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Diffuse reflectance FTIR spectroscopy was applied to the study of the fundamental C-O bond stretching vibrations and their first overtones and combination modes of copper carbonyl species formed upon CO adsorption on aqueous ion-exchanged CuZSM-5, CuM, CuY, and CuL zeolites autoreduced at 673 K in vacuo and on Cu(I)Y (sse) zeolite prepared by solid-state ion exchange of NH 4 Y with CuCl. At low CO pressures, different kinds of Cu(I)(CO) monocarbonyl species are formed depending upon the types of the zeolites. With increasing the CO pressure, Cu(I)(CO) 2 dicarbonyl species are formed on CuZSM-5, CuM, and CuY. After an evacuation of the preadsorbed CO at room temperature, the dicarbonyl species are transformed into monocarbonyl species. Such a transformation is reversible upon a change of the CO pressure. On the CuL zeolite, however, only one type of monocarbonyl is observed, no dicarbonyl species being detected even at high CO pressures. The frequency of the stretching vibration of the metal cation-carbon bond, i.e., Cu(I)-C bond, in the monocarbonyl species, which is difficult to detect directly by infrared measurements, can be calculated using the corresponding frequencies of the fundamental C-O bond stretching vibration and combination mode. It has been found that this frequency is much more sensitive to the electron donoracceptor ability of the Cu(I) cation in the monocarbonyl species than that of the fundamental C-O stretching vibration alone. On all of the zeolites except CuL, the monocarbonyl species characterized by the frequencies of fundamental C-O and Cu(I)-C bond stretching vibrations of 2157 and ∼440 cm -1 is observed. Another type of monocarbonyl species with its frequencies of fundamental C-O and Cu(I)-C bond stretching vibrations of about 2143 and 500 cm -1 is only formed on the high silica containing zeolites, CuZSM-5 and CuM. The Cu(I) cation in this type of monocarbonyl species possesses a very high electron donor-acceptor ability. On CuY, CuL, and CuZSM-5 (with a low copper loading) one more type of Cu(I) cations with a low electron donor-acceptor ability is detected by the CO probe. Those cations are able to form monocarbonyl species characterized by the lowest frequency of Cu(I)-C bond stretching vibration ranging within 390∼420 cm -1 .

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Diffuse reflectance FTIR spectroscopy has been applied to the study of fundamental C-0 bond stretching vibrations and their first overtones, and combination modes of copper(1) carbonyls, formed upon CO adsorption on CuNaY zeolite after reduction with CO at 400 "C. The frequencies of the combination modes of copper(1) carbonyls, e.g. fundamental C=O bond stretching vibrations plus M-C stretching or L MCO bending vibrations, were found to be much more sensitive to the composition and structure of Cu+-CO complexes than those of the fundamental stretching vibrations of C-0 bonds. Their analysis proved the formation of polycarbonylic species Cu+(CO),(x>,2) at room temperature and CO pressures of several kPa. These species, after removal of gaseous CO, were reversibly transformed into the thermally stable monocarbonyls. This finding prompted reconsideration of the literature data on the composition, structure and localisation of Cu+ carbonyls in Y zeolite. It was concluded that: (1) the reduction by CO of the Cu2+ ions to Cu+ proceeds without dealumination of the zeolite framework and creation of true Lewis acidic sites. (2) During adsorption of CO, Cu+ ions migrate from the sodalite cages into the supercages of the zeolite. (3) In the presence of gaseous CO the mean stoichiometry of Cu+ carbonyls differs from 1 CO molecule per 1 Cu+ cation. (4) A significant fraction of Cu+ ions is located in cationic positions, perhaps at S , , and S, sites, inaccessible to adsorbed CO molecules even at high CO pressures. (5) Cu+ forming carbonyls are located in the supercages, probably in s, , cationic positions.On leave from the N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Science, Moscow.

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