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

Two sets of Fe(III/II) dithione complexes [Fe(II)((i)Pr(2)Dt(0))(3)][PF(6)](2) ([1][PF(6)](2)), [Fe(II)(Me(2)Dt(0))(3)][PF(6)](2) ([2][PF(6)](2)), and [Fe(III)((i)Pr(2)Dt(0))(3)][PF(6)](3) ([3][PF(6)](3)), [Fe(III)(Me(2)Dt(0))(3)][PF(6)](3) ([4][PF(6)](3)), and compound [Fe(III)((i)Pr(2)Dt(0))(3)][FeCl(4)][PF](2) ([3][FeCl(4)][PF(6)](2)) were synthesized from N,N′-diisopropyl piperazine-2,3-dithione ((i)Pr(2)Dt(0)) and N,N′-dimethyl piperazine-2,3-dithione (Me(2)Dt(0)) ligands. Complexes [1][PF(6)](2)–[4][PF(6)](3) have been characterized by NMR, IR, and UV-visible spectroscopies, and by electrochemistry. The molecular structures of [2][PF(6)](2) and [3][FeCl(4)][PF(6)](2) have been determined by X-ray crystallography. Complexes [2][PF(6)](2) and [3][FeCl(4)][PF(6)](2) both crystallized in the monoclinic space group P2(1)/n. Both complexes exhibit distorted octahedral geometry and the three coordinated ligands in each complex exhibit different dithione folding. Complexes [1][PF(6)](2)–[4][PF(6)](3) exhibit a single Fe(III/II) based couple and three quasi-reversible ligand-based redox couples. The electronic spectra of [1][PF(6)](2)–[4][PF(6)](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.