Heterometallic effects in tetrametallic triiron clusters

Heterometallic effects in metal-oxide clusters are of interest because of their relevance to both natural systems (heterometallic enzymic active sites such as Photosystem II) and artificial materials (mixed-metal oxide catalysts for energy conversion reactions such as dioxygen redn. and water oxidn.). In particular, the influence of Lewis acidic, redox-inactive metal centers on redox processes in many such systems is not fully understood. To gain insight into how redox-active metal clusters are modulated by redox-inactive metal centers, a series of tetranuclear oxo/hydroxo clusters were prepd. comprised of three Fe centers and a redox-inactive metal (M). These clusters were found to contain a Fe_3M(μ_4-O)(μ_2-OH) core (M = Ca, Sr, Zn, La, Sc), and were characterized by single-crystal X-ray diffraction, Mossbauer spectroscopy, and cyclic voltammetry. The effects of the redox-inactive metal centers on the properties and reactivity of these tetranuclear clusters will be discussed.