Alkali Metal Mediated Redox Tuning in Bis(μ-OH) Dinickel(II) Complexes.

Redox-inactive metal ions act in tandem with redox-active transition metals in biological, molecular, and solid-state systems to precisely tune reactivity. Notwithstanding, mildly Lewis acidic alkali cations are rarely studied in this context, despite their prevalence in both cellular and electrochemical media. Herein, we disclose a structurally characterized series of monovalent Lewis acids (Li+, Na+, K+, and Cs+) adducted to a bis(μ-OH) dinickel diamond core. Spectroscopic characterization demonstrates that the oxygenic binding pocket of the tripodal NNNO-chelate maintains this structure in solution. Detailed electrochemical measurements establish trends correlating oxidation potential and alkali metal identity, demonstrating a steep dependence on Lewis acidity (∼165 mV/pKa decade). Density functional theory indicates that the observed oxidation chemistry is largely ligand-centered, highlighting the importance of electronic coupling between the Lewis acid and locus of redox. These findings, with relevance to bioinorganic, heterogeneous, and molecular oxidation processes, provide design criteria for rationalizing and maximizing the impact of relatively weak Lewis acids, including common alkali cations, on the physicochemical properties of redox-active species.