Syntheses and Physicochemical Properties of Low‐Melting Salts Based on VOF₄^– and MoOF₅^–, and the Molecular Geometries of the Dimeric (VOF₄^–)₂ and Mo₂O₄F₆^2– Anions

Abstract

1‐Ethyl‐3‐methylimidazolium (EMIm+) and N‐butylpyridinium (BPy+) salts of the oxotetrafluorovanadate (VOF4–) and oxopentafluoromolybdate (MoOF5–) anions with low melting temperatures have been synthesized by the reactions of the corresponding fluorohydrogenate ionic liquids and metal oxide fluoride. Differential scanning calorimetry reveals that the melting points of EMImVOF4, BPyVOF4, and BPyMoOF5 are 348, 346, and 346 K, respectively, whereas the room‐temperature ionic liquid EMImMoOF5 only exhibits a glass transition at 190 K. Density, viscosity, and ionic conductivity of EMImMoOF5 are 1.76 g cm–1, 86 cP, and 5.1 mS cm–1 at 298 K, respectively. The cathode and anode limits of EMImMoOF5 are –0.3 and +1.4 V (vs. Ag+/Ag), respectively. The molecular geometries of the VOF4– and Mo2O4F62– anions have been determined by single‐crystal X‐ray diffraction, the latter being obtained by the hydrolysis of MoOF5–. The two VOF4– anions in EMImVOF4 interact with each other through two highly asymmetric V–F···V bridges with V–F and V···F distances of 1.8633(7) and 2.3786(7) Å, respectively. A dinuclear anion in (BPy)2Mo2O4F6 possesses two symmetric Mo–F–Mo bonds with Mo–F lengths of 2.1691(12) and 2.1829(11) Å.

Electrochemical behavior of hexafluoroniobate, heptafluorotungstate, and oxotetrafluorovanadate anions in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide room temperature ionic liquid

“…6 shows Raman spectra of (a) BMPyrVOF 4 (solid), (b) 1.53 M BMPyrVOF 4 in BMPyrTFSA (liquid), and (c) BMPyrTFSA (liquid). The vibrational frequency of 1005 cm À1 in the Raman spectrum of BMPyrVOF 4 is assigned to the V5 5O stretching mode and is similar to that observed for EMImVOF 4 (1012 cm À1 in Raman spectrum), suggesting VOF 4 À forms a oligomeric unit as observed in the previous study [29]. The Raman spectrum (b) in Fig.…”

“…This suggests that these species diffuse in a totally different form in BMPyrTFSA. The similar case was also seen for NbCl 6 À and WCl 6 À [27,29]. The r s of VOF 4 À anion was calculated to be relatively small value of 0.12 nm.…”

“…Differential scanning calorimetry (DSC) revealed that its melting point is 323 K. According to the previous study on the crystal structures of CsVOF 4 [28] and EMImVOF 4 [29], VOF 4 À is not a discrete anion in the solid state but forms the polymeric or oligomeric unit (the (VOF 4 À ) n chain in CsVOF 4 and (VOF 4 À ) 2 dimer in EMImVOF 4 ) via a weak VÁÁÁF interaction. Fig.…”

Hydroxylammonium Tetrafluoridooxidovanadate(V) – (NH3OH)[VOF4]

“…Three different anions with the empirical formula VOF 4 -have been described in the literature, namely, the edge-sharing dimer 25,15 29 and in the present hydroxylammonium salt, a "helical" geometry is observed, which is identical to that of the conformer described in the Ag[VOF 4 ] crystal structure. This is reflected in the good agreement between geometric parameters of Figure 1.…”

Fluorohydrogenate Ionic Liquids, Liquid Crystals, and Plastic Crystals

“…Fluorohydrogenate ionic liquids work as a Lewis base when they are reacted with a fluoride (or oxidefluoride) which acts as a stronger Lewis acid than HF to liberate HF from (FH) n F − [69][70][71][72][73]. The following is the example of this reaction:…”