To conclusively probe the assignment, experiments in neat pyridine-d5 were performed (no CD3OD was present in the sample). In this case both 1 and 2 are directly observable, with 2 being the dominant form (Figure )). However, 2 can be readily removed from solution by exchanging Cl -with PF6 -, leaving 1 as the only detectable species (Figure Therefore, we attribute the broad peak at -26.71 ppm in the CEST spectrum (Figure ) to the exchanging complex 3, [Ir(IMes)(Py)2(CD3OD)(H)2] + Cl -. In 3, one of the equatorial positions is occupied by the solvent molecule (CD3OD). As the peak is broad (FWHM ~4.5 ppm) and no doublet structure is observable, we conclude that 3 is in the intermediate exchange regime between two forms where the solvent occupies one of the two different equatorial positions in the complex. The strong line-broadening of this peak is most likely the reason why it was not detected in previous studies, showing the utility of CEST in detecting such species.