4-[(2′-Cyanobiphenyl-4-yl)methyl]morpholin-4-ium hexafluoridophosphate

In the cation of the title compound, C18H19N2O+·PF6 −, the morpholine ring adopts the usual chair conformation and the dihedral angle between the benzene rings is 67.55 (11)°. The F atoms of the anion are disordered over two orientations with a refined occupancy ratio of 0.65 (2):0.35 (2). In the crystal, intermolecular N—H⋯N hydrogen bonds link the cations into chains parallel to the c axis. The crystal packing is further enforced by interionic C—H⋯F hydrogen bonds.

In the cation of the title compound, C 18 H 19 N 2 O + ÁPF 6 À , the morpholine ring adopts the usual chair conformation and the dihedral angle between the benzene rings is 67.55 (11) . The F atoms of the anion are disordered over two orientations with a refined occupancy ratio of 0.65 (2):0.35 (2). In the crystal, intermolecular N-HÁ Á ÁN hydrogen bonds link the cations into chains parallel to the c axis. The crystal packing is further enforced by interionic C-HÁ Á ÁF hydrogen bonds.

Comment
The title compound was prepared as part of our ongoing studies of hydrogen-bonding interactions in the crystal structure of protonated amines. The importance of molecular salts in pharmaceutical formulations is well known. For a given active ingredient, the isolation and selection of a salt with the appropriate physicochemical properties involves significant screening activity, as discussed at some length in the literature (Tong & Whitesell, 1998;Shanker, 1994). Here we report the synthesis and crystal structure of the title compound, 4-[(2′-cyanobiphenyl-4-yl)methyl]morpholin-4-ium hexafluorophosphate.
In the title compound ( Fig. 1), bond distances and angles agree very well with those reported for a closely related nitrate (SiMa, 2010) and tetrafluoridoborate (Li et al., 2011) derivatives. In the cation, the morpholine ring adopts the usual chair conformation, and the dihedral angle formed by the phenyl rings is 67.55 (11)°. The hexafluorophosphate anion displays a distorted octahedral geometry, the fluorine atoms being disordered over two orientations with site occupancies of 0.65 (2) and 0.35 (2) for the major and minor components of disorder, respectively. In the structure, the cations interact through intermolecular N-H···N hydrogen bonds (Table 1) to form chains parallel to the c axis ( Fig. 2). Crystal packing is further consolidated by interionic C-H···O hydrogen bonds.

Experimental
To a stirred solution of 4′-(morpholinomethyl)biphenyl-2-carbonitrile (5.56 g, 0.02 mol) in methanol (30 mL), hexafluorophosphoric acid (4.17 g, 0.02 mol) was added at the room temperature. The precipitate was filtered and washed with a small amount of ethanol 95%. Single crystals suitable for X-ray diffraction analysis were obtained from slow evaporation of a solution of the title compound in water at room temperature.

Refinement
All H-atoms were positioned geometrically and refined using a riding model, with N-H = 0.91 Å, C-H = 0.93-0.96 Å and U iso (H) = 1.2 U eq (N, C). The fluorine atoms of the anion are disoreder over two orientations with a refined occupancy ratio of 0.65 (2):0.35 (2).  The molecular structure of the title compound, showing displacement ellipsoids drawn at the 30% 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.