Hexanuclear rhenium chalcohalide clusters

It seems natural to suppose that the tetragonal distortion of the tri-anion results from the Jahn-Teller effect. In order to study the problem more thoroughly we undertook recently the DFT calculations of this cluster as well as of several other hexanuclear rhenium chalcohalide clusters. The technical details of these calculations can be found in the original publication [8]. Here we only want to note that the introduction of relativistic corrections for Re atoms is crucial for the correct reproduction of the geometry of clusters. In our calculations, this was done by the zero order regular approximation (ZORA) Hamiltonian [9] within ADF 2000.02 package [10]. 

Calculations of the tetra-anionic cluster Re6SxCI6 4 have been done in the symmetry group Oh. All attempts to lower the symmetry converged again to the same geometry. The structural parameters obtained as a result of the optimization are in good agreement with the structural data. We found 3.684 A for the opposite Re-Re distances, 2.436 and 2.486 A for Re-S and Re-Cl bonds, respectively. 

The average experimental values are equal to 3.681, 2.404, and 2.451 A. The rhenium-rhenium distances are well reproduced and the rhenium-ligand distances are slightly longer than the experimental ones (the difference does not exceed 1.5%). The experimental data show that the structure of the rhenium core remains unchanged for all closed shell clusters. At the same time, it has been reported that the Re-Cl distances strongly depend on the nature of the counter-cation in the salt. This shows that the rhenium-apical ligand bonds are very sensitive to the effects of environment. Our calculations in gas phase do not take into account the crystal 

Concluding this paragraph we can note that DFT methods can give important qualitative and quantitative results for vibronic effects in polynuclear clusters. However, as for mononuclear complexes the DFT methods can be used with a special care for Jahn-Teller systems. 

Since the excess electron is localized on nondegenerate orbital the excess electron vibronic interaction is limited to the totally symmetric distortions of the first coordination sphere. This interaction reflects the difference of metal-ligand distances in different oxidation states. The matrix of the electron-vibrational interaction is diagonal on the basis of localized states with the matrix elements 

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Hexanuclear chalcohalide Rhenium(III) clusters UV-Vis B3LYP, PBEIPBE, B2PLYP/ LanL2DZ CPCM 100... 

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