Crystal structure and Hirshfeld surface analysis of 1-carboxy-2-(3,4-dihydroxyphenyl)ethan-1-aminium bromide 2-ammonio-3-(3,4-dihydroxyphenyl)propanoate

In the title molecular salt, C9H12NO4+-Br-center dot C9H11NO4, one of the dopa molecules is in the cationic form in which the a-amino group is protonated and the a-carboxylic acid group is uncharged, while the second dopa molecule is in the zwitterion form. The Br- anion occupies a special position and is located on a twofold rotation axis. The two dopa molecules are interconnected by short O-H center dot center dot center dot O hydrogen bonds. In the crystal, the various units are linked by O-H center dot center dot center dot O, N-H center dot center dot center dot Br and N-H center dot center dot center dot O hydrogen bonds, forming a three-dimensional framework. The title compound was refined as an inversion twin with an absolute structure parameter of 0.023 (8).