The formation of dimers via complexation was achieved but the ion intensity of the dimer in the mass spectrum was weak. These dimers have a significantly larger mass than the monomer, which reduces their detection efficiency in mass spectrometry. Additionally, because [BF4] -attached to the dimer with various combinations, the peaks originating from the dimer were observed across a range of m/z ratios. Furthermore, the addition of [BF4] -causes a widening of the isotope distribution, further decreasing the apparent intensity of the peaks. For example, in Fig. , peaks corresponding to the addition of 1-5 [BF4] -ions to the dimer were observed, resulting in charge states ranging from +3 to +7. These factors contribute to the apparent low yield of the dimer in the mass spectrum. However, from the data in Fig. ) and Fig. , we estimate that all 21 units included in the mixture with 24.4% molar ratio were likely forming dimers at the equivalence point of [Fe 2+ ]/[20-2] = 0.18.