Crystal structures and hydrogen bonding in the morpholinium salts of four phen­oxy­acetic acid analogues

The anhydrous salts morpholinium (tetra­hydro-2-H-1,4-oxazin-4-ium) phen­oxy­acetate, C(4)H(10)NO(+)·C(8)H(7)O(3) (−), (I), morpholinium (4-fluoro­phen­oxy)acetate, C(4)H(10)NO(+)·C(8)H(6 )FO(3) (−), (II), and isomeric morpholinium (3,5-di­chloro­phen­oxy)acetate (3,5-D), (III), and morpholinium (2,4-di­chloro­phen­oxy)acetic acid (2,4-D), C(4)H(10)NO(+)·C(8)H(5)Cl(2)O(3) (−), (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 inter­action with the two carboxyl O-atom acceptors of the anion. With the structure of (II), the primary N—H⋯O inter­action is linear. In the structures of (I), (II) and (III), the second N—H⋯O(carbox­yl) 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 hetero­tetra­meric structure.