Crystal structures of 2-amino­pyridine citric acid salts: C(5)H(7)N(2) (+)·C(6)H(7)O(7) (−) and 3C(5)H(7)N(2) (+)·C(6)H(5)O(7) (3−)

2-Amino­pyridine and citric acid mixed in 1:1 and 3:1 ratios in ethanol yielded crystals of two 2-amino­pyridinium citrate salts, viz. C(5)H(7)N(2) (+)·C(6)H(7)O(7) (−) (I) (systematic name: 2-amino­pyridin-1-ium 3-carb­oxy-2-carb­oxy­methyl-2-hy­droxy­propano­ate), and 3C(5)H(7)N(2) (+)·C(6)H(5)O(7) (3−) (II) [systematic name: tris­(2-amino­pyridin-1-ium) 2-hy­droxy­propane-1,2,3-tri­carboxyl­ate]. The supra­molecular synthons present are analysed and their effect upon the crystal packing is presented in the context of crystal engineering. Salt I is formed by the protonation of the pyridine N atom and deprotonation of the central carb­oxy­lic group of citric acid, while in II all three carb­oxy­lic groups of the acid are deprotonated and the charges are compensated for by three 2-amino­pyridinium cations. In both structures, a complex supra­molecular three-dimensional architecture is formed. In I, the supra­molecular aggregation results from N(amino)—H⋯O(acid), O(acid)⋯H—O(acid), O(alcohol)—H⋯O(acid), N(amino)—H⋯O(alcohol), N(py)—H⋯O(alcohol) and C(ar)—H⋯O(acid) inter­actions. The mol­ecular conformation of the citrate ion (CA(3−)) in II is stabilized by an intra­molecular O(alcohol)—H⋯O(acid) hydrogen bond that encloses an S(6) ring motif. The complex three-dimensional structure of II features N(amino)—H⋯O(acid), N(py)—H⋯O(acid) and several C(ar)—H⋯O(acid) hydrogen bonds. In the crystal of I, the common charge-assisted 2-amino­pyridinium–carboxyl­ate heterosynthon exhibited in many 2-amino­pyridinium carboxyl­ates is not observed, instead chains of N—H⋯O hydrogen bonds and hetero O—H⋯O dimers are formed. In the crystal of II, the 2-amino­pyridinium–carboxyl­ate heterosynthon is sustained, while hetero O—H⋯O dimers are not observed. The crystal structures of both salts display a variety of hydrogen bonds as almost all of the hydrogen-bond donors and acceptors present are involved in hydrogen bonding.