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. 2020 Oct 16;10(63):38294-38303.
doi: 10.1039/d0ra07371g. eCollection 2020 Oct 15.

Syntheses, spectroscopic, redox, and structural properties of homoleptic Iron(III/II) dithione complexes

Kyle J Colston  1 , Sara A Dille  1 , Benjamin Mogesa  2 , Jacilynn Brant  3 , Victor N Nemykin  4 , Matthias Zeller  5 , Partha Basu  1
Affiliations

Syntheses, spectroscopic, redox, and structural properties of homoleptic Iron(III/II) dithione complexes

Kyle J Colston et al. RSC Adv. .

Abstract

Two sets of FeIII/II dithione complexes [FeII( i Pr2Dt0)3][PF6]2 ([1][PF6]2), [FeII(Me2Dt0)3][PF6]2 ([2][PF6]2), and [FeIII( i Pr2Dt0)3][PF6]3 ([3][PF6]3), [FeIII(Me2Dt0)3][PF6]3 ([4][PF6]3), and compound [FeIII( i Pr2Dt0)3][FeCl4][PF]2 ([3][FeCl4][PF6]2) were synthesized from N,N'-diisopropyl piperazine-2,3-dithione ( i Pr2Dt0) and N,N'-dimethyl piperazine-2,3-dithione (Me2Dt0) ligands. Complexes [1][PF6]2-[4][PF6]3 have been characterized by NMR, IR, and UV-visible spectroscopies, and by electrochemistry. The molecular structures of [2][PF6]2 and [3][FeCl4][PF6]2 have been determined by X-ray crystallography. Complexes [2][PF6]2 and [3][FeCl4][PF6]2 both crystallized in the monoclinic space group P21/n. Both complexes exhibit distorted octahedral geometry and the three coordinated ligands in each complex exhibit different dithione folding. Complexes [1][PF6]2-[4][PF6]3 exhibit a single FeIII/II based couple and three quasi-reversible ligand-based redox couples. The electronic spectra of [1][PF6]2-[4][PF6]3 show intense MLCT bands that indicate strong mixing between metal and ligand orbitals. DFT calculations were used to provide a framework for understanding the electronic origin of their redox chemistry and spectroscopic features.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Linear fit of the isotropic shift for [4][PF6]3 as a function of inverse temperature. Methylene CH2 protons are represented as ○ and methyl CH3 protons are represented as □. The signals for CH2 protons suggest significant delocalization of the spin density, δpara for both [3][PF6]3 and [4][PF6]3. Resonances for all protons (A-H) in variable temperatures are provided in Table S1.
Fig. 2
Fig. 2. Thermal ellipsoid plots (30%) of complex 2 (left) and 3 (right). Hydrogen atoms were omitted and only one conformation of the iPr substituents are shown for clarity. Refinement details of the iPr groups are described fully in the ESI.
Fig. 3
Fig. 3. Illustration of distortion with Θ with a projection along the C3 axis of a compound with Oh symmetry.
Fig. 4
Fig. 4. Cyclic voltammograms of the FeIII/II (left) and ligand-based (right) redox couples of [3][PF6]3 in an acetonitrile solution containing [Bu4N][PF6]. Recorded using a scan rate of 100 mV s−1 and a Pt disk working, Pt wire counter, and Ag+/Ag reference electrodes. Additional voltammograms are shown in ESI Fig. S5 and S6.
Fig. 5
Fig. 5. Electronic spectra of [1][PF6]2 (red), [2][PF6]2 (black), [3][PF6]3 (purple), and [4][PF6]3 (green) recorded in acetonitrile.
Fig. 6
Fig. 6. Frontier orbitals and energy diagrams of 1. Energies are relative and each molecular orbital is paired with its corresponding energy on the diagram. HOMO and LUMO are highlighted blue for clarity.
Fig. 7
Fig. 7. Mulliken spin density plot for 3.
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