29Si and 19F MAS NMR spectra of isolated 29Si(19F)2 and 29Si(19F)3 spin systems:: experiments and simulations

We consider Si-29 and F-19 MAS NMR spectra of isolated Si-29(F-19)(2) and Si-29(F-19)(3) spin systems in two organosilicon compounds of the type RR'SiF2 and RSiF3 (R, R' = organic ligands). Experimental spectra are analysed by means of numerical simulations. It is found that the SiF3 group in RSiF3 is reorienting rapidly around the molecular Si-C bond direction in the solid state. The two F-19 shielding tensors in RR'SiF2 have strongly differing orientations relative to the two Si-F bond directions in the molecule. Possibilities and limitations of straightforward MAS NMR approaches for the full characterisation of Si-29(F-19)2 and Si-21(F-19)(3) spin systems and other dipolar coupled two and three-spin systems are discussed. (C) 2003 Elsevier Science (USA). All rights reserved.