A solvent-dependent and electrochemically controlled self-assembling/disassembling system.

The bis-bidentate ligand R,S-1,2-diphenyl-N,N'-bis(2-quinolinemethylidene) ethane-1,2- diamine (ligand 4), containing two (iminomethyl) quinoline moieties separated by a cis-1,2-diphenylethylene spacer, forms stable complexes with both Cu-I and Cu-II. With Cu-II, the monomeric 1: 1 complex [Cu-II (4)](2+) is obtained both in CH3CN and CH2Cl2. With Cu-I and overall 1: 1 metal/ligand molar ratio, an equilibrium mixture is obtained in CH3CN, consisting of [Cu-I (4)(2)](+), [Cu-2(I) (4)(2)](2+) and [Cu-2(I) (4)(CH3CN)(4)](2+). The preponderant species is the two-metal one-ligand "open" complex [Cu-2(I) (4)(CH3CN)(4)](2+), in which each Cu+ cation is coordinated in a tetrahedral fashion by one (iminomethyl) quinoline unit and by two CH3CN molecules. Precipitation from the equilibrium mixture yields only crystals of [Cu-2(I) (4)(CH3CN)(4)](ClO4)(2).2CH(3)CN, whose crystal and molecular structures have been determined. On the other hand, in the poorly coordinating CH2Cl2 solvent, only the dimeric helical [Cu-2(I) (4)(2)](2+) complex is obtained, when the overall metal/ligand 1: 1 molar ratio is chosen. Addition of large quantities of acetonitrile to solutions of [Cu-2(I) (4)(2)](2+) in dichlorometane results in the formation of [Cu-2(I) (4)(CH3CN)(4)](2+), i. e. in the solvent-driven disassembling of the Cu-I helicate. While electrochemistry in CH3CN is poorly defined due to the presence of more than one Cu-I species, cyclic voltammetry experiments carried out in CH2Cl2 revealed a well defined behavior, with irreversible oxidation of [Cu-2(I) (4)(2)](2+) and irreversible reduction of [Cu-II (4)](2+) taking place at separate potentials (DeltaE approximate to 700 mV). Irreversibility and separation of the redox events are due to the self-assembling and disassembling processes following the reduction and oxidation, respectively