The 13C CP-MAS NMR spectrum of [C6H16N2O]SbCl5 is shown in
Fig. 5. It exhibits six broad and asymmetric resonances corresponding to the six crystallographically independent carbon atoms as
revealed by X-ray structure determination. The observed asymmetry and broadening of the lines are caused by the 13C–121Sb
coupling.
Theoretical calculations were undertaken in order to assign the
NMR resonances to the different crystallographically independent
carbon atoms of the unit cell. The theoretical chemical shifts were
subtracted from those of the reference (tetramethylsilane) calculated at the same level of theory. The results, listed on Table 4,
show a very good agreement between theory and experiment.
It is worth noticing that the discrepancy between the calculated
and experimental values is mainly due to the fact that an isolated
molecule was taken into account. A better agreement should be
obtained by using periodic calculations but such studies are much
time consuming and could not be done on this system. However
such calculations allow to see where the effect of the surrounding
molecules is the most important and so can be correlated indirectly
to the X-ray data.