[Zurück]

E. Uzunova, H. Mikosch:
"Electronic, Magnetic Structure and Water Splitting Reactivity of the Iron-Sulfur Dimers and their Hexacarbonyl Complexes: a Density Functional Study";
Journal of Chemical Physics, 141 (2014), 4; S. 044307 - 044307-14.

The iron sulfide dimers (FeS)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 Fe2S2 ring for both the disulfides and the persulfides and high electron density in the Fe2S2 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 S2 via metal-to-ligand charge transfer (MLCT). In the disulfide this excitation corresponds to ligand-to-metal charge transfer (LMCT) 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. The singlet and triplet state reaction paths were examined and activation barriers were determined: 50 kJ mol-1 for HO-H bond dissociation and 210 kJ mol-1 for hydrogen evolution from the dihydroxyl complexes formed. A comparison of the reaction path with the diiron dioxide hexacarbonyls Fe2O2(CO)6 is presented.

Water splitting, Singlet-triplet excitations, Iron-Sulfur dimers, Electronic Structure

http://dx.doi.org/10.1063/1.4890650

http://publik.tuwien.ac.at/files/PubDat_227769.pdf