N,N,2,4,6-Pentamethylanilinium hexafluorophosphate–1,4,7,10,13,16-hexaoxacyclooctadecane (2/1)

In the title compound, 2C11H18N+·2PF6 −·C12H24O6, the 18-crown-6 molecule has crystallographically imposed inversion symmetry. In the crystal, it interacts with the cation through weak C—H⋯O hydrogen bonds. The cations and anions are further linked via N—H⋯F and C—H⋯F hydrogen bonds, leading to a sandwich structure .

In the title compound, 2C 11 H 18 N + Á2PF 6 À ÁC 12 H 24 O 6 , the 18crown-6 molecule has crystallographically imposed inversion symmetry. In the crystal, it interacts with the cation through weak C-HÁ Á ÁO hydrogen bonds. The cations and anions are further linked via N-HÁ Á ÁF and C-HÁ Á ÁF hydrogen bonds, leading to a sandwich structure .
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: RZ5098).

Comment
As a continuation of our studies on the development of novel ferroelectric pure organic or inorganic compounds (Haertling et al., 1999;Homes et al., 2001), we investigated the physical properties of the title compound. Recently the crystal structure of the strictly related compound N,N,2,4,6-pentamethylanilinium hexafluorophosphate was reported by our group (Zhang, 2013). The dielectric constant of the title compound as a function of the temperature indicates that the permittivity is basically temperature-independent (dielectric constant equaling to 4.1 to 6.1), suggesting that this compound should be not a real ferroelectrics or there may be no distinct phase transition occurring within the measured temperature range. Similarly, below the melting point (180°C) of the compound, the dielectric constant as a function of temperature also goes smoothly, and there is no dielectric anomaly observed (dielectric constant equaling to 4.1 to 6.1).
Herein, we report the synthesis and crystal structure of the title compound.
Dipole-dipole and van der Waals interactions are effective in stabilizing the molecular packing.

Refinement
H atoms were positioned geometrically and refined using a riding model, with C-H = 0.97 Å, N-H = 0.91 Å, and U iso (H) = 1.2 U eq (C, N) or 1.5 U eq (C) for methyl H atoms

Figure 2
Crystal packing of the title compound viewed along the b axis, showing the hydrogen bonding network (dashed lines).

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.