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 groupPc. 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 ofcatena-poly[[diaquacadmium(II)]bis{μ2-5-[4-(1,2,4-triazol-4-yl)phenyl]tetrazol-1-ido-κ2N1:N1′}], [Cd(C9H6N7)2(H2O)2]n, (II), the CdIIdication resides on a centre of inversion in an octahedral {N4O2} environment. In the equatorial plane, the CdIIpolyhedron is built up from four N atoms of two kinds, namely oftrans-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.