2-Amino-3-ammonio­pyridinium dichloride

The asymmetric unit of the title compound, C5H9N3 2+·2Cl−, contains two diprotonated 2,3-diamino­pyridine cations and four chloride anions. In the crystal structure, the anions and cations are connected by inter­molecular N—H⋯Cl and C—H⋯Cl hydrogen bonds, forming a three-dimensional network. The crystal structure is further stabilized by π–π inter­actions between pyridinium rings [centroid–centroid distance = 3.695 (1) Å]

2-Amino-5-methyl­pyridinium nicotinate

In the title compound, C6H9N2 +·C6H4NO2 −, the 2-amino-5-methyl­pyridinium cation is essentially planar, with a maximum deviation of 0.023 (2) Å. In the crystal, the cations and anions are linked via strong N—H⋯O hydrogen bonds, forming a two dimensional network parallel to (100). In addition, π⋯π inter­actions involving the pyridinium and pyridine rings, with centroid–centroid distances of 3.6383 (8) Å, are observed

3,4-Diaminopyridinium 2-carboxy-4,6-dinitrophenolate

In the title salt, C5H8N3 +·C7H3N2O7 −, the pyridine N atom of the 3,4-diamino­pyridine mol­ecule is protonated. The 3,5-dinitro­salicylate anion shows whole-mol­ecule disorder over two orientations with a refined occupancy ratio of 0.875 (4): 0.125 (4). In the crystal, the cations and anions are connected by inter­molecular N—H⋯O and C—H⋯O hydrogen bonds, forming a three-dimensional network

2-Amino-5-chloro­pyridinium (Z)-3-carb­oxy­prop-2-enoate 0.25-hydrate

In the title hydrated salt, C5H6ClN2 +·C4H3O4 −·0.25H2O, the water O atom lies on a twofold axis with 0.25 occupancy. The 2-amino-5-chloro­pyridinium cation is almost planar, with a maximum deviation of 0.015 (3) Å. In the hydrogen malate anion, an intra­molecular O—H⋯O hydrogen bond generates an S(7) ring and results in a folded conformation. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl­ate O atoms of the anion via a pair of N—H⋯O hydrogen bonds, forming an R 2 2(8) ring motif. The ion pairs are further connected via O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, forming layers parallel to the ab plane which stack down the c axis

2-Isopropyl-6-methyl-4-oxo-3,4-dihydro­pyrimidin-1-ium 2-carb­oxy-4,6-dinitro­phenolate monohydrate

In the title mol­ecular salt, C8H13N2O+·C7H3N2O7 −·H2O, the pyrimidinium cation is essentially planar, with a maximum deviation of 0.009 (1) Å. The cation undergoes an enol–keto tautomerism during the crystallization. In the crystal, the ion pairs and water mol­ecules are connected via O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, forming two-dimensional networks parallel to the bc plane. There is an intra­molecular O—H⋯O hydrogen bond in the 3,5-dinitro­salicylate anion, which generates an S(6) ring motif

2-Amino-5-chloro­pyridine–fumaric acid (1/2)

The asymmetric unit of the title compound, C5H5ClN2·0.5C4H4O4, comprises a neutral 2-amino-5-chloro­pyridine mol­ecule and one half of a fumaric acid mol­ecule which lies on an inversion center. The dihedral angle between the pyridine ring and the plane formed by the fumaric acid mol­ecule is 3.22 (8)°. The 2-amino-5-chloro­pyridine mol­ecule is planar, with a maximum deviation of 0.004 (1) Å for the pyridine N atom. In the crystal, the 2-amino-5-chloro­pyridine mol­ecules inter­act with the carboxyl groups of fumaric acid mol­ecules through N—H⋯O and O—H⋯N hydrogen bonds, forming centrosymmetric R 2 2(8) ring motifs and another N—H⋯O hydrogen bond links these motifs into a two-dimensional network parallel to (100)

2-Amino-5-chloro­pyridinium 6-oxo-1,6-dihydro­pyridine-2-carboxyl­ate 0.85-hydrate

In the title salt, C5H6ClN2 +·C6H4NO3 −·0.85H2O, the pyridin­ium ring is planar, with a maximum deviation of 0.010 (2) Å. In the crystal structure, the cations, anions and water mol­ecules are linked via N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds, forming a three-dimensional network

4-Meth­oxy­quinolinium-2-carboxyl­ate dihydrate

The title hydrated quinoline derivative, C11H9NO3·2H2O, crystallizes as a zwitterion in which the quinoline N atom is protonated. The quinoline ring is essentially planar, with a maximum deviation of 0.017 (2) Å. An intra­molecular N—H⋯O hydrogen bond between the protonated N atom and the O atom of the carboxyl­ate group in the zwitterion forms an S(5) ring motif. In the crystal, the zwitterions are connected into inversion dimers via pairs of N—H⋯O and C—H⋯O hydrogen bonds with R 2 2(4) and R 1 2(6) motifs. The water mol­ecules are connected via O—H⋯O hydrogen bonds, forming supra­molecular chains along the c axis. Furthermore, the chains and the dimers are connected via O—H⋯O hydrogen bonds, forming ladder-like supra­molecular ribbons along the c axis

N,N′-Bis(3-chloro-2-fluoro­benzyl­idene)ethane-1,2-diamine

The mol­ecule of the title centrosymmetric Schiff base compound, C16H12Cl2F2N2, adopts an E configuration with respect to the azomethine C=N bond. The imino groups are coplanar with the aromatic rings. Within the mol­ecule, the planar units are parallel, but extend in opposite directions from the dimethyl­ene bridge. An inter­esting feature of the crystal structure is the short inter­molecular Cl⋯F [3.1747 (5) Å] inter­actions, which are shorter than the sum of the van der Waals radii of these atoms. These inter­actions link neighbouring mol­ecules along the b axis. The crystal structure is further stabilized by π–π inter­actions, with a centroid–centroid distance of 3.5244 (4) Å

(E)-1,2-Bis(4-fluoro­phen­yl)ethane-1,2-dione

The title compound, C14H8F2O2, is a substituted benzil with an s-trans conformation of the dicarbonyl unit. This conformation is also shown by the O—C—C—O torsion angle of −110.65 (12)°. An unusual feature of the structure is the length, 1.536 (2) Å, of the central C—C bond connecting the carbonyl units, which is significantly longer than a normal Csp 2—Csp 2 single bond. This is probably the result of decreasing the unfavourable vicinal dipole–dipole inter­actions by increasing the distance between the two electronegative O atoms [O⋯O = 3.1867 (12) Å] and allowing orbital overlap of the dione with the π system of the benzene rings. The dihedral angle between the aromatic rings is 64.74 (5)°. In the crystal structure, neighbouring mol­ecules are linked together by weak inter­molecular C—H⋯O (× 2) hydrogen bonds. In addition, the crystal structure is further stabilized by inter­molecular π–π inter­actions with centroid–centroid distances in the range 3.6416 (6)–3.7150 (7) Å