IR investigation of Fe(CO)5 adducts at the surface of silicalite, ZSM-5, zeolite-Y and g-Al2O3

The primary product of the room-temperature interaction of Fe(CO)5 with Lewis and Brønsted acid centers at the surfaces of ZSM-5, H-Y, and γ-Al2O3 is in all cases represented by O-bonded adducts. On the basis of a complete vibrational assignment of the IR spectrum of the surface adducts, it is concluded that Fe(CO)5 oxygen bonded to Lewis acid centers has approximate C3v symmetry. The frequencies of the O-bonded carbonyl are lowered by about 150-200 cm-1 (Al3+tet) and 100-150 cm-1 (Al3+oct) with respect to the unperturbed carbonyl molecule, while the other modes are raised by 40-50 and 25-40 cm-1, respectively. In Fe(CO)5 oxygen bonded (or hydrogen bonded) to Brønsted sites (H-Y zeolite), the perturbed carbonyl frequency is 50 cm-1 lower than that of the unperturbed carbonyl.