As can be seen from Tables S5-S8, bond lengths, angles and dihedrals of the conformers calculated using the ω97X-D level of theory are in good agreement among the various basis sets and the ω97X-D/6-311++(3df,2p) level of theory and basis set, and gives calculated results that best agree with those in the crystals . On the other hand, bond lengths calculated using the B3LYP level of theory show some variations larger than those in the crystals1 as well as ω97X-D. The energy of the planar-cis [EMI] + conformer relative to that of the non-planar staggered [EMI] + conformer calculated using the ω97X-D/6-311++(3df,2p) levels of theory and basis set and in the presence of dielectric continuum medium is 9.8 kJ mol -1 . According to the ω97X-D/6-311++(3df,2p) levels of theory and basis set and in the presence of dielectric continuum medium, the dipole moment of the non-planar staggered [EMI] + (µ =2.0550) conformer is slightly larger than that of the planar-cis [EMI] + one (µ = 1.3131), implying that the non-planar staggered [EMI] + geometry is preferred around more small sized anions.