(1,3,4-Oxadiazole)copper(II) compounds: Dimensionality, magnetism and nuclease activity

Abstract

The 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 (C3H2O4 2-, mal) coligands. Structures of the [Cu(L2)(mal)(H2O)]·2H 2O(1), [{Cu(L2)(mal)}2] (2), [Cu(L 2)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(H 2O)2](NO3)2 and CuSO4. © Wiley-VCH Verlag GmbH & Co. KGaA, 2009.