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Title: Electronic, magnetic structure and water splitting reactivity of the iron-sulfur dimers and their hexacarbonyl complexes: A density functional study

The iron sulfide dimers (FeS){sub 2} and their persulfide isomers with S–S bonds are studied with the B3LYP density functional as bare clusters and as hexacarbonyls. The disulfides are more stable than the persulfides as bare clusters and the persulfide ground state lies at 3.2 eV above the global minimum, while in the hexacarbonyl complexes this order is reversed: persulfides are more stable, but the energy gap between disulfides and persulfides becomes much smaller and the activation barrier for the transition persulfide → disulfide is 1.11 eV. Carbonylation also favors a non-planar Fe{sub 2}S{sub 2} ring for both the disulfides and the persulfides and high electron density in the Fe{sub 2}S{sub 2} core is induced. The diamagnetic ordering is preferred in the hexacarbonyls, unlike the bare clusters. The hexacarbonyls possess low-lying triplet excited states. In the persulfide, the lowest singlet-to-triplet state excitation occurs by electron transition from the iron centers to an orbital located predominantly at S{sub 2} via metal-to-ligand charge transfer. In the disulfide this excitation corresponds to ligand-to-metal charge transfer from the sulfur atoms to an orbital located at the iron centers and the Fe–Fe bond. Water splitting occurs on the hexacarbonyls, but not on the bare clusters.more » The singlet and triplet state reaction paths were examined and activation barriers were determined: 50 kJ mol{sup −1} for HO–H bond dissociation and 210 kJ mol{sup −1} for hydrogen evolution from the intermediate sulfoxyl-hydroxyl complexes Fe{sub 2}S(OH)(SH)(CO){sub 6} formed. The lowest singlet-singlet excitations in the hexacarbonyls, the water adsorption complexes and in the reaction intermediates, formed prior to dihydrogen release, fall in the visible light region. The energy barrier of 210 kJ mol{sup −1} for the release of one hydrogen molecule corresponds to one visible photon of 570 nm. The dissociation of a second water molecule, followed by H{sub 2} and O{sub 2} release via hydro-peroxide intermediate is a two-step process, with activation barriers of 218 and 233 kJ mol{sup −1}, which also fall in the visible light region. A comparison of the full reaction path with that on diiron dioxide hexacarbonyls Fe{sub 2}O{sub 2}(CO){sub 6} is traced.« less
Authors:
 [1] ;  [2]
  1. Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia 1113 (Bulgaria)
  2. Institute for Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9/E164-EC, 1060 Vienna (Austria)
Publication Date:
OSTI Identifier:
22419937
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 141; Journal Issue: 4; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ADSORPTION; ATOMS; CARBON MONOXIDE; DENSITY FUNCTIONAL METHOD; DIMERS; DISSOCIATION; DISULFIDES; ELECTRON DENSITY; ELECTRONS; EXCITATION; EXCITED STATES; GROUND STATES; HYDROGEN; IRON; IRON SULFIDES; ISOMERS; LIGANDS; MOLECULES; PHOTONS; WATER