Crystal structures of 2-amino-pyridine citric acid salts: C5 H7 N2 + ·c6 H7 O7 - And 3C5 H7 N2 + ·c6 H5 O7 3-
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2-Amino-pyridine and citric acid mixed in 1:1 and 3:1 ratios in ethanol yielded crystals of two 2-amino-pyridinium citrate salts, viz. C5 H7 N2 +·C6 H7 O7 - (I) (systematic name: 2-amino-pyridin-1-ium 3-carb-oxy-2-carb-oxy-methyl-2-hy-droxy-propano-ate), and 3C5 H7 N2 +·C6 H5 O7 3- (II) [systematic name: tris-(2-amino-pyridin-1-ium)2-hy-droxy-propane-1,2,3-tri-carboxyl-ate]. The supra-molecular 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 carb-oxy-lic group of citric acid, while in II all three carb-oxy-lic groups of the acid are deprotonated and the charges are compensated for by three 2-amino-pyridinium cations. In both structures, a complex supra-molecular three-dimensional architecture is formed. In I, the supra-molecular 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 inter-actions. The mol-ecular conformation of the citrate ion (CA 3-) in II is stabilized by an intra-molecular 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-amino-pyridinium-carboxyl-ate heterosynthon exhibited in many 2-amino-pyridinium carboxyl-ates 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-amino-pyridinium-carboxyl-ate 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. © 2018 Prakash et al.

Acta Crystallographica Section E: Crystallographic Communications
International Union of Crystallography
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