A structural comparison of salt forms of dopamine with the structures of other phenylethylamines

The structures of four salt forms of dopamine are reported. These are dopamine [2-(3,4-dihydroxyphenyl)ethan-1-aminium] benzoate, C₈H₁₂NO₂⁺·C₇H₅O₂^-, I, dopamine 4-nitrobenzoate, C₈H₁₂NO₂⁺·C₇H₄NO₄^-, II, dopamine ethanedisulfonate, 2C₈H₁₂NO₂⁺·C₂H₄O₆S₂^2-, III, and dopamine 4-hydroxybenzenesulfonate monohydrate, C₈H₁₂NO₂⁺·C₆H₅O₄S^-·H₂O, IV. In all four structures, the dopamine cation adopts an extended conformation. Intermolecular interaction motifs that are common in the salt forms of tyramine can be found in related dopamine structures, but hydrogen bonding in the dopamine structures appear to be more variable and less predictable than for tyramine. Packing analysis discovered three dopamine-containing groups of structures that can be described as isostructural with regards to the cation positions. Two of these groups contain both dopamine and tyramine species, and one of these is also highly variable in other ways too, containing anhydrous and hydrated forms, different anion types and ionized and neutral phenylethylamine species. As such, the group illustrates that packing behaviour can be robust and similar even where intermolecular interactions such as hydrogen bonds are very different.