(1,3,4‐Oxadiazole)copper(II) Compounds: Dimensionality, Magnetism and Nuclease Activity

The work presented here describes the synthesis of new copper(II) complexes derived from 2‐amino‐5‐(pyridin‐2‐yl)‐1,3,4‐oxadiazole (L 1 ) and 2‐methylamino‐5‐(pyridin‐2‐yl)‐1,3,4‐oxadiazole (L 2 ) which also incorporate azido (N 3 – ),thiocyanato (NCS – ), cyanato (NCO – ), dicyanamido [N(CN) 2 – , dca] and malonato (C 3 H 2 O 4 2– , mal) coligands. Structures of the [Cu(L 2 )(mal)(H 2 O)] · 2H 2 O ( 1 ), [{Cu(L 2 )(mal)} 2 ] ( 2 ), [Cu(L 2 ) 2 (NCS) 2 ] ( 3 ), [Cu(L 1 )(NCS) 2 ] n ( 4 ) and [{Cu(L 2 )} 2 (dca) 2 ](ClO 4 ) 2 · 2H 2 O ( 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(L 2 )(dca) 2 (H 2 O) ( 6 ), Cu(L 2 )(NCO) 2 ( 7 ) and Cu(L 2 ) 2 (N 3 ) 2 (H 2 O) 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 = –2 JS 1 S 2 . 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) 2 Cu′ diazole‐only bridged compounds. All these systems show J values close to or greater than those given by the expression J ≈ –90 + 3 Δ β (where Δ β 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(L 2 ) 2 (H 2 O) 2 ](NO 3 ) 2 and CuSO 4 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)