Dimethylammonium perchlorate 18-crown-6 monohydrate clathrate

The reaction of dimethylamine, 18-crown-6, and perchloric acid in methanol yields the title compound, C2H8N+·ClO4 −·C12H24O6·H2O. The dimethylammonium cation and the water molecule interact with the 18-crown-6 unit: N—H⋯O hydrogen bonds are formed between the ammonium NH2 + group and four O atoms of the crown ether, while the water molecule on the other side of 18-crown-6 ring forms O—H⋯O hydrogen bonds with two other O atoms of the crown ether. All conventional donors and acceptors in the cations are thus engaged in hydrogen bonding. The ClO4 − anion is disordered over two sites, and occupancies for the disordered O atoms were fixed at 0.5. In the crystal, the cations and anions are arranged in alternating layers.

The reaction of dimethylamine, 18-crown-6, and perchloric acid in methanol yields the title compound, C 2 H 8 N + ÁClO 4 À Á-C 12 H 24 O 6 ÁH 2 O. The dimethylammonium cation and the water molecule interact with the 18-crown-6 unit: N-HÁ Á ÁO hydrogen bonds are formed between the ammonium NH 2 + group and four O atoms of the crown ether, while the water molecule on the other side of 18-crown-6 ring forms O-HÁ Á ÁO hydrogen bonds with two other O atoms of the crown ether. All conventional donors and acceptors in the cations are thus engaged in hydrogen bonding. The ClO 4 À anion is disordered over two sites, and occupancies for the disordered O atoms were fixed at 0.5. In the crystal, the cations and anions are arranged in alternating layers.

Comment
The crown ethers are of a great interest since their discovery by Pedersen (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 interactions, and if the host molecule has some specific sites, it is easy to realize high selectivity in ion or molecular recognition. 18-crown-6 has the highest affinity for ammonium cations RNH 3 + , and most studies of 18-crown-6 and its derivatives invariably showed the 1:1 stoichiometry with RNH 3 + cations.
The title compound dielectric permittivity was tested to systematically investigate the ferroelectric phase transitions of these materials (Fu et al., 2007;Ye et al., 2009;Zhang et al., 2009). The title compound has no dielectric anomalies, with the relative permittivity at 1 MHz being in the range 4-5 between 80 and 330 K (m.p. is 353 K), suggesting that no phase transition occurred within the measured temperature range.
The title compound is composed of cation [(CH 3 ) 2 NH 2 (18-Crown-6)] + , one isolated anion (ClO 4 ) -, and one lattice water molecule (Fig 1). The protonated dimethylamine [(CH 3 ) 2 NH 2 ] + and 18-crown-6 form a supramolecular structure  supplementary materials sup-2 Experimental Dimethylamine (2 mmol, 0.09 g) and an excess of perchloric acid (3 mmol, 0.302 g) were dissolved in methanol. 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 were obtained by slow evaporation of a methanol solution at room temperature over two days.

Refinement
All C-bonded H atoms were placed geometrically, with the C-H distances ranging from 0.96 to 0.97 Å. Isotropic displacement parameters were calculated as U iso (H) = 1.2U eq (C) for methylene groups and U iso (H) = 1.5U eq (C) for methyl groups. H atoms bonded to N and O atoms were found in a difference map and refined as riding atoms and with U iso (H) = 1.5U eq (carrier atom). O atoms for the perchlorate ion were splited over two sites, with equal occupancies fixed to 0.5.
Cl-O bond lengths were restrained, as well as displacement parameters for disordered O atoms (51 restraints).
Figures Fig. 1. The molecular structure of the title compound, with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and a single orientation for the disordered perchlorate anion is shown.