Propane-1,3-diaminium bis(tetrafluoroborate)–18-crown-6 (1/2)

In the title compound, C3H12N2 2+·2BF4 −·2C12H24O6, the central C atom of the propane-1,3-diammonium cation lies on a crystallographic twofold rotation axis. The terminal NH3 + groups insert into the crown rings through strong N—H⋯O hydrogen-bonding interactions, resulting in the formation of a 1:2 supramolecular [(C3H12N2)·(C12H24O6)2]2+ complex. The anions are linked to the supramolecular complexes via weak C—H⋯F hydrogen bonds. The F atoms of the anion are disordered over two orientations with site occupancies of 0.5.

In the title compound, C 3 H 12 N 2 2+ Á2BF 4 À Á2C 12 H 24 O 6 , the central C atom of the propane-1,3-diammonium cation lies on a crystallographic twofold rotation axis. The terminal NH 3 + groups insert into the crown rings through strong N-HÁ Á ÁO hydrogen-bonding interactions, resulting in the formation of a 1:2 supramolecular [(C 3 H 12 N 2 )Á(C 12 H 24 O 6 ) 2 ] 2+ complex. The anions are linked to the supramolecular complexes via weak C-HÁ Á ÁF hydrogen bonds. The F atoms of the anion are disordered over two orientations with site occupancies of 0.5.
The dielectric constant of the title compound as a function of temperature indicates that the permittivity is basically temperature-independent, suggesting that this compound should be not a real ferroelectrics or there may be no distinct phase transition occurred within the measured temperature range. Similarly, below the melting point (412 K) of the compound, the dielectric constant as a function of temperature also goes smoothly, and there is no dielectric anomaly observed (dielectric constant ranging from 4.5 to 8.8).

Refinement
All H atoms attached to C atoms were fixed geometrically and treated as riding with 0.97 Å and U iso (H) = 1.2U eq (C). The positional parameters of the N-bound H atoms were intially refined freely, subsequently they were restrained using a N-H distance of 0.89 (2) Å, and in the final refinements treated as riding with U iso (H) = 1.5U eq (N). All F atoms were disordered over two sites with occupancies of 0.5, and were refined anisotropically using ADP restraints (SIMU and DELU).

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 > 2sigma(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.

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