Synthesis, crystal structure, magnetic property and oxidative DNA cleavage activity of an octanuclear copper(II) complex showing water-perchlorate helical network

A new octanuclear copper(II) complex has been synthesized and structurally characterized by X-ray crystallography: [Cu-8(HL)(4)(OH)(4)(H2O)(2)(ClO4)(2)].(ClO4)(2).2H(2)O (1) (H3L = 2,6-bis(hydroxyethyliminoethyl)-4-methyl phenol). The complex is formed by the linkage of two terminal bimetallic cationic units and a tetranuclear mu(3)-hydroxo bridged dicubane core by a very short intramolecular hydrogen bond (O-H center dot center dot center dot O, 1.48(3) angstrom and the angle 175 degrees). The coordination sphere of the terminal copper atoms is square pyramidal, the apical positions being occupied by water and a perchlorate ion. Complex 1 self-assembles to form a new type of water-perchlorate helical network [(H2O)(2)(ClO4)](infinity) involving oxygen atoms of coordinated perchlorate ion and the two lattice water molecules through hydrogen-bonding interaction. The variable temperature-dependent susceptibility measurement (2-300 K) of 1 reveals a strong antiferromagnetic coupling, J(1) = -220 cm(-1) and J(2) = -98 cm(-1) (J(1) and J(2) representing the exchange constant within [Cu2+](4) and [Cu2+](2) units, respectively). The complex binds to double-stranded supercoiled plasmid DNA giving a K-app value of 1.2 x 10(7) M-1 and displays efficient oxidative cleavage of supercoiled DNA in the presence of H,O, following a hydroxyl radical pathway. (c) 2006 Elsevier Inc. All rights reserved.