The heterobifunctional ligand 5-[4-(1,2,4-triazol-4-yl)phen­yl]-1H-tetra­zole and its role in the construction of a Cd^II metal–organic chain structure

5-[4-(1,2,4-Triazol-4-yl)phen­yl]-1H-tetra­zole, C₉H₇N₇, (I), an asymmetric heterobifunctional organic ligand containing triazole (tr) and tetra­zole (tz) termini linked directly through a 1,4-phenyl­ene spacer, crystallizes in the polar space group Pc. The heterocyclic functions, serving as single hydrogen-bond donor (tz) or acceptor (tr) units, afford hydrogen-bonded zigzag chains with no crystallographic centre of inversion. In the structure of catena-poly[[di­aqua­cad­mium(II)]bis{μ₂-5-[4-(1,2,4-triazol-4-yl)phenyl]tetra­zol-1-ido-κ²N¹:N^1′}], [Cd(C₉H₆N₇)₂(H₂O)₂]_n, (II), the Cd^II dication resides on a centre of in­version in an octa­hedral {N₄O₂} environment. In the equatorial plane, the Cd^II polyhedron is built up from four N atoms of two kinds, namely of trans-coordinating tr and tz fragments [Cd—N = 2.2926 (17) and 2.3603 (18) Å], and the coordinating aqua ligands occupy the two apical sites. The metal centres are separated at a distance of 11.1006 (7) Å by means of the double-bridging tetra­zolate anion, L⁻, forming a chain structure. The water ligands and tz fragments inter­act with one another, like a double hydrogen-bond donor–acceptor synthon, leading to a hydrogen-bonded three-dimensional array.