3-Acetylanilinium bromide, nitrate and dihydrogen phosphate: hydrogen-bonding motifs in one, two and three dimensions.

In the title compounds, namely 3-acetylanilinium bromide, C(8)H(10)NO(+) x Br(-), (I), 3-acetylanilinium nitrate, C(8)H(10)NO(+) x NO(3)(-), (II), and 3-acetylanilinium dihydrogen phosphate, C(8)H(10)NO(+) x H(2)PO(4)(-), (III), each asymmetric unit contains a discrete cation, with a protonated amino group, and an anion. In the crystal structure of (I), the ions are connected via N-H...Br and N-H...O hydrogen bonds into a chain of spiro-fused R(2)(2)(14) and R(2)(4)(8) rings. In compound (II), the non-H atoms of the cation all lie on a mirror plane in the space group Pnma, while the nitrate ion lies across a mirror plane. The crystal structures of compounds (II) and (III) are characterized by hydrogen-bonded networks in two and three dimensions, respectively. The ions in (II) are connected via N-H...O hydrogen bonds, with three characteristic graph-set motifs, viz. C(2)(2)(6), R(2)(1)(4) and R(4)(6)(14). The ions in (III) are connected via N-H...O and O-H...O hydrogen bonds, with five characteristic graph-set motifs, viz. D, C(4), C(1)(2)(4), R(3)(3)(10) and R(4)(4)(12). The significance of this study lies in its illustration of the differences between the supramolecular aggregations in the bromide, nitrate and dihydrogen phosphate salts of a small organic molecule. The different geometry of the counter-ions and their different potential for hydrogen-bond formation result in markedly different hydrogen-bonding arrangements.