Structure of the 18-crown-6 complex with ammonium hexafluorosilicate and water

The crystalline host-guest type complex [(18-crown-6 . NH4)(2)][SiF6]. 4H(2)O has been obtained as the result of the interaction of SiF4. 2NH(3) with 18-crown-6 (18C6) in an aqueous medium. Crystal data: monoclinic, space group C2/c, a = 26.541(2), b = 8.363(2), c = 20.469(2) Angstrom, beta = 122.43(1)degrees and Z = 4. The final R-value is 0.070 for 3253 reflections with I greater than or equal to 2 sigma (I). The crystals consist of the complex [NH4. 18C6](+) cations, [SiF6](2-) anions and water molecules. The ammonium cation is hydrogen bonded by three of its H-atoms to the crown ether oxygen atoms with N(1). . .O separations 2.923(5)-2.940(5) Angstrom and by the fourth H-atom to the fluorine atom of the hexafluorosilicate anion, the N(1). . .F(4) distance being 2.797(6) Angstrom. The conformation of the macrocycle and the hydrogen-bond geometry in the complex cation closely resemble those in related adducts between 18-crown-6 and ammonium salts. All crystal components are connected via a system of hydrogen bonds into a ribbon along the b axis in the unit cell.