Crystal structures and hydrogen bonding in the anhydrous tryptaminium salts of the isomeric (2,4-di­chloro­phen­oxy)acetic and (3,5-di­chloro­phen­oxy)acetic acids

The anhydrous salts of 2-(1H-indol-3-yl)ethanamine (tryptamine) with isomeric (2,4-di­chloro­phen­oxy)acetic acid (2,4-D) and (3,5-di­chloro­phen­oxy)acetic (3,5-D), both C(10)H(13)N(2) (+)·C(8)H(5)Cl(2)O(3) (−) [(I) and (II), respectively], have been determined and their one-dimensional hydrogen-bonded polymeric structures are described. In the crystal of (I), the aminium H atoms are involved in three separate inter-species N—H⋯O hydrogen-bonding inter­actions, two with carboxyl­ate O-atom acceptors and the third in an asymmetric three-centre bidentate carboxyl­ate O,O′ chelate [graph set R (1) (2)(4)]. The indole H atom forms an N—H⋯O(carboxyl­ate) hydrogen bond, extending the chain structure along the b-axis direction. In (II), two of the three aminium H atoms are also involved in N—H⋯O(carboxyl­ate) hydrogen bonds similar to (I) but with the third, a three-centre asymmetric inter­action with carboxyl­ate and phen­oxy O atoms is found [graph set R (1) (2)(5)]. The chain polymeric extension is also along b. There are no π–π ring inter­actions in either of the structures. The aminium side-chain conformations differ significantly between the two structures, reflecting the conformational ambivalence of the tryptaminium cation, as found also in the benzoate salts.