The effect of any polydispersity should also apply to these PGSE NMR results. However, the ESI-MS results suggest that the polydispersity of the MAO-based anions, even in aged material (e.g. Figure ) is very narrow with Ɖ = 𝑀 ̅ 𝑤 /𝑀 ̅ 𝑛 = 1.009 to 1.019 (Electronic Supporting Information MAO.xlsx). This suggests that the 𝑀 ̅ 𝐷 values for both ion-pairs 1 and 2 should be larger but not much larger than those estimated by ESI-MS. Clearly this is not the case, so we discuss possible reasons for this discrepancy.