Poly[[(acetonitrile)lithium(I)]-μ3-tetrafluoridoborato]

The structure of the title compound, [Li(BF4)(CH3CN)]n, consists of a layered arrangement parallel to (100) in which the Li+ cations are coordinated by three F atoms from three tetrafluoridoborate (BF4 −) anions and an N atom from an acetonitrile molecule. The BF4 − anion is coordinated to three different Li+ cations though three F atoms. The structure can be described as being built from vertex-shared BF4 and LiF3(NCCH3) tetrahedra. These tetrahedra reside around a crystallographic inversion center and form 8-membered rings.

The structure of the title compound, [Li(BF 4 )(CH 3 CN)] n , consists of a layered arrangement parallel to (100) in which the Li + cations are coordinated by three F atoms from three tetrafluoridoborate (BF 4 À ) anions and an N atom from an acetonitrile molecule. The BF 4 À anion is coordinated to three different Li + cations though three F atoms. The structure can be described as being built from vertex-shared BF 4 and LiF 3 (NCCH 3 ) tetrahedra. These tetrahedra reside around a crystallographic inversion center and form 8-membered rings.

Poly[[(acetonitrile)lithium(I)]-3 -tetrafluoridoborato]
D. M. Seo, P. D. Boyle and W. A. Henderson Comment In this structure, atoms F1 and F2 are endocyclic linking the boron atom to the lithium atom while F3 and F4 are exocyclic.
Neighboring rings are linked through a Li1-F3 bond to form an infinite two dimensional network which orients parallel to (1 0 0). The interface between the two dimensional networks is occupied by the aliphatic ends of the acetonitrile molecules and the F4 atoms and is largely at van der Waal contact distances. There is, however, a close intermolecular contact of 3.1601 (11) Å between the nitrile carbon atom, C1, and F4 (1 -x, 1 -y, 2 -z).
Solvate structures provide significant insight into the species which may exist in electrolytes solutions. Solvates based upon acetonitrile and lithium salts are particularly noteworthy as dinitrile solvents gain increasing interest as high-voltage solvents for lithium battery electrolytes. The phase diagram for (CH 3 CN) n -LiBF 4 mixtures indicates that at least three different solvates may form with 4/1 (T m = -12°C), 2/1 (T m = 25°C) and 1/1 (T m = 63°C) AN/Li compositions. The 4/1 solvate may resemble that for LiClO 4 in which the Li + cations are fully solvated by four acetonitrile molecules and the anions are uncoordinated. The 2/1 solvate, in turn, may resemble that for LiBr in which the Li + cations are solvated by two acetonitrile molecules and two anions to form aggregated dimer solvates. The 1/1 solvate structure is reported here.

Experimental
LiBF 4 (99.998%) was purchased from Sigma-Aldrich and used as-received. Anhydrous acetonitrile (Sigma Aldrich, 99.8%) was used as-received. In a Vacuum Atmospheres inert atmosphere (N 2 ) glove box (< 5 p.p.m. H 2 O), LiBF 4 (1 mmol) and acetonitrile (1.5 mmol) were sealed in a vial and the mixture heated on a hot plate to form a homogeneous solution. Upon standing at ambient temperature, colorless plate single crystals suitable for analysis formed.

Refinement
The structure was solved by direct methods using the XS program. All non-hydrogen atoms were obtained from the initial solution. The hydrogen atoms were introduced at idealized positions and were allowed to refine isotropically. The structural model was fit to the data using full matrix least-squares based on F 2 . The calculated structure factors included corrections for anomalous dispersion from the usual tabulation. The structure was refined using the XL program from SHELXTL, and graphic plots were produced using the ORTEP-3 program.