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 P 2 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. Two sets of Fe III/II complexes, 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, exhibit electronically asymmetrical ligands with metal-ligand orbital mixing.