![]() The clusters feature a core assembly of iron and sulfur atoms typically denoted as z, where x and y > 1 and z denotes the charge of the cluster, that is anchored to the protein scaffold with cysteine residues. in hydrogenases ) but they also serve as the enzymatic reaction centers like in S-adenosyl- l-methionine reducing proteins that are involved in the DNA repair. Their key biological role is to mediate the electron transfer (e.g. Iron–sulfur clusters are ubiquitous in nature. ![]() By systematic extension of the donor orbital space we show that key excitations in the 300–800 nm range are of Fe 3d ← (μ-S) character. Moreover, the use of conventional configuration interaction methods enabled us to study the nature of the excited states in details with the difference density maps. We demonstrate that spin-averaged restricted open-shell Hartree–Fock orbitals are superior to high-spin orbitals and are convenient reference for subsequent configuration interaction calculations. In this work we present, for the first time, calculations of the electronic spectra of (SMe) 2− 4 biomimetic compound. Whereas low lying electronic excited states were subject of recent studies, higher energy states computed with many-body theories were never reported. Thus, the examples of the direct computations of electronically excited states of these systems are rare. The key complication in the electronic structure calculations of these compounds are the antiferromagnetic coupling of the iron centers and high covalency of Fe–S bonds. Based on ground-state orbitals and using the one electron transition picture, these bands are said to be of charge transfer character. The experimental UV–Vis spectra of the biologically relevant iron–sulfur clusters feature typically three bands in the 300–800 nm range. ![]()
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