New Publication – Solvent Effects on a Two-Electron Redox Cycle

Rezoanul Islam’s latest work was published in Inorganic Chemistry, detailing the role solvent coordination on the two-electron Ni(IV/II) redox cycle of nickel bis(diethyldithiocarbamate). https://pubs.acs.org/doi/full/10.1021/acs.inorgchem.4c02024

Our previous work had shown that pyridine can coordinate the intermediate Ni(III) redox state when oxidized electrochemically from Ni(II). This new publication shows how the solvent coordination ability, measured by the donor number, directly influences the rate at which Ni(III) is converted to Ni(IV) via disproportionation. Solvents with higher donor numbers, like pyridine, slow this rate while solvents with lower donor numbers enhance this rate. Interestingly, solvents with no coordination ability like dichloromethane still show conversion to Ni(IV), but through a sequential one-electron EEC process instead of a two-electron ECE process, showing that solvent coordination is critical to achieving a single two-electron redox wave in the cyclic voltammogram. Temperature dependent CV data also measured the enthalpy and entropy of activation for the chemical step in the ECE cycle, showing a net associative rate-limiting step. We therefore proposed that this step must occur via the merging of Ni(III) and Ni(II) complexes to facilitate the exchange of a diethyldithiocarbamate ligand.