Crystal structures and hydrogen bonding in the morpholinium salts of four phen-oxy-acetic acid analogues

The anhydrous salts morpholinium (tetra-hydro-2-H-1,4-oxazin-4-ium) phen-oxy-acetate, C4H10NO(+)·C8H7O3 (-), (I), morpholinium (4-fluoro-phen-oxy)acetate, C4H10NO(+)·C8H6 FO3 (-), (II), and isomeric morpholinium (3,5-di-chloro-phen-oxy)acetate (3,5-D), (III), and morpholinium (2,4-di-chloro-phen-oxy)acetic acid (2,4-D), C4H10NO(+)·C8H5Cl2O3 (-), (IV), have been determined and their hydrogen-bonded structures are described. In the crystals of (I), (III) and (IV), one of the the aminium H atoms is involved in a three-centre asymmetric cation-anion N-H⋯O,O' R 1 (2)(4) hydrogen-bonding inter-action with the two carboxyl O-atom acceptors of the anion. With the structure of (II), the primary N-H⋯O inter-action is linear. In the structures of (I), (II) and (III), the second N-H⋯Ocarbox-yl hydrogen bond generates one-dimensional chain structures extending in all cases along [100]. With (IV), the ion pairs are linked though inversion-related N-H⋯O hydrogen bonds [graph set R 4 (2)(8)], giving a cyclic hetero-tetra-meric structure.