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

Abstract

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 C10H13N2+·C8H5Cl2O3−[(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 carboxylateO,O′chelate [graph setR12(4)]. The indole H atom forms an N—H...Ocarboxylatehydrogen bond, extending the chain structure along theb-axis direction. In (II), two of the three aminium H atoms are also involved in N—H...Ocarboxylatehydrogen bonds similar to (I) but with the third, a three-centre asymmetric interaction with carboxylate and phenoxy O atoms is found [graph setR12(5)]. The chain polymeric extension is also alongb. 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.