Intramolecular hydrogen bonding interaction, a mechanism for the bridging linkages to exert electronic influence on diiron models of [FeFe]-hydrogenase

Seven diiron hexacarbonyl complexes, [Fe2(L)(CO)6](L = two monothiolate or dithiolate ligands), as the mimics of the diiron subunit of [FeFe]-hydrogenase were theoretically investigated using density functional theory (DFT) to examine the electronic influences of the bridging linkages of the complexes on their electrochemical behaviours. In the calculations, the energies, the compositions of the frontier orbitals and the one-electron redox potentials of these complexes were estimated. Charge distributions of the complexes were calculated using natural population analysis (NPA). The influence of the functional groups of the bridging linkages on the diiron core via intramolecular hydrogen interactions was explored using topological analysis. The results indicated that the bridging linkages of the complexes affect significantly the compositions of the HOMOs whereas hardly alter the compositions of the LUMOs. The correlations of the energies of the frontier orbitals to the redox potentials of the examined complexes were also discussed.