Solid-State Analysis of Monohydrated Halide Salts of Paracetamol

Three monohydrated halide salts of paracetamol: hydrochloride, hydrobromide, and hydroiodide were obtained and crystallized in order to compare their structures in the solid state. In all the investigated crystals, the ions and water molecules participate in O-H center dot center dot center dot O, N-H center dot center dot center dot X, and O-H center dot center dot center dot X (X = Cl-, Br- and I-) hydrogen bonds. This leads to the formation of multilayered structures stabilized by pi-pi interactions. In the case of the iodide salt, the presence of additional O-H center dot center dot center dot O interactions results in changes of the supramolecular synthons formed. The R-5(4)(13) and the R-4(6)(18) hydrogen bond motifs appear; the C center dot center dot center dot I contacts are also identified. The distance between neighboring layers increases with the increase of the size of the anion. An opposite trend is observed for the values of lattice energy, melting point temperature, and pK(a) of the respective hydrohalic acid.