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

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)(H2O)(4)][S2O6](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)(H2O)(4)][S2O](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)(NO3)(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.