Binuclear copper(II) complexes with N4O3 coordinating heptadentate ligand: synthesis, structure, magnetic properties, density-functional theory study, and catecholase activity

The N4O3 coordinating heptadentate ligand afforded binuclear complex Cu 2(H 2L)(mu-OH)](ClO4)2 (1) and Cu2(L)(H2O)2]PF6 (2). In complex 1, two copper ions are held together by mu-phenoxo and mu-hydroxo bridges, whereas in complex 2, the copper centers are connected only by a mu-phenoxo bridge. In 1, both the Cu(II) centers have square pyramidal geometry (tau=0.01-0.205), whereas in the case of 2, one Cu(II) center has square pyramidal (tau=0.2517) and other one has square based pyramidal distorted trigonal bipyramidal (tau=0.54) geometry. Complexes 1 and 2 show an strong intramolecular and very weak antiferromagnetic interaction, respectively. Density-functional theory calculations were performed to establish the magneto structural correlation between the two paramagnetic copper(II) centers. Both of the complexes display a couple of one-electron reductive responses near -0.80 and -1.10 V. The complexes show significant catalytic activity at pH 8.5 on the oxidation of 3,5-di- tert-butylcatechol (3,5-DTBC) to 3,5-di- tert-butylquinone (3,5-DTBQ), and the activity measured in terms of kcat=29-37 h(-1).