Crystal structure and Hirshfeld surface analysis of 1-carb­­oxy-2-(3,4-di­hy­droxy­phen­yl)ethan-1-aminium chloride 2-ammonio-3-(3,4-di­hy­droxy­phen­yl)propano­ate: a new polymorph of L-dopa HCl and isotypic with its bromide counterpart

The title mol­ecular salt, C9H12NO4+·Cl−·C9H11NO4, is isotypic with that of the bromide counterpart [Kathiravan et al. (2016[Kathiravan, P., Balakrishnan, T., Venkatesan, P., Ramamurthi, K., Percino, M. J. & Thamotharan, S. (2016). Acta Cryst. E72, 1544-1548.]). Acta Cryst. E72, 1544–1548]. The title salt is a second monoclinic polymorph of the L-dopa HCl structure reported earlier in the monoclinic space group P21 [Jandacek & Earle (1971[Jandacek, R. J. & Earle, K. M. (1971). Acta Cryst. B27, 841-845.]). Acta Cryst. B27, 841–845; Mostad & Rømming (1974[Mostad, A. & Rømming, C. (1974). Acta Chem. Scand. B28, 1161-1168.]). Acta Chemica Scand. B28, 1161–1168]. In the title compound, monoclinic space group I2, one of the dopa mol­ecules has a positive charge with a protonated α-amino group and the α-carb­oxy­lic acid group uncharged, while the second dopa mol­ecule has a neutral charge, the α-amino group is protonated and the α-carb­oxy­lic acid is deprotonated. In the previously reported form, a single dopa mol­ecule is observed in which the α-amino group is protonated and the α-carb­oxy­lic acid group is uncharged. The invariant and variations of various types of inter­molecular inter­actions present in these two forms of dopa HCl structures are discussed with the aid of two-dimensional fingerprint plots.