AbstractThe work presented here describes the synthesis of new copper(II) complexes derived from 2‐amino‐5‐(pyridin‐2‐yl)‐1,3,4‐oxadiazole (L1) and 2‐methylamino‐5‐(pyridin‐2‐yl)‐1,3,4‐oxadiazole (L2) which also incorporate azido (N3–),thiocyanato (NCS–), cyanato (NCO–), dicyanamido [N(CN)2–, dca] and malonato (C3H2O42–, mal) coligands. Structures of the [Cu(L2)(mal)(H2O)]·2H2O (1), [{Cu(L2)(mal)}2] (2), [Cu(L2)2(NCS)2] (3), [Cu(L1)(NCS)2]n (4) and [{Cu(L2)}2(dca)2](ClO4)2·2H2O (5) compounds show the dependence of the dimensionality on parameters such as the type of oxadiazole and coligand utilised, solvents or reaction times. In this sense, 1 and 3 are mononuclear complexes, 2 contains centrosymmetric dinuclear entities, 4 is a 1D compound in which thiocyanato groups act as end‐to‐end bridges and 5 shows a 2D arrangement of dinuclear motifs linked through dicyanamido spacers. The copper(II) ions acquire distorted octahedral (3 and 4), square‐pyramidal (1 and 2) and trigonal bipyramidal (5) geometries. Stacking π–π interactions and hydrogen bonds stabilise the crystal frameworks. Water tetramers are present in 1. Spectroscopic (infrared, UV/Vis absorption and electron spin resonance) studies have also been developed for 1–5 and for the Cu(L2)(dca)2(H2O) (6), Cu(L2)(NCO)2 (7) and Cu(L2)2(N3)2(H2O)2 (8) complexes. The studies suggest the coordination of oxadiazole and coligands in all cases. Magnetic measurements show antiferromagnetic coupling for compound 5, ferromagnetic interactions for compound 2 and paramagnetic behaviour in compound 4. The susceptibility data were fitted by using the Bleaney–Bowers' equation for the copper(II) dimers derived from H = –2JS1S2. The resultant J/k values are +2.15 and –38.3 K for compounds 2 and 5, respectively. Magneto‐structural correlations are discussed and extended to more than 30 published dinuclear Cu(NN)2Cu′ diazole‐only bridged compounds. All these systems show J values close to or greater than those given by the expression J ≈ –90 + 3 Δβ (where Δβ is the difference between the Cu–N–N and Cu–N′–N′ angles). The artificial nuclease activity of 1, 2, 3 and 5 in the presence of mercaptopropionic acid or glutathione has also been analysed and compared with that exhibited by [Cu(L2)2(H2O)2](NO3)2 and CuSO4. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)