The 57Fe Mössbauer quadrupole splittings (ΔEQ) and isomer shifts (δFe) in 3-coordinate high-spin Fe(II) complexes are unusually small, and previous attempts to reproduce their ΔEQ values have been unsuccessful. We show here that, by using large structural models and basis sets, both ΔEQ and δFe values can be quite accurately predicted by using density functional theory. Four systems were investigated: the three 3-coordinate species [LFeX]0 (L = β-diketiminate; X = Cl-, CH3-) and [Fe(SC6H2-2,4,6-tBu3)3]-, in addition to an uncommon 2-coordinate high-spin ferrous thiolate, [Fe(SC6H3-2,6-mes2)2] (mes = mesityl = 2,4,6-Me3C6H2). Both Gaussian-type-orbital and Slater-type-orbital basis sets were investigated, and both yielded ΔEQ and δFe values in good accord with experiment. There were no improvements in these property predictions when (approximate) relativistic effects were included in the calculations. An MO analysis provided a detailed picture of the origin of the small ΔEQ values seen in the 3-coordinate complexes. These results extend the scope of DFT/Mössbauer investigations beyond the 4-6-coordinate systems described previously to 2- and 3-coordinate systems, which should open the way to using these parameters in structure refinement, especially in large systems, such as proteins.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry