Hydrogen-bonding motifs in 4-carboxyphenylammonium nitrate and perchlorate monohydrate, and in bis(4-carboxyphenylammonium) sulfate.

In the title compounds, C7H8NO2+.NO3-, (I), C7H8NO2+.ClO4-.H2O, (II), and 2C7H8NO2+.SO4(2-), (III), the carboxyl planes of the 4-carboxyphenylammonium cations are twisted from the aromatic plane. A homonuclear C(8) hydrogen-bonding motif of 4-carboxyphenylammonium cations is observed in both (I) and (II), leading to ;head-to-tail' layers. The cations in (III) form carboxyl group dimers, making a graph-set motif of R2(2)(8). In all the structures, anions connect the cationic layers and an infinite chain running along the c axis is observed, having the C2(2)(6) graph-set motif. Interestingly, in (II), the anions are connected through weak hydrogen bonds involving the water molecules, leading to a graph-set motif of R4(4)(12). Alternate hydrophobic and hydrophilic layers are observed in all three compounds as a result of the column-like arrangement of the aromatic rings of the cations and the anions. Furthermore, in (I), head-to-tail N-H...O interactions and interactions linking the cations and anions form an R6(4)(16) hydrogen-bonding motif, resulting in a pseudo-inversion centre at (1/2, 1/2, 0).