Synthesis,crystal structure,magnetic property and DNA cleavage activity of a new terephthalate-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 K_app 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.