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

Abstract

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, (CHN)[Fe(CN)]·8HO or (MV)[Fe(CN)]·8HO [MV is the 1,1'-dimethyl-4,4'-bipyridine-1,1'-diium (methyl viologen) dication], crystallizes in the space group P2/c with one MV cation, half of an [Fe(CN)] anion and four water molecules in the asymmetric unit. The Fe atom of the [Fe(CN)] anion lies on an inversion centre and has an octahedral coordination sphere defined by six cyanide ligands. The MV 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)] anions and layers of electron-acceptor MV 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.

Unique Hydration/Dehydration-Induced Vapochromic Behavior of a Charge-Transfer Salt Comprising Viologen and Hexacyanidoferrate(II)

“…The diffuse-reflectance spectra of 1-Wet and 1-Dry are shown in Figure . It is known that CT salts composed of viologen and [Fe­(CN) 6 ] 4– display absorption bands in the visible region that correspond to intermolecular CT transition; ,, 1-Wet and 1-Dry exhibit absorption bands at 560 and 507 nm, respectively, which we assign to their intermolecular CT transitions. The band shift observed as 1-Wet transformed into 1-Dry suggests that each crystal phase exhibits different intermolecular CT interactions.…”

“…Charge-transfer (CT) salts are known to exhibit physical properties based on intermolecular CT interactions, such as electric conduction and magnetism, among others. − The salt of methyl viologen (MV 2+ , 1,1′-dimethyl-4,4′-bipyridine-1,1′-diium) and hexacyanidoferrate­(II), (MV) 2 [Fe­(CN) 6 ]·8H 2 O, is one such CT salt. − In Prussian blue, one of the most famous intervalence CT compounds, the [Fe­(CN) 6 ] 4– species acts as the electron-donor, while MV 2+ is a well-known electron-acceptor that readily forms intermolecular CT compounds with electron-donating species . While both [Fe­(CN) 6 ] 4– and MV 2+ ions are colorless, the CT salt of MV 2+ and [Fe­(CN) 6 ] 4– exhibits deep colors based on CT interactions; deep blue in the solid phase and red-purple in aqueous solution.…”

“…While both [Fe­(CN) 6 ] 4– and MV 2+ ions are colorless, the CT salt of MV 2+ and [Fe­(CN) 6 ] 4– exhibits deep colors based on CT interactions; deep blue in the solid phase and red-purple in aqueous solution. These observations stimulated our interest in the colors of CT salts composed of organic acceptor cations and [Fe­(CN) 6 ] 4– . , …”

“…These observations stimulated our interest in the colors of CT salts composed of organic acceptor cations and [Fe(CN) 6 ] 4− . 4,8 Herein, a new CT salt of ethyl viologen (EV 2+ , 1,1′-diethyl-4,4′-bipyridine-1,1′-diium) and the [Fe(CN) 6 ] 4− anion was prepared, because the modification of viologen was expected to induce changes in crystal packing and intermolecular CT interaction. The (EV)(H 3 O) 2 [Fe(CN) 6 ] salt obtained in this manner (1-Wet), contains two oxonium ions (H 3 O + ).…”

Design, Synthesis, Crystal Structure and Photophysical Properties of New Oxadiazole Extended Viologen Fluorophore

“…Considering the vast number of applications of viologens, it is important to analyze the crystal structures of viologens to assess the important information about charge transfer interaction, distance between the electron donor and acceptor, packing of cations and anions in the molecule and its effect on fluorescence, photoswitching properties. Very few studies have been reported on the X-ray diffraction analysis of these molecules [17] [18] [19] [20]. Herein, we report the synthesis, crystal structure and photophysical properties of N,N'-dimethyl-2,5-Bis(pyridinium)oxadiazole 4 and its precursor 2,5-Bis(pyridine)oxadiazole 2.…”