Special CCE Seminar

Redox-inactive metals are found in biological and heterogeneous water oxidation catalysts, but their roles are currently not well understood. Additionally, heterogeneous mixed transition metal oxides are emerging as good catalysts for oxygen reduction and evolution. With current schemes of energy conversion involving water oxidation and dioxygen reduction, a detailed understanding of these systems is imperative for the rational development of practical catalysts. Targeting synthetic model clusters of these catalysts, multinucleating ligands were developed for Earth abundant first-row transition metals (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺). Trimetallic complexes were utilized as precursors to more elaborate metal oxide clusters. Tetranuclear complexes displaying Mn₄, Mn₃Ca and other Mn₃M motifs with varied number of bridging oxo ligands were synthesized. The reduction potentials of these clusters span a window of over 1 V. With the pK_a of the redox-inactive metal-aqua complex as a measure of Lewis acidity, structurally analogous series of clusters display linear dependence between reduction potential and acidity. These findings provide a general strategy for tuning the clusters over a wide range of potentials and reactivity modes. Implications for the function of oxygen evolving and reduction catalysts will be discussed.