To assess the generality of this two-step crystallization process, we conducted crystallization experiments varying the size ratio (β) between positive and negative particles. As shown in Extended Data Figure , we observed no substantial differences in the crystallization mechanism, although the resulting crystal structures varied as expected. Specifically, we examined systems with β = 0.36, 0.43, 0.50, 0.74, and 0.81, leading to the formation of Cs 6 C 60 -, NaCl-, K 4 C 60 -, Th 3 P 4 -, and CsCl-like structures, respectively.