Triphenyl[(triphenylphosphoranylidene)amino]phosphonium tetrakis(pentafluorophenyl)borate

In the title molecular salt, C36H30NP2 +·C24BF20 −, the P—N bond lengths in the cation are equal [1.573 (2) and 1.572 (2) Å], indicating a resonance structure and the P—N—P bond angle is 144.79 (12)°. In the crystal, weak C—H⋯F interactions link the cations and the anions.

In the title molecular salt, C 36 H 30 NP 2 + ÁC 24 BF 20 À , the P-N bond lengths in the cation are equal [1.573 (2) and 1.572 (2) Å ], indicating a resonance structure and the P-N-P bond angle is 144.79 (12) . In the crystal, weak C-HÁ Á ÁF interactions link the cations and the anions.
for this purpose (Luo et al. 2006, Fermín et al. 1999, Su et al. 2008a,b, Stephenson et al. 2005. Its CAS registry number is 227603-93-2. In the work of Luo and coworkers (Luo et al. 2006) this compound was used to study the fine structure of interface between two liquids using X-ray reflectivity of the interface. Vanýsek & Novák (2009) calculated the Gibbs energies of the transport for the individual ions between water and dichloroethane, the common organic phase for ITIES work. The structural information is important for understanding these Gibbs free energies.

Experimental
The preparation method is based on the metathesis of the starting materials with the elimination of water-soluble LiCl.
The framework of the procedure is described in (Fermín et al. 1999). The starting materials used were bis(triphenylphosphoranylidene)-ammonium chloride (Aldrich) and either lithium or potassium tetrakis(pentafluorophenyl)borate (Boulder Scientific Company). In later preparations potassium tetrakis(pentafluorophenyl)borate (also from Boulder Scientific Company) was used, with identical electrochemical results. Both starting materials were dissolved in a methanol:water 2:1 mixture, with a minimum of 10 ml per gram of starting materials used. The solutions were combined and the precipitate formed was rinsed in copious amounts of a methanol:water 2:1 mixture, followed by large amount of distilled water. The product was vacuum-filtered and dried. The recrystallization was done from hot acetone (Gobry 2001). The yield was 82%. It is possible to obtain higher yields, however, the intended use of the product is very sensitive to any impurity, and the product would deteriorate with higher recovery. Also, it was noted that the vacuum filtration needs to be done rapidly, as prolonged drying on the filter apparently contaminates the product with contaminants from the air, which are visible in the electrochemical work. The melting point of the carefully prepared product was 234-235°C.

Refinement
The hydrogen atoms on carbon atoms were refined using the riding model in SHELXL with the U iso equal to 1.5 times of that of the preceding carbon atoms for the methyl groups and 1.3 times for the rings. The C-H distances are equal to 0.97 and 0.96 Å for the CH 2 and CH 3 groups, respectively.

Figure 1
Thermal ellipsoid drawing of the title compound shown at the 50% probability level.

Special details
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.