Fig. ) shows the ESI mass spectrum of the product obtained by adding H-PA and H-C2PhTpy to an acetonitrile solution of 1•(BF4 -)3 in the presence of a base (triethylamine). The mass spectrum mainly exhibited peaks attributed to 20 and 21. This result confirms that two Cl -ligands on the Au13 cluster surface were substituted by PA or C2PhTpy. When C2PhTpy were introduced more excessively, 22 forms and the subsequent addition of Fe 2+ could result in the formation of dimers or larger assemblies (Scheme S2A). Therefore, during the synthesis of the BB cluster, the molar ratio of acetylide ligands to H-PA:H-C2PhTpy was set to 0.9:0.1 to minimize the formation of 22, while achieving the desired formation of 21 (Fig