Two-dimensional hydrogen-bonded polymers in the crystal structures of the ammonium salts of phen­oxy­acetic acid (4-fluoro­phen­oxy)acetic acid and (4-chloro-2-methyl­phen­oxy)acetic acid

摘要

The structures of the ammonium salts of phen­oxy­acetic acid, NH4 ⁺·C8H6O3 ⁻, (I), (4-fluoro­phen­oxy)acetic acid, NH4 ⁺·C8H5FO3 ⁻, (II), and the herbicidally active (4-chloro-2-methyl­phen­oxy)acetic acid (MCPA), NH4 ⁺·C9H8ClO3 ⁻·0.5H2O, (III) have been determined. All have two-dimensional layered structures based on inter-species ammonium N—H⋯O hydrogen-bonding associations, which give core substructures consisting primarily of conjoined cyclic motifs. The crystals of (I) and (II) are isomorphous with the core comprising R 1 ²(5), R 1 ²(4) and centrosymmetric R 4 ²(8) ring motifs, giving two-dimensional layers lying parallel to (100). In (III), the water mol­ecule of solvation lies on a crystallographic twofold rotation axis and bridges two carboxyl O atoms in an R ₄ ⁴(12) hydrogen-bonded motif, creating two R ₄ ³(10) rings, which together with a conjoined centrosymmetric R₄²(8) ring incorporating both ammonium cations, generate two-dimensional layers lying parallel to (100). No π–π ring associations are present in any of the structures.