Characterization of CO in Rh{sub 6}(CO){sub 16}/NaY clusters and isolated Rh{sup +}(CO){sub 2}/NaY by solid-state {sup 13}C NMR Spectroscopy
Journal Article
·
· Journal of Physical Chemistry
- Ames Lab., IA (United States)
Solid-state NMR spectroscopy of {sup 13}C is used to structurally characterize and quantify carbonyl groups in Rh{sub 6}(CO){sub 16} and Rh{sup +}(CO){sub 2} complexes entrapped in NaY zeolite. MAS NMR line shape simulations show that the dicarbonyl groups present in Rh{sub 6}(CO){sub 16} and Rh{sup +}(CO){sub 2} have the same shielding parameters ({sigma}{sub iso} nearly equals 178 ppm, CSA nearly equals 400 ppm, and {eta} nearly equals 0.2) but exhibit greatly different spin-lattice relaxation rates. Bridged groups exist only in clusters and are bonded to three Rh atoms. Their shielding parameters [{sigma}{sub iso} nearly equals 251 ppm, CSA nearly equals 180 ppm, and negligible anisotropy ({eta})] differ from bulk Rh{sub 6}(CO){sub 16} and from those found earlier for CO bridged between two Rh atoms. The Rh{sub 6}:Rh{sup +} ratio can be measured directly from the MAS spectra or from the relaxation data. The residual broadening of 150-200 Hz in the MAS spectra is due to distribution of isotropic resonances in the sample. All CO species are immobile at room temperature on the NMR time scale (of the order of a millisecond), whereas slow exchange between dicarbonyls on hexarhodium clusters and isolated rhodium cations was found at 380 K. 21 refs., 2 figs., 2 tabs.
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 232533
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 14 Vol. 100; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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