Rhodium Dicarbonyl Species on Silica and Alumina: Characterization with sup (13) C NMR.

A recent study proposed a method to determine quantitative site distributions for absorbed CO from broadline sup (13) C NMR spectra. The method involves the decomposition of the overlapping lineshapes based on proposed lineshapes for three individual components: linear- and bridge-bonded CO and Rh clusters and dicarbonyls on isolated Rh atoms. The spectra for a variety of samples could be fit by this model and the proposed lineshapes for the individual components were corroborated by isotropic shifts resolved in a magic-angle-spinning study and components isolated in relaxation studies. However, some inconsistencies suggested that the system was more complex. Specifically, the dicarbonyl species might constitute more of the spectra than first proposed.