4-Methylanilinium tetrafluoroborate 18-crown-6 clathrate

In the title compound, C7H10N+·BF4 −·C12H24O6, the protonated 4-methylanilinium cation interacts with 18-crown-6 forming a rotator–stator structure, (C6H4CH3NH3 +)(18-crown-6), through three bifurcated N—H⋯(O,O) hydrogen bonds between the ammonium groups of the cations (–NH3) and the O atoms of the crown ether molecule. The BF4 − anions, the methyl group and the protonated –NH3 groups of the 4-methylanilinium lie on a dual axis of rotation. The 18-crown-6 unit is perpendicular to the dual axis of rotation and the mirror plane which contains the dual axis of rotation. The benzene ring of 4-methylanilinium is perpendicular to the mirror plane and parallel to the dual axis.

In the title compound, C 7 H 10 N + ÁBF 4 À ÁC 12 H 24 O 6 , the protonated 4-methylanilinium cation interacts with 18-crown-6 forming a rotator-stator structure, (C 6 H 4 CH 3 NH 3 + )(18crown-6), through three bifurcated N-HÁ Á Á(O,O) hydrogen bonds between the ammonium groups of the cations (-NH 3 ) and the O atoms of the crown ether molecule. The BF 4 À anions, the methyl group and the protonated -NH 3 groups of the 4-methylanilinium lie on a dual axis of rotation. The 18crown-6 unit is perpendicular to the dual axis of rotation and the mirror plane which contains the dual axis of rotation. The benzene ring of 4-methylanilinium is perpendicular to the mirror plane and parallel to the dual axis.

Comment
The crown ethers were of a great interest since their discovery had been reported by Pedersen (Pedersen et al. 1967).
The ability of these macrocycles to form non-covalent,H-bonding complexes with ammonium cations has been actively investigated. Both the size of the crown ether and the nature of the ammonium cation (-NH 4 + , RNH 3 + , etc) can influence on the stoichiometry and stability of these host-guest complexes. The host molecules combine with the guest species by intermolecular interaction, and if the host molecule possess some specific sites, it is easy to realise high selectivity in ion or molecular recognitions.18-crown-6 have the highest affinity for ammonium cation RNH 3 + , while most studies of 18-crown-6 and its derivatives invariably showed a 1:1 stoichiometry with RNH 3 + cations.
The title compound dielectric permittivity is tested to systematically investigate the ferroelectric phase transitions materials (Fu et al. 2007;Ye et al. 2009;Zhang et al. 2009). The title compound have no dielectric anomalies with the value of 4-5 and 6-8 under 1M Hz in the temperature from 80 to 300 K and 300 to 473 K (the compound m.p.> 473 K), respectively, suggesting that the compound should be no distinct phase transition occurred within the measured temperature range.
Then 18-crown-6 (2 mmol, 0.528 g) was added to the mixture. The precipitate was filtered and washed with a small amount of methanol. Single crystals suitable for X-ray diffraction analysis were obtained from slow evaporation of methanol solution at room temperature after two days.
supplementary materials sup-2 Refinement All the C-H hydrogen atoms were calculated geometrically and with C-H distances ranging from 0.93 to 0.97 Å and were allowed to ride on the C and O atoms to which they are bonded. With which U iso (H) = 1.2Ueq(C).
Figures Fig. 1. The molecular structure of the title compound, with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 Rfactors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (