Tunable biomimetic chalcogels with Fe₄S₄ Cores and [Sn_nS_{2 n +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 Fe ₄S₄ clusters. We have investigated the effects of [Sn _nS_2n+2]^4- linking blocks ([SnS ₄]^4-, [Sn₂S₆]^4-, [Sn ₄S₁₀]^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)₃²⁺). The various thiostannate linking blocks do not alter significantly the chalcogel surface area (90-310 m²/g) or the local environment around the Fe₄S₄ clusters as indicated by ⁵⁷Fe Mössbauer 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 Fe₄S ₄ clusters are bridged with the adamantane [Sn₄S ₁₀]^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.