We report the carbon-13 magic-angle-spinning nuclear magnetic resonance (NMR) spectra of silica-supported Os 3 ( 13 CO) 12 samples prepared in several different ways. Our results yield both the isotropic chemical shift and the principal components of the chemical shift tensor for each carbonyl resonance. Spectra have been assigned by comparison to solution NMR spectra of a variety of osmium carbonyl clusters that are models for the proposed surface-attached structures: HOs 3 (CO) 10 (OR) (R = CH 3 , C 6 H 5 , SiEt 3 ), HOs 3 (CO) 10 (O 2 CH), Os 3 (CO) 10 (OCH 3 ) 2 , and [Os(CO) 3 Cl 2 ] 2 . Spectra of samples prepared by impregnation of silica with a solution of Os 3 ( 13 CO) 12 provide evidence for a physisorbed Os 3 (CO) 12 species undergoing fast isotropic motion. For samples prepared by refluxing Os 3 ( 13 CO) 12 and SiO 2 in n-octane, a spectrum containing five distinct resonances is observed, consistent with a HOs 3 (CO) 10 (OSi=) species having C s symmetry. The chemical shift anisotropy parameters measured for these resonances at 20 °C suggest that this species is undergoing rapid (≫32 kHz) large-angle (90-120°) rotational jumps. Spectra of samples prepared by vacuum pyrolysis (200 °C) are consistent with Os(II) carbonyl species that are immobile on the 10 −5 -10 −4 -s time scale. These results demonstrate the utility of 13 C NMR spectroscopy for studying the structures and dynamics of supported metal carbonyl clusters.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry