Theoretical Analysis of the Jahn−Teller Distortions in Tetrathiolato Iron(II) Complexes

Abstract

Crystallographic studies of [Fe(SR)(4)](2-) (R is an alkyl or aryl residue) have shown that the Fe(II)S(4) cores of these complexes have (pseudo) D2d symmetry. Here we analyze the possibility that these structures result from a Jahn-Teller (JT) distortion that arises from the e(3z(2) - r(2), x(2) - y(2)) orbital ground state of Fe(II) in T(d)symmetry. Special attention is paid to the influence of the second-nearest neighbors of Fe, which lowers the symmetry and reduces the full JT effect to a smaller, pseudo JT effect (PJT). To estimate the size of the PJT distortion, we have determined the vibronic parameters and orbital state energies for a number of [Fe(SR)(4)](2-) models using density functional theory (DFT). Subsequently, this information is used for evaluating the adiabatic potential surfaces in the space of the JT-active coordinates of the FeS(4) moiety. The surfaces reveal that the JT effect of Fe(II) is completely quenched by the tetrathiolate coordination.

Shape and Spin State in Four‐Coordinate Transition‐Metal Complexes: The Case of the d6 Configuration

“…The S = 2 state is again the most stable one for the tetrahedron, with the optimized structure slightly deviating from the perfect tetrahedron (S(T d ) = 0.09, bond angles of 106 and 1118) due to a Jahn-Teller effect, as discussed recently by Vrajmasu et al [14] The relative energy of the square geometry for this spin state is now much higher compared to that of the methyl derivative (Figure 1). At the same time, the S = 1 and S = 0 states are strongly destabilized relative to the high spin situation, and only a triplet tetrahedral structure is expected for those compounds.…”

On the accuracy of density functional theory for iron—sulfur clusters

“…between the last two optimization steps. Each optimization started from the same initial wave function and geometry, which eliminated potential conformational differences between optimized structures, which can affect the electronic structure 48, 49…”

Density functional theory studies on the structure, vibrational spectra of three new tetrahalogenoferrate (III) complexes

“…Furthermore it was found that some iron (III) complexes provide a useful structural and electronic model for the similarly coordinated iron (III) sites found in the heme iron enzymes [9]. The tetrahalogenoferrates (III) have been utilized in bioinorganic chemistry as reagents for synthesizing some model compounds, such as [Fe 2 S 2 Cl 4 ] 2- [10,11]. The investiga-tion of the structures and properties of these compounds and their similarities are interested.…”