Fig. 2. Structural features involved in the metal-metal interactions of C-SACs.

(A) Bonding polarity of metal-metal interactions, reproduced with permission from Elsevier (42). (B) Bridging atoms between metal sites, reproduced with permissions from John Wiley and Sons (49). (C) Atomic arrangement of metal single atoms, reproduced with permission from the Nature Publishing Group (55). (D) Schematic illustration of topological structure of metal single atoms in Co₃O₄ matrix. From left to right: the crystal structure along <110> projection, corresponding projected tiling of Co₃O₄ (green, blue, and red refer to Co_oct, Co_tet, and oxygen), and topology illustration of crs (green) and dia (blue) nets with a polyhedron of metal single-atom sites (light green).