Although we couldn't provide any quantitative measurement for the observed 𝐵𝐵𝐵𝐵 𝑀𝑀𝑀𝑀𝑀𝑀 + trend, from the NCI plot shown in Figure and S2, qualitatively it can be argued that the strong non-covalent interaction (NCI) present between the PF6 -anions and MMI + cations (shown in the green iso-surface) is responsible for the observed 𝐵𝐵𝐵𝐵 𝑀𝑀𝑀𝑀𝑀𝑀 + values for MMI + addition.