A charge-transfer salt composed of methyl viologen and hexa­cyanidoferrate(II)

The methyl viologen dication, used under the name Paraquat as an agricultural reagent, is a well-known electron-acceptor species that can participate in charge-transfer (CT) inter­actions. The determination of the crystal structure of this species is important for accessing the CT inter­action and CT-based pro­perties. The title hydrated salt, bis­(1,1′-dimethyl-4,4′-bipyridine-1,1′-diium) hexa­cyanidoferrate(II) octa­hydrate, (C12H14N2)2[Fe(CN)6]·8H2O or (MV)2[Fe(CN)6]·8H2O [MV2+ is the 1,1′-dimethyl-4,4′-bipyridine-1,1′-diium (methyl viologen) dication], crystallizes in the space group P21/c with one MV2+ cation, half of an [Fe(CN)6]4− anion and four water mol­ecules in the asymmetric unit. The FeII atom of the [Fe(CN)6]4− anion lies on an inversion centre and has an octa­hedral coordination sphere defined by six cyanide ligands. The MV2+ cation is located on a general position and adopts a noncoplanar structure, with a dihedral angle of 40.32 (7)° between the planes of the pyridine rings. In the crystal, layers of electron-donor [Fe(CN)6]4− anions and layers of electron-acceptor MV2+ cations are formed and are stacked in an alternating manner parallel to the direction of the −2a + c axis, resulting in an alternate layered structure.