Diaqua­bis[4‐(4H‐1,2,4‐triazol‐4‐yl)­benzoato‐κ2O,O′]cobalt(II), and the cadmium(II) and copper(II) analogues: new self‐complementary hydrogen‐bond donor/acceptor modules for designing hydrogen‐bonded frameworks

In the isostructural title complexes, [M(C₉H₆N₃O₂)₂(H₂O)₂] [M = Co^II, (I), Cd^II, (II), and Cu^II, (III); the metal centres reside on a twofold axis in the space group C2/c for (I) and (II)], the metal centres are surrounded by four O atoms from two O,O′‐bidentate carboxyl­ate groups and by two trans‐coordinated aqua ligands, forming a distorted octa­hedral environment. The mol­ecules possess four hydrogen‐bond donor (two aqua ligands) and four hydrogen‐bond acceptor sites (two triazole groups), and aggregate by self‐association, forming two‐dimensional hydrogen‐bonded frameworks [via O—H⋯N inter­actions; O⋯N = 2.749 (3)–2.872 (3) Å]. The layers are parallel and are tightly packed with short inter­layer distances of 4.93, 4.95 and 5.01 Å for (I), (II) and (III), respectively.