Molecular Switching of Copper Complexes with Quaterpyridine

Chemically and electrochemically induced interconversion between five one-stranded complexes of copper(II) and the respective double-stranded helicates of copper(I) bearing the ligand 6,6'''-dimethyl-2,2': 6', 2 '': 6 '', 2'''-quaterpyridine (L) culminated in different luminescence properties. Five new mononuclear complexes of copper(II) bearing the ligand L {[(CuLCl2)-L-II] (1), [(CuL)-L-II(ClO4)(2)] (2), [(CuL)-L-II(NO3)(2)] (3), [(CuL)-L-II(CF3SO32] (4), and (CuL)-L-II(BF4)(2)] (5)} have been reduced in two different ways: The first, by using metallic copper, gave [(Cu2L2)-L-I][(CuCl4)-Cl-II] (1a), [(Cu2L2)-L-I][Cu-II(ClO4)(4)] (2a), and [(Cu2L2)-L-I][Cu-II(NO3)(4)] (3a), and the second, by using ascorbic acid, led to [(Cu2L2)-L-I(CF3SO3)(2)] (4a) and [(Cu2L2)-L-I(BF4)(2)] (5a). The conversion of the helicates into mononuclear complexes can be implemented by oxidation with hydrogen peroxide or by the displacement of Cu-I by Cu-II ions.