An excellent test of these ideas is comparison with results for the more weakly pairing anion BAr F- 4 . Using the slope from ε" vs. the concentration of Ir[tBu]-BAr F 4 (figure (b)), equation ( ), and a θ unpaired of 68.3 ps (calculated assuming loose ion pair association); we found the ground-state dipole moments of Ir[tBu]-BAr F 4 to be 4.82 D, consistent with our expectations for the range of possible dipole moment of Ir[tBu] + . If we assume contact-ion pairing on the other hand, we obtain a much larger dipolar relaxation time of θ paired = 367 ps due to the large size of the BAr F- 4 anion. Using this value we calculate a dipole moment of 10.8 D, which in this case is far too small to be consistent with the large intermolecular dipole moment expected for a contact-ion pair of Ir[tBu]-BAr F 4 , even when the anti-parallel vector sum of the intramolecular and intermolecular dipole moments and similar charge displacements are considered. This, combined with the consistency of the unpaired dipole we measure here with that of Ir(ppy) 3 (see Supplementary Fig. ), leads us to conclude that contact-ion pairs are absent for Ir[tBu]-BAr F 4 . Thus, our data is consistent with the idea that a majority of Ir[tBu]-PF 6 species in 1,4-dioxane form contact-ion pairs that self-organize to minimize the overall dipole moment, while the majority of Ir[tBu]-BAr F- 4 species exist as either solvent-separated ion pairs or dissociated ions, even in 1,4-dioxane.