Synthesis, crystal structure, magnetic property and DNA cleavage activity of a new tereplithalate-bridged tetranuclear copper(II) complex

A new terephthalate-bridged tetranuclear copper(II) complex has been synthesized and structurally characterized by X-ray crystallography: [Cu4(L)2(tp)(dmf)2] (1) (H3L = 1,3-bis(salicylideneamino)propan-2-ol, tp = terephthalate and dmf = N,N’-dimethylformamide). The dinucleating pentadentate character of the ligand (H3L) and the desired pair-of-dimers arrangement, through the incorporation of the bridging terephthalate moiety, is clearly evident from the structure of 1. The copper atoms are coordinated in a slightly distorted square pyramidal arrangement within each dinucleating half of the complex and are bridged mono-atomically by the secondary alkoxo oxygen of the ligand and di-atomically by the terephthalate moiety. The apical position is occupied by the oxygen atom of the dmf. The structure of 1 reveals a short intramolecular Cu–Cu separation (ca. 3.1 Å), in combination with long intramolecular copper separations (ca. 11 Å). The variable temperature-dependent susceptibility measurement (2–300 K) of 1 reveals a dominant ferromagnetic coupling, 2J = 18.70 cm-1. Complex 1 binds to double-stranded CT (calf-thymus) DNA giving a Kapp value of 1.25 × 107 M-1 and displays efficient cleavage of supercoiled pUC19 DNA in the presence of H2O2 following a hydroxyl radical pathway.