Abstract
The electronic structure of multinuclear transition metal complexes is a highly challenging problem for quantum chemical methods. The problems to be solved for a successful analysis include the following: (1) many unpaired electrons leading to “highly entangled” wave functions that cannot be calculated by standard electronic structure methods, (2) drastic differences between the one-particle and many-particle spectra and a high density of low-lying states, and (3) the interpretation of such highly complex wave functions in chemical terms. In this work, we continue our research on oligonuclear clusters by presenting an in-depth analysis of the electronic structure of a prototypical iron–sulfur (Fe2S2) dimer. Accurate wave functions are obtained from a variety of advanced wave function based methods. The wave function results are interpreted in terms of an effective Hamiltonian that in turn is parametrized in terms of the angular overlap model (AOM) that provides the chemical insights that we are striving for. A hierarchical analysis allows us to interpret the local electronic structure in terms of the thiolate, sulfide ligands, and metal–metal interaction strengths. The many-particle spectrum is analyzed in terms of configurations involving ligand and metal centers. Finally, we are able to derive simple yet effective interpretations of ligand interaction strengths, the metal–metal interaction strength, and the low-lying many-particle spectrum of the Fe2S2 dimer.
Highlights
Iron−sulfur (FeS) active sites are well-known in nature to act as electron transfer agents in proteins.[1,2] The FeS dimer containing ferrodoxin proteins, which are recognized as model systems that carry out electron transfer, show interesting magnetic properties.[3−6] FeS dimers occur in the homovalent state with two equivalent tetrahedral Fe(III) sites,[2] whereas in its one-electron reduced state the dimer can occur as a mixedvalent localized Fe(II)−Fe(III) and a mixedvalent delocalized Fe(2.5)−Fe(2.5) dimer.[7]
The wave function results are interpreted in terms of an effective Hamiltonian that in turn is parametrized in terms of the angular overlap model (AOM) that provides the chemical insights that we are striving for
We have carried out a detailed analysis of the electronic structure of the iron−sulfur dimer
Summary
Iron−sulfur (FeS) active sites are well-known in nature to act as electron transfer agents in proteins.[1,2] The FeS dimer containing ferrodoxin proteins, which are recognized as model systems that carry out electron transfer, show interesting magnetic properties.[3−6] FeS dimers occur in the homovalent state with two equivalent tetrahedral Fe(III) sites,[2] whereas in its one-electron reduced state the dimer can occur as a mixedvalent localized (classes I and II) Fe(II)−Fe(III) and a mixedvalent delocalized Fe(2.5)−Fe(2.5) dimer.[7]. The effect of the metal−metal interaction on the electronic structure is presented by using our recently developed open-shell coupled cluster method.[15,16] In section 3.3, we present the many-particle spectrum of the dimer where the term “many-particle spectrum” is used to refer to the ab initio calculated eigenvalues of the Born−Oppenheimer Hamiltonian operator. This distinction is made in order to Received: April 3, 2019 Published: June 20, 2019.
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