Structural and Electronic Rearrangements in Fe₂S₂, Fe₃S₄, and Fe₄S₄ Atomic Clusters under the Attack of NO, CO, and O₂

Abstract

We report results, based on density functional theory− generalized gradient approximation calculations, that shed light on how NO, CO, and O 2 interact with Fe 2 S 2 , Fe 3 S 4 , and Fe 4 S 4 clusters and how they modify their structural and electronic properties. The interest in these small iron sulfide clusters comes from the fact that they are at the protein cores and that elucidating fundamental aspects of their interaction with those light molecules which are known to modify their functionality may help in understanding complex behaviors in biological systems. CO and NO are found to bind molecularly, leading to moderate relaxations in the clusters, but nevertheless to changes in the spin-polarized electronic structure and related properties. In contrast, dissociative chemisorption of O 2 is much more stable than molecular adsorption, giving rise to significant structural distortions, particularly in Fe 4 S 4 that splits into two Fe 2 S 2 subclusters. As a consequence, oxygen tends to strongly reduce the spin polarization in Fe and to weaken the Fe−Fe interaction inducing antiparallel couplings that, in the case of Fe 4 S 4 , clearly arise from indirect Fe−Fe exchange coupling mediated by O. The three molecules (particularly CO) enhance the stability of the iron−sulfur clusters. This increase is noticeably more pronounced for Fe 2 S 2 than for the other iron−sulfur clusters of different compositions, a result that correlates with the fact that in recent experiments of CO reaction with Fe m S m (m = 1−4), the Fe 2 S 2 CO product results as a prominent one.

Interaction Study of Oxygen and Iron-Sulfur Clusters Based on the Density Functional Theory

“…e cluster structure was then optimized and the result is shown in Figure 2(b). e optimized cluster structure was compared with previous research data [10] to confirm the reasonableness of the calculation method and structure used in this work, and the results of the comparison are provided in the supporting information. M denotes the spin multiplet degree.…”

“…For example, parameters such as vertical ionization potential (VIP) and adiabatic electron affinity energy (AEA) differ greatly from experimental values. Amitouche et al [10], Li et al [11], and Yin et al [12] tested the structure of the iron-sulfur system using a variety of generalized functions in combination with basis groups. Among them, the B3LYP generalized function and the PBE generalized function agree well with the experimental values, and these two generalized functions are consistent in describing the spin states of the iron-sulfur clusters, but both methods underestimate the experimental values of the interatomic distances in terms of structural properties.…”

First-Principles Perspective on Gas Adsorption by [Fe4S4]-Based Metal–Organic Frameworks

“…In all cases, the oxidized product is more stable than the reactants and the corresponding adsorbate–adsorbent complex before the reaction. These observations agree with the Amitouche et al . results where dissociative O 2 chemisorption on [Fe 4 S 4 ] was found to be more stable than its non-dissociative physical adsorption.…”

DFT Studies of Cubane [4Fe-4S]2+/3+ Clusters: J-Aggregates of FeS Tetramers

“…These low spin clusters are different and we expect they will function differently in the adsorption of gas phase molecules than the high spin clusters. 86 For the singlet [4Fe-4S] 2+ , it does no longer resemble the J aggregates of FeS at high spin states. Rather, it is a tetramer Fe cluster (Fe4) ligated with an S atom on each surface.…”