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À propos de : Electrochemical Assembling/Disassembling of Helicates with Hysteresis        

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  • Electrochemical Assembling/Disassembling of Helicates with Hysteresis
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  • A series of eight tetradentate, ditopic, bisimino bisheterocyclic ligands (1−8), and their complexes with CuI andCuII, have been studied in CH3CN solution, by means of 1H NMR, mass, and UV/vis spectroscopy, while thecrystal and molecular structure of the CuII complexes [Cu(3)](CF3SO3)2 and [Cu(4)](CF3SO3)2 and of the CuIcomplexes [Cu2(4)2](ClO4)2 and [Cu2(5)2](ClO4)2 have been determined by X-ray diffraction methods. The CuIIcomplexes are monomeric, almost square-planar structures, both in solution and in the solid state, while the CuIcomplexes are two-metal, two-ligand dimers which can be both helical and “box-like” in the solid, while theyadopt a simple helical configuration in acetonitrile solution. The systems made of ligands 1−8 and copper arebistable, as under the same conditions either the CuI helical dimers or the CuII monomers can be obtained and arestable. The electrochemical behavior of the 16 copper complexes has been studied in acetonitrile solutions bycyclic voltammetry. One reduction and one oxidation wave were found in all cases, which display no return waveand are separated by a 500−1000 mV interval. Irreversibility is due to the fast self-assembling process that followsthe reduction of [CuII(L)]2+ and to the fast disassembling process that follows the oxidation of [CuI2(L)2]2+(L = 1−8). However, the overall [oxidation+disassembling] or [reduction+self-assembling] processes, i.e.,[CuI2(L)2]2+ = 2[CuII(L)]2+ + 2e-, are fully reversible. Moreover, CV profiles show that solutions containingcopper and L undergo hysteresis on changing the applied electrochemical potential: in the same potential interval,the systems can exist in solution as either [CuI2(L)2]2+ or [CuII(L)]2+, depending on the electrochemical historyof the solution. Moreover, by changing the structural or donor features of the ligands it is possible to modulatethe potentials at which the system undergoes a transition from one to the other of its two possible states, in thehysteresis cycle. In addition, the spectral properties of the CuI and CuII complexes of the considered ligands makethese systems good candidates for storing information in solution, which can be electrochemically written orerased and spectroscopically read.
  • A series of eight ligands have been prepared, whose electrochemical behavior in the presence of copper presents hysteresis. In the same range of potentials either CuI helical dimers or CuII square-planar monomers can actually exist, depending on the electrochemical history of the solution. The variation of structural and donor features of the ligands allows the modulation of the potentials at which transitions between the two states take place in the hysteresis cycle.
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