Sodium pentafluorophenylborate

The crystal structure of the title compound, Na[(C6F5)BH3], is composed of discrete anions and cations. The sodium cations are surrounded by four anions with three short Na⋯B [2.848 (8), 2.842 (7) and 2.868 (8) Å] and two short Na⋯F contacts [2.348 (5) and 2.392 (5) Å], forming a three-dimensional network. The anion is the first structural example of a pentafluorophenyl ring carrying a BH3 group.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: NG5300). The hydridoborates [(C 6 F 5 )BH 3 ]and [(C 6 F 5 ) 2 BH 2 ]are convenient starting materials for the in situ generation of the boranes (C 6 F 5 )BH 2 and (C 6 F 5 ) 2 BH (Schnurr et al., 2011). In this paper we report the crystal structure of Na[(C 6 F 5 )BH 3 ] which was obtained from the reaction mixture of (C 6 F 5 )B(OMe) 2 and Li[AlH 4 ] by a cation exchange with NaOH (Fig. 1).
It is remarkable that this is the first structure with an pentafluorophenyl ring carrying a BH 3 group. A search in the Cambridge Crystallographic Database (CSD, Version 5.33 of November 2011, plus three updates (Allen, (2002). Acta Cryst. B58, 380-388) yielded no hit at all for this fragment.

Experimental
In a round bottom flask (C 6 F 5 )B(OMe) 2 (0.16 g, 0.65 mmol) was dissolved in 10 ml diethyl ether. Under stirring a 1 m solution of Li[AlH 4 ] in diethyl ether (1.2 mmol, 1.1 ml) was added via canula. A brown slurry was obtained which was treated with 3 ml aqueous NaOH (3 mmol) and 15 ml benzene. Insoluble material was removed by filtration from the organic layer. Single crystals of the title compound were obtained of the concentrated benzene solution (5 ml). Yield 20%.

Refinement
Due to the absence of anomalous scatterers, the absolute structure could not be determined and 414 Friedel pairs were merged. H atoms were located in a difference map, but geometrically positioned and refined using a riding model with fixed individual displacement parameters [U(H) = 1.5 U eq (B)] and with B-H = 0.98 Å. The BH 3 group was allowed to rotate but not to tip. SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008  Reaction scheme for obtaining the title compound.

Figure 2
Perspective view of the title compound. Displacement ellipsoids are drawn at the 30% probability level.  Environment of a sodium cation. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.37 e Å −3 Δρ min = −0.45 e Å −3 Special details Experimental. ; Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.