A novel nuclear copper(II) complex is studied by variable temperature ESR spectra and susceptibility. The results show that at 300 K g ∥=2.06, g ⊥=2.12, g ∥< g ⊥ each copper(II) ion is in the environment of an almost regular trigonal bipyramidal geometry. In the range of 5~300 K with 2 J =0.5 cm -1 ,there is a weak ferromagnetic interaction between the two copper(II) ions.