Sophisticated architectures assembled from a single class of subunits by cooperative interactions are ubiquitous in nature. The construction of their artificial mimics, however, remains one of the most formidable challenges facing synthetic chemists. Here, we report a hierarchical diamondoid superstructure—namely, a supramolecular diamond—that is constructed from the multiple-level self-assembly of a highly symmetrical salt, hexakis[(4,4′-bipyridin-1-ium)methylene]benzene hexafluorophosphate. The uniform octahedral single crystals, with 96 cationic organic fragments and 96 counteranions in a unit cell, can be prepared quantitatively in a controllable one-step procedure within seconds at ambient conditions. The sizes of the resulting samples are modulated from 280 nm to 660 μm. The mechanism of the self-assembly was elucidated at the atomic level. As proof of its intrinsically cationic superstructure with mobile anions, the three-dimensional nanoporous framework can exchange efficiently with metal oxoanions. This research shows that precisely tunable hierarchical assemblies can translate charged molecules into complicated architectures.