The best nuclease activities of 1,10-phenanthroline-copper complexes have been observed for a chelate/metal stoichiometry of 2/1. To favor this stoichiometry, the "Clip-Phen" ligand was synthesized with two 1,10-phenanthroline units linked via their C2-carbons by a short flexible arm. An exogenous amine function was present to allow future vectorization of this new chelating ligand. X-ray analysis of monocrystals of Clip-Phen confirmed its structure. An EPR study of (Clip-Phen)CuCl2 showed that the cupric ion was pentacoordinated with a water molecule as the possible fifth ligand. The Cu(I/II) redox couple was found to be near 85 mV vs SCE, close to the redox couple of (Phen)(2)CuCl2. A comparison of the nuclease activity of copper complexes of Clip-Phen and 1,10-phenanthroline indicated that (Clip-Phen)Cu was the more active.