2-Amino-5-bromo­pyridinium 5-chloro-2-hy­droxy­benzoate

In the 5-chloro­salicylate anion of the title salt, C₅H₆BrN₂⁺·C₇H₄ClO₃⁻, an intra­molecular O—H...O hydrogen bond with an S(6) graph-set motif is formed, so that the anion is essentially planar with a dihedral angle of 1.3 (5)° between the benzene ring and the carboxyl­ate group. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl­ate O atoms via a pair of N—H...O hydrogen bonds, forming an R₂²(8) ring motif. The crystal structure also features N—H...O and weak C—H...O inter­actions, resulting in a layer parallel to the (10-1) plane.

5-Amino-6-methyl­quinolin-1-ium 3-carb­oxy­propano­ate

The asymmetric unit of the title salt, C₁₀H₁₁N₂⁺·C₄H₅O₄⁻, consists of two independent 5-amino-6-methyl­quinolin-1-ium cations and two 3-carb­oxy­propano­ate anions. Both cations are protonated at the pyridine N atoms and are essentially planar, with maximum deviations of 0.026 (3) and 0.016 (2) Å. In the crystal, the cations and anions are linked via N—H...O and O—H...O hydrogen bonds, forming a layer parallel to the ab plane. In the layer, weak C—H...O hydrogen bonds and π–π stacking inter­actions, with centroid-to-centroid distances of 3.7283 (15) and 3.8467 (15) Å, are observed. The crystal structure also features weak C—H...O hydrogen bonds between the layers.

N-But­oxy­carbonyl-5-oxo-L-proline ethyl ester

The mol­ecular structure of the title compound, C₁₂H₁₉NO₅, may be visualized as made up of two nearly perpendicular planes [dihedral angle = 87.39 (12)°] and its crystal structure is a good example of C—H...O inter­actions assuming significance in optimizing supra­molecular aggregation in crystals in a mol­ecule which is severely imbalanced in terms of donors to acceptor atoms. The pyrrolidine ring adopts a (³T₂) twist conformation with puckering parameters Q = 0.2630 (4) Å and φ = 59 (9)°. The crystal structure features R₂⁴(10) and R₃⁴(26) ring motifs formed by four weak C—H...O inter­actions, leading to supra­molecular sheets lying parallel to the bc plane.