Hydrogen bonding in the bromide salts of 4-aminobenzoic acid and 4-aminoacetophenone.

In the title compounds, 4-carboxyanilinium bromide, C(7)H(8)NO(2)(+) x Br(-), (I), and 4-acetylanilinium bromide, C(8)H(10)NO(+) x Br(-), (II), each asymmetric unit contains a discrete cation with a protonated amino group and a halide anion. Both crystal structures are characterized by two-dimensional hydrogen-bonded networks. The ions in (I) are connected via N-H...Br, N-H...O and O-H...Br hydrogen bonds, with three characteristic graph-set motifs, viz. C(8), C(2)(1)(4) and R(3)(2)(8). The centrosymmetric hydrogen-bonded R(2)(2)(8) dimer motif characteristic of carboxylic acids is absent. The ions in (II) are connected via N-H...Br and N-H...O hydrogen bonds, with two characteristic graph-set motifs, viz. C(8) and R(4)(2)(8). The significance of this study lies in its illustration of the differences between the supramolecular aggregations in two similar compounds. The presence of the methyl group in (II) at the site corresponding to the hydroxyl group in (I) results in a significantly different hydrogen-bonding arrangement.