Dicopper double-strand helicates held together by additional π-π interactions.

The bis-bidentate ligand, obtained from Schiff base condensation of RR-1,2-cyclohexanediamine and 8-naphthylmethoxyquinoline-2-carbaldehyde (L–L), forms with [CuI(MeCN)4]ClO4 a double strand helicate complex, made especially stable by the presence of four definite interstrand π–π interactions involving a quinoline subunit and a naphthylmethoxy substituent of the two strands. The [CuI2(L–L)2]2+ complex, which does not decompose even on excess addition of either L–L or CuI, undergoes a two electron oxidation in MeCN, through two one-electron fully reversible steps, separated by 260 mV, as shown by cyclic voltammetry (CV) studies. The high stability of the mixed valence complex [CuICuII(L–L)2]3+ with respect to disproportionation to [CuI2(L–L)2]2+ and [CuII2(L–L)2]4+ is essentially due to a favorable electrostatic term. CuII forms with L–L a stable species, with a 1:1 stoichiometric ratio, but, in the absence of crystallographic data, it was impossible to assess whether it is of mono- or dinuclear nature. Ho...