SYNTHESIS OF SALTS OF THE HYDROGEN DICHLORIDE ANION IN AROMATIC SOLVENTS .2. SYNTHESES AND CRYSTAL-STRUCTURES OF [K.18-CROWN-6][CL-H-CL], [MG.18-CROWN-6][CL-H-CL]2, [H3O.18-CROWN-6][CL-H-CL], AND THE RELATED [H3O.18-CROWN-6][BR-H-BR]

The reaction of HCl(g), H2O, and 18-crown-6 in toluene gives [H3O·18-crown-6][Cl—H—Cl]·3.6tol (tol = toluene), from which crystals of [H3O·18-crown-6] [Cl—H—Cl] are isolated: space group P21/c; a = 10.475 (7), b = 20.767 (9), c = 8.583 (7) Å; 0 = 96.23 (3)°; Z = 4 for Dc= 1.28 g cm−3; R = 0.042 for 493 independent observed reflections. The liquid clathrate [H3OÅ18-crown-6][Cl—H—Cl]·3.6tol dissolves KC1, and upon standing, the solution affords crystals of [K·18-crown-6][Cl—H—Cl]: space group P21/c; a = 8.325 (2), b = 14.094 (4), c = 7.893 (6) Å; β = 98.56 (4)°; Z = 2 for Dc= 1.37 g cm−3; R = 0.055 for 1194 independent observed reflections. In a similar fashion, the liquid clathrate dissolves MgCl2and yields [Mg·18-crown-6][Cl—H—Cl]2: space group Pbca; a = 18.310 (7), b = 7.512 (6), c = 29.085 (8) Å; Z = 8 for Dc= 1.44 g cm−3; R = 0.066 for 1204 observed reflections. The [Br—H—Br]−anion is produced by the reaction of HBr(g), H2O, and 18-crown-6 in toluene. [H3O·18-crown-6][Br—H—Br] is isomorphous with the [Cl—H—Cl]−analogue, and the crystals belong to space group P21/c with a = 10.588 (1) Å, b = 21.060 (2) Å, c = 8.753 (1) Å, β = 95.25 (4)°, and Dc= 1.52 g cm−3for Z = 4; R = 0.059 for 1697 observed reflections. The Cl…Cl separations range from 3.11 (1) Å in the H3O+salt to 3.331 (2) Å in the Mg2+analogue. The angle at the hydrogen atom in the hydrogen dichloride ranges from 161° for the [Mg-18-crown-6]2+salt to 180° for the [K·18-crown-6]+salt. The short CI…Cl separations in the H3O+and K+salts are attributed to the absence of a strong directional interaction of the anion with the cation. For the long Cl…Cl in the Mg2+case, the magnesium atom is bonded to one of the chlorine atoms at 2.428 (6) and 2.454 (3) Å (two independent anions). The Br…Br distance in [H3O+·18-crown-6] [Br-H-Br] is 3.377 (1) Å. © 1990, American Chemical Society. All rights reserved.