Chromium and molybdenum carbonyls on NaX zeolite: 13C and 17O NMR

Abstract Chemical shift anisotropy powder patterns for 13 C and 17 O resonances from chromium and molybdenum subcarbonyls in NaX zeolites have been observed as a function of temperature. The surface subcarbonyls formed at 393 K have room temperature NMR powder patterns for both 13 C and 17 O nuclei which are narrower than expected for static carbonyls. The spectra are consistent with rapidly exchanging carbonyl ligands on a metal tricarbonyl with a C—metal—C angle of about 75°. Above 400 K, the resonances significantly narrow and indicate isotropic motion for the tricarbonyl complex. This isotropic motion has an activation energy of about 30 kJ mol −1.