Role of redox-inactive metals in controlling the redox potential of heterometallic manganese–oxido clusters
Keisuke Saito, Minesato Nakagawa, Manoj Mandal, Hiroshi Ishikita
Abstract
Abstract Photosystem II (PSII) contains Ca 2+ , which is essential to the oxygen-evolving activity of the catalytic Mn 4 CaO 5 complex. Replacement of Ca 2+ with other redox-inactive metals results in a loss/decrease of oxygen-evolving activity. To investigate the role of Ca 2+ in this catalytic reaction, we investigate artificial Mn 3 [M]O 2 clusters redox-inactive metals [M] ([M] = Mg 2+ , Ca 2+ , Zn 2+ , Sr 2+ , and Y 3+ ), which were synthesized by Tsui et al. (Nat Chem 5:293, 2013). The experimentally measured redox potentials ( E m ) of these clusters are best described by the energy of their highest occupied molecular orbitals. Quantum chemical calculations showed that the valence of metals predominantly affects E m (Mn III/IV ), whereas the ionic radius of metals affects E m (Mn III/IV ) only slightly.