2,2′-{1,1′-[2,2′-Oxalylbis(hydrazin-2-yl-1-yl­idene)]diethyl­idyne}dipyridinium bis­(perchlorate) dihydrate

The title salt, C(16)H(18)N(6)O(2) (2+)·2ClO(4) (−)·2H(2)O, was obtained unintentionally as a major product in the reaction of Zn(ClO(4))(2)·6H(2)O with the N′,N′(2)-bis­[(1E)-1-(2-pyrid­yl)ethyl­idene]ethanedihydrazide (H(2) L) ligand. The (H(4) L)(2+) cation lies across a centre of inversion. The pyridiniumimine fragments of (H(4) L)(2+) adopt syn orientations. Intra­molecular N—H⋯N and N—H⋯O hydrogen bonds lead to the formation of S(5) motifs. In the crystal, neighbouring cations are connected by π–π inter­actions between pyridinium units with a centroid–centroid distance of 3.600 (1) Å. Moreover, the crystal components are assembled into two-dimensional layers via N—H⋯O and O—H⋯O hydrogen bonds, with no direct hydrogen-bonding inter­actions between cations.