Thermodynamics of the Cu^II μ‑Thiolate and Cu^I Disulfide Equilibrium: A Combined Experimental and Theoretical Study

The redox equilibrium between dinuclear Cu^II μ-thiolate and Cu^I disulfide structures has been analyzed experimentally and via DFT calculations. Two new ligands, L²SSL² and L⁴SSL⁴, and their Cu^II μ-thiolate and Cu^I disulfide complexes were synthesized. For L²SSL², these two redox-isomeric copper species are shown to be in equilibrium, which depends on both temperature and solvent. For L⁴SSL⁴ the μ-thiolate species forms as the kinetic product and further evolves into the disulfide complex under thermodynamic control, which creates the unprecedented possibility to compare both species under the same reaction conditions. The energies of the μ-thiolate and disulfide complexes for two series of related ligands have been calculated with DFT; the results rationalize the experimentally observed structures, and emphasize the important role that steric requirements play in the formation of the Cu^II thiolate structure.