Abstract: | Both the 1:1 and 2:1 molecular adducts of 4‐methylimidazole (4‐MeIm) and terephthalic acid (H2TPA) are organic salts, viz. C4H7N2+·C8H5O4?, (I), and 2C4H7N2+·C8H4O42?, (II), respectively. The component ions in (I) are linked by N—H...O and O—H...O hydrogen bonds into continuous two‐dimensional layers built from R64(32) hydrogen‐bond motifs running parallel to the (100) plane. These adjacent two‐dimensional layers are in turn linked by a combination of C—H...O, C—H...π and π–π interactions into a three‐dimensional network. In the crystal structure of (II), with the anion located on an inversion centre, only N—H...O hydrogen bonds result in two‐dimensional layers built from R88(42) hydrogen‐bond motifs running parallel to the (102) plane. Being similar to those in (I), these layers are also linked by means of C—H...O, C—H...π and π–π interactions, forming a three‐dimensional network. This study indicates that, on occasion, a change of the reactant concentration can exert a pivotal influence on the construction of supramolecular structures based on hydrogen bonds. |