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

We consider 29Si and 19F MAS NMR spectra of isolated 29Si(19F)2 and 29Si(19F)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 19F 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 29Si(19F)2 and 29Si(19F)3 spin systems and other dipolar coupled two and three-spin systems are discussed.