| Abstract
| - The new ligands R,R-trans-S,S‘-bis[methyl(2‘-quinolyl)]-1,2-dithiacyclohexane, cis-S,S‘-bis[methyl(2‘-quinolyl)]-1,2-dithiacyclohexane, and 1,6-bis(2‘-quinolyl)-2,5-dithiahexane have been synthesized and their complexes with CuIand CuII prepared. The ligand/metal systems are bistable, as the complexes with copper in both its oxidation statesare stable under the same conditions as solids and in solution. The crystal and molecular structure of [CuI(1,6-bis(2‘-quinolyl)-2,5-dithiahexane)]ClO4 has been determined by X-ray diffraction and reveals that the complex ismonomeric, with the ligand folding around the Cu+ cation, imparting to it a tetrahedral coordination. UV−vis, MS-ESI, and NMR data indicate that the same is found for the CuI complexes of all three ligands. Also, the CuIIcomplexes are monomeric, but with a square arrangement of the ligands around Cu2+. On changing the oxidationstate, the change in the geometrical arrangement is fast and complete in less than 80 ms, as demonstrated bycyclic voltammetry experiments. In the CV profiles, the oxidation and reduction events take place at separated Eoxand Ered values, with no return wave even at the fastest scan rates. In the Eox−Ered interval (which ranges from 450to 650 mV, depending on the ligand), the ligand/copper system can thus exist in one of its two states, dependingon its history, and thus display electrochemical hysteretical behavior. The electrochemical cycle leading from thetetrahedral [CuI(ligand)]+ to the square [CuII(ligand)]2+ complex (and vice versa) is reversible and repeatable withoutdegradation, as checked by coupled UV−vis-controlled potential coulometry experiments.
- Three new bis-thia-bis-quinoline tetradentate ligands form bistable systems with copper. Both CuI and CuII complexes are stable under the same conditions, in solution and in the solid. Both forms are monomeric and can be reversibly interconverted electrochemically. However, such significant rearrangements follow the redox events that the oxidation and reduction waves are separated and the systems show electrochemical hysteresis.
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