Experimental charge density analysis of symmetrically substituted ferrocene derivatives

Experimental charge density analysis of three symmetrically substituted ferrocene derivatives: 1,1'- dimethyl ferrocene (1), decamethyl ferrocene (2), and 1,1'-diacetyl ferrocene (3) was conducted. The electron donating or accepting propensities of the ferrocene substituents were evaluated. The metal ligand interactions in all analyzed compounds were found to be similar in terms of charge density concentrations at Bond Critical Points (BCPs), laplacian values, and deformation density features. The monopole population of iron in all cases tend to be slightly negative, suggesting charge donation from Cp ligands. d orbital populations in all cases adopt values in agreement with theoretical calculations and ligand field theory. The charge distribution over analyzed molecules does not correlate with the formal oxidation potential in the analyzed compounds, as compound 2 in the currently studied structure takes the place suitable for an unsubstituted ferrocene. The non-intuitive low energy of the eclipsed conformation of 1 compound finds some explanation in the existence of a bond critical point between atoms of the two methyl groups in the structure. An asymmetry of the atomic surroundings of the two oxygen atoms in the 3 structure, reflected by the differences in charge rho(r(BCP)) and nabla(2)rho(r(BCP)) values and the shape of deformation density in the regions of oxygen lone electron pairs, is described.