Polynuclear complexes of a new macrocyclic oxamide metalloligand: Syntheses, crystal structures and deoxyribonucleic acid cleavage and magnetic properties

A mononuclear macrocyclic oxamide complex CuL was used as a new metalloligand to prepare polynuclear complexes, by which a new tetranuclear complex {Mn[CuL(ClO4)]3}·H3O·2.5H2O (1) and a new trinuclear complex {Cu[CuL(CH3OH)]2(ClO4)2} (2) were obtained (H2 L = dimethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo-[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate). X-ray single crystal analysis revealed that every Cu(II) centre of the CuL metalloligand is coordinated by the four N atoms from the macrocyclic oxamide ligand and an O atom from a ClO4− anion in 1 or a CH3OH molecule in 2, with the four N atoms forming the square base and the O atom occupying the vertex of the distorted square pyramidal coordination geometry. Plasmid DNA cleavage experiments showed that complexes CuL, 1 and 2 all have cleavage activities in the absence of any added oxidizing agents and that 2 has the highest cleavage efficiency among the three complexes in Tris–HCl buffer. Synergistic effects between the Cu(II) centers may contribute to the higher DNA cleavage efficiency of 2 in Tris–HCl buffer. Magnetism studies over the temperature range 2–300 K showed pronounced antiferromagnetic interactions between the oxamido-bridged metal centers in both 1 and 2.