New Cu(II)4 and Zn(II)4 complexes: Synthesis, characterization and magnetic and biological studies

Two new isomorphous tetranuclear complexes Cu₄L₂(4,4′-bipy)₂]·(ClO₄)₄·2CH₃CN·2H₂O (1) and Zn₄L₂(4,4′-bipy)₂]·(ClO₄)₃·CH₃O·4H₂O (2) have been obtained and fully characterized (where bipy = bipyridine, H₂L = macrocycle is the 2+2] condensation product of 2,6-diformyl-4-fluoro-phenol and 1,4-diaminobutane). They exhibit wheel-like configuration in which two 4,4′-bipy molecules connect two dinuclear M₂L]²⁺ units. The interactions of the complexes with calf thymus DNA were studied by UV-Vis and CD spectroscopic techniques. The binding constants of 1 and 2 are 2.27 × 10⁶ and 3.89 × 10⁵ M⁻¹, respectively. The magnetic measurement of 1 reveals that there are strong antiferromagnetic coupling (J = -272.6 cm⁻¹) between two Cu(II) ions in the macrocyclic unit and ferromagnetic interaction (j′ = 41.7) between the Cu(II) ions in two adjacent macrocyclic units. Furthermore, the cyclic voltammogram of 1 shows that it undergoes two quasi-reversible processes with the half wave potentials -0.232 and -0.606 V, respectively.