Evolution of the Electronic Structure of the trans-[Re6S8bipy4Cl2] Octahedral Rhenium Cluster during Reduction

Abstract

Understanding the processes that occur during the redox transformations of complexes coordinated by redox-active apical ligands is important for the design of electrochemically active compounds with functional properties. In this work, a detailed analysis of the interaction energy and electronic structure was performed for cluster complexes trans-[Re₆S₈bipy₄Cl₂]ⁿ (n = 2-, 4-, 6-, 8-), which can be obtained by stepwise electrochemical reduction of a neutral cluster trans-[Re₆S₈bipy₄Cl₂] in DMSO solution. It was shown that the formation of open-shell paramagnetic ions with S = 1, 2 and 1 is the most energetically favorable for n = 2-, 4- and 6-, respectively.

Keywords: DFT; ELF; cyclic voltammetry; octahedral rhenium clusters; reduction.

Figure 1

The structure of the trans-[Re₆S₈bipy₄Cl₂] cluster. The hydrogen atoms of bipyridine ligands are removed for clarity.

Figure 2

The diagram of the energy levels and isosurfaces of the MOs for the [Re₆S₈bipy₄Cl₂]⁰ cluster.

Figure 3

E½ (V) vs. ΔE (eV) plot for S12g/TZP (♦) and S12h/TZ2P//S12g/TZP (■) levels of theory.

Figure 4

Schematic representation of the four lowest unoccupied orbitals formation starting from the LUMO of the bipy, through the LUMO, LUMO + 1, LUMO + 2, and LUMO + 3 orbitals of the bipy₄ fragment, to the LUMO, LUMO + 1, LUMO + 2, and LUMO + 3 orbitals of the [Re₆S₈bipy₄Cl₂]⁰ cluster.

Figure 5

Occupation of the frontier orbitals during the reduction of the [Re₆S₈bipy₄Cl₂]ⁿ clusters.

Scheme 1

Changes in the charges and spin states during eight-electron reduction of the [Re₆S₈bipy₄Cl₂]⁰ cluster.

Figure 6

The relationship between V(Re,N_in) basin populations and the interaction energies (E_int) between Re₆S₈Cl₂ and [bipy₄]ⁿ fragments in the [Re₆S₈Cl₂bipy₄]ⁿ (n = 0, 2–, 4–, 6– and 8–) clusters.