Anomalously Large Formula Unit Volume and Its Effect on the Thermal Behavior of LiBF₄

Abstract

The crystal structure of LiBF4 has been determined by single-crystal X-ray diffraction measurements. LiBF4 crystallizes as a merohedral twin in the trigonal space group P3(1)21 with a=4.892(5) A, c=11.002(12) A, V=228.0(4) A3, and Z=3 at 200 K. The twin is generated by a 2-fold rotation about the [10] direction. The lithium cation is coordinated by four fluorine atoms in a distorted tetrahedral manner, wherein two Li-F distances of 1.862(5) and 1.846(5) A are observed. The formula unit volume (FUV=V/Z) of 77.9 A3 for LiBF4 at 298 K is considerably larger than 72.7 A3 for NaBF4 and 72.5 A3 for AgBF4, despite the smaller size of Li+, indicating loose ionic packing of LiBF4. The thermodynamic evaluation of the decomposition temperature for LiBF4 was performed using the empirical relationship between the standard entropy and the FUV obtained. The results indicate that the large FUV of LiBF4 contributes to its higher decomposition temperature compared to that of LiPF6.

The `super acid' BF3H2O stabilized by 1,4-dioxane: new preparative aspects and the crystal structure of BF3H2O·C4H8O2

“…correction, the values of 1 agree well with those of the hydrates and those in almost undistorted BF 4 À as found in Li[BF 4 ] at 200 K [1.387 (3)-1.391 (3) Å ; Matsumoto et al, 2006] or in H 5 O 2 [BF 4 ] [1.381 (2)-1.399 (2) Å ; Mootz & Steffen, 1981a]. The bond-valence sum of B1 is as expected taking into account the 'uncorrected' nature of the r 0 values used (Brown & Altermatt, 1985).…”

Structural Interactions within Lithium Salt Solvates: Acyclic Carbonates and Esters

“…This same form of DMC···Li + cation coordination with disordered DMC solvent molecules was also present in a (DMC) 3/2 :LiDFOB solvate . The (DMC) 1/4 :LiBF 4 solvate contains BF 4 – anions coordinated to four Li + cations in a similar manner to what occurs in the pure LiBF 4 salt . Half of the Li + cations in this solvate have 4-fold coordination by four anions, as occurs in the structure for the pure salt (Figure ).…”

Li2B6O9F2, a New Acentric Fluorooxoborate

“…The distances d (B–O) are slightly shorter in trigonal planar coordination (1.327(3)–1.402(2) Å) than in tetrahedral coordination (1.421(2)–1.487(2) Å). Table 1 compiles all relevantB–O(F) angles and distances, which are in good agreement with reported data for borates9,16–21 and tetrafluoroborates 22,23. Each lithium atom is coordinated by one fluorine atom and three oxygen atoms, at distances varying from 1.8–2.2 Å (Figure 3, Table 2).…”