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, C(8)H(12)NO(2) (+)·C(7)H(5)O(2) (−), I, dopamine 4-nitro­benzoate, C(8)H(12)NO(2) (+)·C(7)H(4)NO(4) (−), II, dopamine ethane­di­sul­fon­ate, 2C(8)H(12)NO(2) (+)·C(2)H(4)O(6)S(2) (2−), III, and dopamine 4-hy­droxy­benzene­sul­fon­ate monohydrate, C(8)H(12)NO(2) (+)·C(6)H(5)O(4)S(−)·H(2)O, 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.