Synthesis, structure, magnetism and nuclease activity of tetranuclear copper(II) phosphonates containing ancillary 2,2′-bipyridine or 1,10-phenanthroline ligands

The reaction of cyclohexylphosphonic acid (C6H11PO3H2), anhydrous CuCl2 and 2,2'-bipyridine (bpy) in the presence of triethylamine followed by a metathesis reaction with KNO3 afforded [Cu-4(mu-Cl)(2)(mu(3)-C6H11PO3)(2)(bpy)(4)](NO3)(2) (1). In an analogous reaction involving Cu(OAc)(2)center dot H2O, the complex [Cu-4(mu-CH3COO)(2)(mu(3)-C6H11PO3)(2)(2,2'-bpy)(4)](CH3COO)(2) (2) has been isolated. The three-component reaction involving Cu(NO3)(2)center dot 3H(2)O, cyclohexylphosphonic acid and 2,2'-bipyridine in the presence of triethylamine afforded the tetranuclear assembly [Cu-4(mu-OH)(mu(3)-C6H11PO3)(2)(2,2'-bpy)(4) (H2O)(2)](NO3)(3) (3). Replacing 2,2'-bipyridine with 1,10-phenanthroline (phen) in the above reaction resulted in [Cu-4(mu-OH)(mu(3)-C6H11PO3)(2)(phen)(4)(H2O)(2)](NO3)(3) (4). In all the copper(II) phosphonates (1-4) the two phosphonate ions bridge the four copper( II) ions in a capping coordination action. Each phosphonate ion bridges four copper(II) ions in a mu(4), eta(3) coordination mode or 4.211 of the Harris notation. Variable-temperature magnetic studies on 1-4 reveal that all four complexes exhibit moderately strong intramolecular antiferromagnetic coupling. The DNA cleavage activity of complexes 1-4 is also described. Compounds 1 and 3 were able to completely convert the supercoiled pBR322 DNA form I to nick form II without any co-oxidant. In contrast, 50% conversion occurred with 2 and 40% with 4. In the presence of magnesium monoperoxyphthalate all four compounds achieved rapid conversion of form I to form II.