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: [Cu8(HL)4(OH)4(H2O)2(ClO4)2] · (ClO4)2 · 2H2O (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 m3-hydroxo bridged dicubane core by a very short intramolecular hydrogen bond (O–H O, 1.48(3) Å and the angle 175°). 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)]¥ 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, J1 = -220 cm-1 and J2 = -98 cm-1 (J1 and J2 representing the exchange constant within [Cu2+]4 and [Cu2+]2 units, respectively). The complex binds to double-stranded supercoiled plasmid DNA giving a Kapp value of 1.2 × 107 M-1 and displays efficient oxidative cleavage of supercoiled DNA in the presence of H2O2 following a hydroxyl radical pathway.