Preparation and Crystal Structure of a New Lithium Vanadium Fluoride Li₂VF₆ with Trirutile-type Structure

Abstract

A new lithium vanadium fluoride Li 2 VF 6 was prepared by reacting lithium fluoride LiF with vanadium tetrafluoride VF 4 in a monel capsule at 500 • C. The crystal structure has been determined by means of powder X-ray diffraction. Trirutile-type dilithium hexafluorovanadate(IV) crystallizes in the tetragonal space group P4 2 /mnm with lattice parameters a = 459.99(1), b = 459.99(1), c = 896.64(2) pm. The presence of a Jahn-Teller effect is discussed.

Exploratory Synthesis for Complex Metal Fluorides Using Solid-State Fluorine Sources

“…In addition, for M = Ti, a small amount of β-Li 3 TiF 6 was also obtained as the secondary phase. For M = V, we could not obtain Li 2 VF 6 , resulting in Li 3 VF 6 with trivalent V as the main phase and a small amount of VF 3 and unknown phases as secondary phases. Although VF 4 is likely to be available with the reaction between V and CuF 2 based on the data in Table S1, this result implies that Li 3 VF 6 is more stable than Li 2 VF 6 under the synthetic condition used.…”

“…In the case of M = Nb, Li 2 ZrF 6 -type Li 2 NbF 6 appeared by synthesis even under 7.7 GPa, and additional unknown phases were observed. It was reported that the phase relations of Li 2 MF 6 at room temperature and high pressure were correlated with the ionic radius of tetravalent cation r M 4+ , and at ambient pressure, the structure type changes as follows: Na 2 SiF 6 -type, r M 4+ < 0.54 Å; trirutile-type, 0.54 Å < r M 4+ < 0.71 Å; Li 2 ZrF 6 -type, r M 4+ > 0.71 Å. , In fact, the structure adopting Li 2 MF 6 (M = Ti, V, Zr, Nb, and Mo) is in agreement with the above phase relation except for Li 2 NbF 6 : trirutile-type for M = V (ionic radius in six-fold coordination, r M 4+ (VI): 0.58 Å), Ti (0.605 Å), and Mo (0.650 Å) and Li 2 ZrF 6 -type for Nb (0.68 Å) and Zr (0.72 Å). Based on previous reports and the results in this study, we summarized the stability range of polymorphism of Li 2 MF 6 including Li 2 MoF 6 at ambient pressure and under high pressure in Figure .…”

“…In the present study, we apply these techniques in our first attempt at synthesizing a complex metal using metals and solid-state fluorine sources. Namely, we attempt to synthesize known compounds, Li 2 MF 6 , with the tetravalent early transition-metal ions as M (M = Ti, − V, Nb, Zr, , and Mo , ); some of these target compounds, such as Li 2 TiF 6 and Li 2 VF 6 , are candidates for active materials in Li-ion batteries. These compounds have been synthesized using metal fluorides or by means of fluorination of oxides using F 2 gas or HF aqueous solution, and there has been no attempt to synthesize them using solid-state fluorine agents such as CuF 2 .…”