Ammonium hexafluoridophosphate–18-crown-6 (1/1)

In the crystal structure of the title compound, NH4 +·PF6 −·C12H24O6, the cation is situated in the 18-crown-6 ring, forming a supramolecular rotator-stator-like structure held by N—H⋯O hydrogen bonds. The six O atoms of the crown ether lie approximately in a plane [mean deviation 0.2129 (3) Å]; the N atom is displaced by 0.864 (3)Å from the centroid of the 18-crown-6 ring. The slightly distorted tetrahedral cations further interact with the slightly distorted octahedral anions via intermolecular N—H⋯F hydrogen bonds.

In the crystal structure of the title compound, NH 4 + ÁPF 6 À Á-C 12 H 24 O 6 , the cation is situated in the 18-crown-6 ring, forming a supramolecular rotator-stator-like structure held by N-HÁ Á ÁO hydrogen bonds. The six O atoms of the crown ether lie approximately in a plane [mean deviation 0.2129 (3) Å ]; the N atom is displaced by 0.864 (3)Å from the centroid of the 18-crown-6 ring. The slightly distorted tetrahedral cations further interact with the slightly distorted octahedral anions via intermolecular N-HÁ Á ÁF hydrogen bonds.

Related literature
For background to 18-crown-6 compounds, see: Bajaj & Poonia (1988);Fender et al. (2002); Kryatova et al. (2004). For related structures. see: Dapporto et al. (1996); Pears et al.  Table 1 Hydrogen-bond geometry (Å , ). the nature of the ammonium cation (NH 4 + ,RNH 3 + , R 2 NH 2 + , etc.) and the size of the crown ether can work on the stability and stoichiometry of these host-guest complexes. The host molecules combine with the guest species by intermolecular interaction, 18-Crown-6 has a high affinity for RNH 3 + cations and most studies of 18-crown-6 and its derivatives invariably showed a 1:1 stoichiometry with RNH 3 + cations. For similar structures, see: Dapporto et al., 1996;Pears et al., 1988. In our laboratory, the title compound has been synthesized and its crystal structure is herein reported.
The title compound crystallizes in the P2 1 /n space group with an asymmetric unit consisting of a cationic [(NH 4 )(18crown-6)] + moiety and an isolated anionic PF 6 - (Fig 1). The NH 4 + nests in the 18-crown-6 ring to form a superamolecular rotator-stator-like structure by intramolecular N-H···O hydrogen-bonded interactions between the NH 4 + (H1C, H1D and H1F)and the six oxygen atoms of the crown ether (Fig 2). Intramolecular N-H···O hydrogen distances fall within the normal range: 2.871 (3) and 3.018 (3) Å (Table 1). The six oxygen atoms of the crown ether lie approximately in a plane with the mean deviation of 0.2129 Å, the N atom aparts from the center of the crown ring about 0.864 Å. The slightly distorted tetrahedralcations NH 4 + further interact with F1 i and F3 i (symmetry code, i: 1 -x, 1 -y, -z) of the slightly distorted octahedral anions PF 6 -(The P-F bond lengths are within the range of 1.51 -1.60 Å, the F-P-F bond angles are within the range of 87.78 -92.48°) by intermolecular N-H···F hydrogen bonds (Table 1 and Fig 2).

Experimental
In room temperature 18-crown-6 (4 mmol, 1.05 g) were dissolved in 50 ml me thanol, after addition of excess hexafluorophosphoric acid to afford a white microcrystallic precipitation for H 3 O + ?PF 6 -(18-crown-6) (about 95% yield). Then dissolve the precipitation again in 50 ml water and addition of excess concentrated ammonia to afford the solution without any participation under stirring at the ambient temperature. Block colorless single crystals suitable for X-ray structure analysis were obtained by the slow evaporation of the above solution after a week in air.
The dielectric constant of the compound as a function of temperature indicates that the permittivity is basically temperature-independent (ε = C/(T-T 0 )), suggesting that this compound is not ferroelectric or there may be no distinct phase transition occurring within the measured temperature range between 93 K and433 K (below the compound melting point 463 K).