2-Amino-5-methyl-pyridinium 3-hy-droxy-pyridine-2-carboxyl-ate.

In the 3-hy-droxy-picolinate anion of the title salt, C6H9N2 (+)·C6H4NO3 (-), an intra-molecular 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 9.55 (9)° between the pyridine ring and the carboxyl-ate group. In the crystal, the cations and anions are linked via N-H⋯O hydrogen bonds, forming a centrosymmetric 2 + 2 aggregate with R 2 (2)(8) and R 4 (2)(8) ring motifs. The crystal structure also features N-H⋯N and weak C-H⋯π inter-actions.

2-Amino-5-methyl-pyridinium 2-hy-droxy-5-chloro-benzoate.

In the 5-chloro-salicylate anion of the title salt, C6H9N2(+)·C7H4ClO3(-), an intra-molecular O-H⋯O hydrogen bond with an S(6) graph-set motif is observed and the dihedral angle between the benzene ring and the -CO2 group is 1.6 (6)°. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl-ate O atoms via a pair of N-H⋯O hydrogen bonds, forming an R2(2)(8) ring motif. The crystal structure also features N-H⋯O and weak C-H⋯O inter-actions, resulting in a layer parallel to (10-1).

2-Amino-5-methyl-pyridinium 4-chloro-benzoate.

The 4-chloro-benzoate anion of the title salt, C6H9N2(+)·C7H4ClO2(-), is nearly planar with a dihedral angle of 5.14 (16)° between the benzene ring and the carboxyl-ate group. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl-ate O atoms of the anion via a pair of N-H⋯O hydrogen bonds with an R2(2)(8) ring motif. The ion pairs are further connected via N-H⋯O and weak C-H⋯O hydrogen bonds, forming a two-dimensional network parallel to the bc plane. The crystal structure also features a π-π stacking inter-action between the pyridinium and benzene rings with a centroid-centroid distance of 3.7948 (9) Å.

2-Amino-5-methyl-pyridinium 4-methyl-benzoate.

The 4-methyl-benzoate anion of the title salt, C6H9N2(+)·C8H7O2(-), is nearly planar, with a dihedral angle of 6.26 (10)° between the benzene ring and the carboxyl-ate group. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl-ate O atoms of the anion via a pair of N-H⋯O hydrogen bonds with an R2(2)(8) ring motif, forming an approximately planar ion pair with a dihedral angle of 9.63 (4)° between the pyridinium and benzene rings. The ion pairs are further connected via N-H⋯O and weak C-H⋯O hydrogen bonds, forming a two-dimensional network parallel to the bc plane.

(2E)-3-(2-Fluoro-phen-yl)-1-(4-fluoro-phen-yl)prop-2-en-1-one.

In the title compouund, C(15)H(10)F(2)O, the mol-ecule exists in an E conformation with respect to the C=C bond [1.3382 (16) Å]. The dihedral angle between the fluoro-substituted benzene rings is 6.80 (6)° and the whole mol-ecule is roughly planar (r.m.s. deviation for the non-H atoms = 0.069 Å). In the crystal, mol-ecules are linked by C-H⋯F and C-H⋯O inter-actions into sheets lying parallel to the bc plane.

Ethyl 6-(4-meth-oxy-phen-yl)-2-oxo-4-phenyl-cyclo-hex-3-ene-carboxyl-ate.

The asymmetric unit of the title compound, C(22)H(22)O(4), consists of two independent mol-ecules (A and B). The cyclo-hexene rings adopt slightly distorted sofa conformations in both mol-ecules. The dihedral angles between the benzene rings are 74.16 (13) and 71.85 (13)° in mol-ecules A and B, respectively. In the crystal, weak C-H⋯O hydrogen bonds link the mol-ecules into a ribbon-like structure along the b axis. Weak C-H⋯π inter-actions are also observed.

2-Amino-5-methyl-pyridinium trifluoro-acetate.

In the title salt, C6H9N2(+)·C2F3O2(-), the F atoms of the anion are disordered over two sets of sites, with refined occupancies in a ratio of 0.505 (17):0.495 (17). In the crystal, cations and anions are linked via N-H⋯O hydrogen bonds, forming R2(2)(8) ring motifs. The ionic units are linked into a two-dimensional network parallel to (100) by N-H⋯O and weak C-H⋯O hydrogen bonds. The crystal structure is further stabilized by weak C-H⋯F hydrogen bonds, resulting in a three-dimensional network.

Bis(2,6-diamino-4-chloro-pyrimidin-1-ium) fumarate.

In the title salt, 2C4H6ClN4(+)·C4H2O4(2-), the complete fumarate dianion is generated by crystallographic inversion symmetry. The cation is essentially planar, with a maximum deviation of 0.018 (1) Å. In the anion, the carboxyl-ate group is twisted slightly away from the attached plane, the dihedral angle between the carboxyl-ate and (E)-but-2-ene planes being 12.78 (13)°. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl-ate O atoms of the anion via a pair of N-H⋯O hydrogen bonds, forming an R2(2)(8) ring motif. In addition, another type of R2(2)(8) motif is formed by centrosymmetrically related pyrimidinium cations via N-H⋯N hydrogen bonds. These two combined motifs form a heterotetra-mer. The crystal structure is further stabilized by stong N-H⋯O, N-H⋯Cl and weak C-H⋯O hydrogen bonds, resulting a three-dimensional network.

4,6-Dimeth-oxy-2-(methyl-sulfan-yl)pyrimidine-4-hy-droxy-benzoic acid (1/1).

The base mol-ecule of the title co-crystal, C7H10N2O2S·C7H6O3, is essentially planar, with a maximum deviation of 0.0806 (14) Šfor all non-H atoms. The acid mol-ecule is also nearly planar, with a dihedral angle of 8.12 (14)° between the benzene ring and the carb-oxy group. In the crystal, the acid mol-ecules form an inversion dimer through a pair of O-H⋯O hydrogen bonds with an R2(2)(8) ring motif. The pyrimidine mol-ecules are linked on both sides of the dimer into a heterotetra-mer via O-H⋯N and C-H⋯O hydrogen bonds with R2(2)(8) ring motifs. The heterotetra-mers are further linked by weak C-H⋯O hydrogen bonds, forming a tape structure along [1-10].

2-Amino-5-methyl-pyridinium 6-oxo-1,6-dihydro-pyridine-2-carboxyl-ate.

The anion of the title salt, C(6)H(9)N(2) (+)·C(6)H(4)NO(3) (-), undergoes an enol-to-keto tautomerism during the crystallization. In the crystal structure, the cation and anion are held together by a relatively short N-H⋯O hydrogen bond, and the two anions are further connected to each other by a pair of N-H⋯O hydrogen bonds with an R(2) (2)(8) ring motif, thus forming a centrosymmetric 2 + 2 aggregate. The aggregates are further linked through weak N-H⋯O and C-H⋯O hydrogen bonds, resulting a three-dimensional network.

2-Amino-5-methyl-pyridinium 3-chloro-benzoate.

The 3-chloro-benzoate anion of the title salt, C(6)H(9)N(2) (+)·C(7)H(4)ClO(2) (-), is nearly planar with a dihedral angle of 2.44 (13)° between the benzene ring and the carboxyl-ate group. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl-ate O atoms of the anion via a pair of N-H⋯O hydrogen bonds with an R(2) (2)(8) ring motif, forming an approximately planar ion pair with a dihedral angle of 7.92 (5)° between the pyridinium and benzene rings. The ion pairs are further connected via N-H⋯O and C-H⋯O hydrogen bonds, forming a two-dimensional network parallel to the bc plane.

2-Amino-5-methyl-pyridinium 2-amino-benzoate.

In the 2-amino-benzoate anion of the title salt, C(6)H(9)N(2) (+)·C(7)H(6)NO(2) (-), an intra-molecular N-H⋯O hydrogen bond is observed. The dihedral angle between the ring and the CO(2) group is 8.41 (13)°. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl-ate O atoms via a pair of N-H⋯O hydrogen bonds, forming an R(2) (2)(8) ring motif. The ion pairs are further connected via N-H⋯O hydrogen bonds, resulting in a donor-donor-acceptor-acceptor (DDAA) array of quadruple hydrogen bonds. The crystal structure also features a weak N-H⋯O hydrogen bond and a C-H⋯π inter-action, resulting in a three-dimensional network.