Abstract
Herein, we report the syntheses of two lithium-vanadium oxide-fluoride compounds crystallized from the same reaction mixture through a time variation experiment. A low temperature hydrothermal route employing a viscous paste of V2O5, oxalic acid, LiF, and HF allowed the crystallization of one metastable phase initially, Li2VO0.55(H2O)0.45F5⋅2H2O (I), which on prolonged heating transforms to a chemically similar yet structurally different phase, Li3VOF5 (II). Compound I crystallizes in centrosymmetric space group, I2/a with a = 6.052(3), b = 7.928(4), c = 12.461(6) Å, and β = 103.99(2)°, while compound II crystallizes in a non-centrosymmetric (NCS) space group, Pna21 with a = 5.1173(2), b = 8.612(3), c = 9.346(3) Å. Synthesis of NCS crystals are highly sought after in solid-state chemistry for their second-harmonic-generation (SHG) response and compound II exhibits SHG activity albeit non-phase-matchable. In this article, we also describe their magnetic properties which helped in unambiguous assignment of mixed valency of V (+4/+5) for Li2VO0.55(H2O)0.45F5⋅2H2O (I) and +4 valency of V for Li3VOF5 (II).
Highlights
There has been a surge of research activities in the area of heteroanionic materials such as oxychalcogenides, oxynitrides, oxypnictides, and oxyhalides [1]
Often heteroanionic materials are more interesting than the pure homoanionic oxides, especially in the case of compounds with transition metals, where the presence of heteroanions influence the iono-covalency of bonds and oxidation state of the transition metal, often producing mixed valency [6,7]
One of the important systems of heteroanionic compounds that has been explored to some extent relates to vanadium oxyfluorides, which often contain a V = O terminal bond, especially at +4/+5 oxidation state, that can be exchanged with a fluoride under appropriate conditions [15,16,17,18,19]
Summary
There has been a surge of research activities in the area of heteroanionic materials such as oxychalcogenides, oxynitrides, oxypnictides, and oxyhalides [1]. The Poeppelmeir group has investigated this system in presence of sodium and other ions, which has resulted in materials that show interesting electrochemistry and second-harmonicgeneration (SHG) activities, respectively [17,18,19]. Synthesis of the latter producing the non-centrosymmetric (NCS) crystals exemplifies how the same reactant composition can lead to two different NCS crystals with varying amounts of fluorine as a function of time and temperature [19]. This investigation has led to the discovery of two new Li-V-oxy-fluoride phases with centrosymmetric and non-centrosymmetric structures of the compositions, Li2 VO0.55 (H2 O)0.45 F5 ·2H2 O (I)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
