The first dicopper(II) complex of a new bis(1,5,9-triazacyclododecane) ligand: synthesis, crystal structure and magnetic coupling of the complex

A new binucleating macrocylic polyamine ligand based on 1,5,9-triazacyclododecane ([12]aneN3), 2,6-bis(1,5,9-triazacyclododecan-9-ylmethyl) benzoate (L), has been synthesized from a selectively Boc protected [12]aneN3 precursor and 2,6-bis(bromomethyl) benzoate. L can form a stable binuclear complex with Cu(II) in aqueous solution and the complex has been characterized by X-ray crystallography. The intramolecular binuclear Cu(II) centers are bridged by a μ-carboxyl group on L and separated by 5.947 Å. Both of the Cu(II) centers are coordinated by three amine nitrogens of [12]aneN3 subunit and one oxygen of the carboxyl group, as well as one azide anion, and each Cu(II) center is in a distorted square-pyramid environment. To our knowledge, this is the first binuclear Cu(II) complex formed with a bis([12]aneN3) ligand. Variable temperature magnetic susceptibility studies indicate that there exists intramolecular antiferromagnetic coupling (−2J=71.4 cm−1) between the two unpaired electrons of the two Cu(II) ions in complex I.