Copper complexes of a p-phenylenediamine-based bis(tridentate) ligand

Abstract

A new bis(tridentate) compound, N,N,N′,N′-tetrakis(2- pyridylmethyl)benzene-1,4-diamine (tpbd), its diprotonated derivative, [H ₂ tpbd] ²⁺ , and a dicopper complex [Cu ₂ (tpbd)(H ₂ O) ₄ ][S ₂ O ₆ ] ₂ have been prepared and structurally characterized. The pyridyl nitrogen atoms are strongly hydrogen bonded in the crystal structure of the yellow diprotonated salt tpbd·2HClO ₄ ·2Me ₂ CO. The bis(picolyl)amine ends of the ligand show a meridional-type co-ordination to the copper ions in the complex. Magnetic susceptibility measurements on [Cu ₂ (tpbd)(H ₂ O) ₄ ][S ₂ O] ₂ indicate that the p-phenylenediamine bridge commutes a weak antiferromagnetic coupling [J = -15.56(6) cm ^-1 ]. Two related dicopper complexes, Cu ₂ (tpbd)Cl ₄ and Cu ₂ (tpbd)(NO ₃ ) ₄ , were also isolated. The ESR spectra of the chloride and nitrate complexes indicated negligible magnetic exchange coupling. Reaction of tpbd with one-electron oxidants generated a purple radical cation which has been characterized by ESR and UV/VIS spectroscopy.