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

Abstract

A new octanuclear copper(II) complex has been synthesized and structurally characterized by X-ray crystallography: [Cu 8(HL) 4(OH) 4(H 2O) 2(ClO 4) 2] · (ClO 4) 2 · 2H 2O ( 1) (H 3L = 2,6-bis(hydroxyethyliminoethyl)-4-methyl phenol). The complex is formed by the linkage of two terminal bimetallic cationic units and a tetranuclear μ 3-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 [(H 2O) 2(ClO 4)] ∞ 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 [Cu 2+] 4 and [Cu 2+] 2 units, respectively). The complex binds to double-stranded supercoiled plasmid DNA giving a K app value of 1.2 × 10 7 M −1 and displays efficient oxidative cleavage of supercoiled DNA in the presence of H 2O 2 following a hydroxyl radical pathway.