13 mixture reveals that the CO ligands in the di- and tricarbo nyls behave as independent oscillators. The results obtained are explained by the existence of three coordinative vacancies of Ca2+ cations in SU posi tions in Y zeolites.