Enhancing Temperature Sensitivity of Redox Potential via Redox-Induced Change in Copper Coordination Number by an External Ligand

High Resolution Image Download MS PowerPoint Slide We report a new design strategy for enhancing the temperature sensitivity of molecular redox potentials that is based on a redox-induced change in the metal coordination number facilitated by an external ligand. The Cu complex bis(2,9-dimethyl-1,10-phenanthroline)copper(II) binds coordinating ligands, including MeCN, whereas the Cu I analog remains tetracoordinate. Upon introduction of a stronger donor, 4- tert -butylpyridine ( t Bu-py), the MeCN ligand is displaced while retaining penta- and tetracoordination at the Cu II and Cu I centers, respectively. Variable-temperature electrochemical analysis reveals the temperature sensitivity of the apparent half-wave potential ( E 1/2 ) of the Cu II /Cu I couple to increase from α = 1.70(6) mV °C –1 to α = 2.3(2) mV °C –1 upon addition of 15.0 equiv of t Bu-py to the MeCN-bound Cu II complex in MeCN solution. Similar analysis starting with the Cu I complex affords α = 2.6(2) mV °C –1 in the presence of t Bu-py, providing a record-high temperature sensitivity of E 1/2 of the Cu II /Cu I couple in MeCN solution.