Cu(Ⅰ) and Cu (Ⅱ) helical complexes formed with oligobipyridine ligand

A new asymmetric oligobipyridine ligand, 1-(5'-methyl-2, 2'-bipyridin-5-yl)-2-(6'-methyl-2, 2'-bipyridin-6-yl)ethane (L), in which the bipyridine units are bridged by CH_2CH_2 at 5, 6'-position has been synthesized. The ligand L reacts with Cu(Ⅰ) and Cu(Ⅱ) ions giving double-stranded helical complexes [Cu_2~ⅠL_2] (ClO_4)_2·Et_2O (1) and [Cu_2~ⅡL_2 (OH) (H_2O)][ClO_4]_3(2), respectively. Complexes 1 and 2 were characterized by X-ray diffraction analyses, ES-MS, ESR and cyclic voltammetry, etc. Differing from the oligobipyridine ligands bridged by CH_2CH_2 at 6,6'-or 5,5'-position, the ligand L not only forms a double-stranded helicate with Cu(Ⅰ) ion, but also gives a double-stranded helicate with Cu(Ⅱ) ion. The results show that the linkage mode of the spacer group to the bipyridine units exerts a great impact on the formation of helix.