Fig. 1: Types of dimers.

a, b Two types of Cu²⁺ dimers on silica surfaces. c Cu²⁺ dimer in water. Yellow, red, blue, white, and green represent Si, O, O(water), H, and Cu atoms, respectively. Only silica atoms and the H₂O/OH⁻ O-atoms directly coordinated to Cu²⁺ are depicted as spheres; otherwise, they are lines or rods.