The crystal structures of two complexes containing the peroxodisulfate anion are reported, namely μ-peroxodisulfato-1κO:2κO′-bis[(acetato-κ²O,O′)aqua(2,2′:6′,2″-terpyridine-κ³N,N′,N″)cadmium(II)] heptahydrate, [Cd₂(C₂H₃O₂)₂(S₂O₈)(C₁₅H₁₁N₂)₂(H₂O)₂]·7H₂O, (I), and catena-poly[[[bis(2,2′-bipyridine-κ²N,N′)mercury(II)]-μ-peroxodisulfato-κ²O:O′] 0.4-hydrate], {[Hg(C₁₀H₈N₂)₂(S₂O₈)]·0.4H₂O}_n, (II). In both structures, the anion behaves as a bridge, linking neighbouring coordination polyhedra in two different ways, either tightly bound to the heptacoordinated Cd²⁺ cation forming neatly separated dimeric entities in (I) or across a shorter O–S–O path producing weakly connected chains by way of ‘semicoordination’ to the Hg²⁺ cations in (II).