Tunable Biomimetic Chalcogels with Fe4S4 Cores and [SnnS2n+2]4-(n=1, 2, 4) Building Blocks for Solar Fuel Catalysis

Biology sustains itself by converting solar energy in a series of reactions between light harvesting components, electron transfer pathways, and redox-active centers. As an artificial system mimicking such solar energy conversion, porous chalcogenide aerogels (chalcogels) encompass the above components into a common architecture. We present here the ability to tune the redox properties of chalcogel frameworks containing biological Fe4S4 clusters. We have investigated the effects of [SnnS2n+2](4-) linking blocks ([SnS4](4-), [Sn2S6](4-), [Sn4S10](4-)) on the electrochemical and electrocatalytic properties of the chalcogels, as well as on the photophysical properties of incorporated light-harvesting dyes, tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)). The various thiostannate linking blocks do not alter significantly the chalcogel surface area (90-310 m(2)/g) or the local environment around the Fe4S4 clusters as indicated by Fe-57 Mossbauer spectroscopy. However, the varying charge density of the linking blocks greatly affects the reduction potential of the Fe4S4 cluster and the electronic interaction between the clusters. We find that when the Fe4S4 clusters are bridged with the adamantane [Sn4S10](4-) linking blocks, the electrochemical reduction of CS2 and the photochemical production of hydrogen are enhanced. The ability to tune the redox properties of biomimetic chalcogels presents a novel avenue to control the function of multifunctional chalcogels for a wide range of electrochemical or photochemical processes relevant to solar fuels.