A more precise extraction of the quadrupolar parameters from the experimental data was achieved through the simultaneous fitting of the spectra acquired at 14.1 and 21.15 T using a routine which treats the quadrupolar interaction in an exact fashion (for details on data analysis see SI). In principle, CSA parameters (i.e. the span and the skew, as well as the Euler angles relating CSA and EFG principal axes frames) could be extracted simultaneously. However, the resulting increase in the number of fitting parameters precludes meaningful fitting of both, EFG and CSA values. To determine the optimal routine for extraction of EFG parameters, three separate fitting approaches were compared for 1-py and 1-TPPO. In addition to the simultaneous fitting of all EFG and CSA parameters, CQ, η and δiso