Formation of nonclassical carbonyls of Au3+ in zeolite NaY:: Characterization by infrared spectroscopy

Adsorption of CO on gold supported in zeolite NaY at 85 K led to the formation of (i) various carbonyls and isocarbonyls typical of the zeolite and (ii) carbonyls formed at cationic gold sites (observed in the 2186-2171 cm(-1) region). Analysis of the behavior of the bands allows their assignment to carbonyls of Au3+ ions. At temperatures higher than 220 K, CO adsorption led to the formation of a new type of Au3+-CO species (2207 cm(-1)). Once formed, these complexes could be transformed into the dicarbonyls Au3+ (CO)(2) when the sample was cooled to 85 K in the presence of CO. The results are explained by migration of Au3+ ions to more accessible positions within the zeolite at increasing temperatures. When a CO molecule is already adsorbed, it stabilizes the Au3+ ion in the new position, and a second CO molecule can be coordinated, thus forming a geminal species. These results are the first evidence of Au3+(CO)(2) complexes.