Structure of the Molecular Complexes of 18-Crown-6 with 1,2,5-Oxadiazole Derivatives

Abstract

This paper reports on an X-ray diffraction analysis of host–guest type molecular complexes of 18-crown-6 with 1,2,5-oxadiazole derivatives: ethyl 4-amino-1,2,5-oxadiazole-3-carboxylic ether (1:1) (complex I), 4-(2-chloroethylamino)-1,2,5-oxadiazole-3-carboxylic acid hydrazide (1:2) (complex II), and 4-amino-1,2,5-oxadiazole-3-carboxylic acid amide monohydrate (1:1:1) (complex III). Crystals I are monoclinic with cell parameters a = 8.960(2), b = 18.118(4), c = 14.405(3) Å, β = 106.9(3)°, space group P2₁/n, R = 0.054 for 4082 reflections. The 18-crown-6 and guest molecules are linked by hydrogen bonds of NH⋯O(crown) and CH⋯O(crown) types based on the “head-to-tail” principle, alternating in infinite chains along the y axis in the crystal. Crystals II are triclinic with cell parameters a = 8.615(2), b = 9.249(2), c = 10.987(2) Å, α = 106.86(3), β = 95.25(3), γ = 97.74(3)°, space group P1, R = 0.046 for 3006 reflections. The guest molecules are united into dimers by N–H⋯O=C hydrogen bonds. The 18-crown-6 molecules and the dimer associates of the guest form chains along [110] in the crystal. Crystals III are monoclinic with cell dimensions a = 13.238(3), b = 19.004(4), c = 8.485(2) Å, β = 100.75(3)°, space group Cc, R = 0.051 for 2032 reflections. The crown ether molecule is disordered over two positions. The NH⋯O=C and NH⋯N type hydrogen bonds link the guest molecules into chains. The water molecules serve to bridge the chains with crown ether molecules, forming ribbons whose axis lies along the z direction in the crystal.