Single crystals of the title compound, C(10)H(11)NO(4), an inter-mediate in the industrial synthesis of yellow azo pigments, were obtained from the industrial production. The mol-ecules crystallize as centrosymmetic dimers connected by two symmetry-related N-H⋯O=C hydrogen bonds. Each mol-ecule also contains an intra-molecular N-H⋯O=C hydrogen bond. The dimers form stacks along the a-axis direc...

Theere are two independent mol-ecules in the asymmetric unit of the title compound, C(14)H(11)FN(2)O(2), each with a trans configuration with respect to the azo double bond. The dihedral angle between the aromatic rings is 17.21 (2)° in one mol-ecule and 19.06 (2)° in the other. Each of the independent mol-ecules has an intra-molecular O-H⋯O hydrogen bond. In the crystal, mol-ecules are stacked...

The title compound, C(15)H(14)N(2)O(2), an azo dye, displays a trans configuration with respect to the N=N bridge. The dihedral angle between the aromatic rings is 0.18 (14)°. There is a strong intra-molecular O-H⋯O hydrogen bond. Geometrical parameters, determined using X-ray diffraction techniques, are compared with those calculated by density functional theory (DFT), using hybrid exchange-co...

The title compound, C(13)H(14)N(4), adopts a trans configuration about the azo bond. There is a dihedral angle of 12.18 (7)° between the pyridine and benzene rings and the mean plane of the dimethyl-amino substituent is twisted by 6.1 (2)° relative to the benzene ring. In the crystal, weak inter-molecular C-H⋯N hydrogen bonds result in a zigzag arrangement along [010].

In the title compound, C(27)H(17)N(3)O(4), the azo group displays a trans conformation and the dihedral angles between the central benzene ring and the pendant anthracene and nitro-benzene rings are 82.94 (7) and 7.30 (9)°, respectively. In the crystal structure, weak C-H⋯O hydrogen bonds, likely associated with a dipole moment present on the mol-ecule, help to consolidate the packing.

In the title compound, C(24)H(28)N(4)O(2) (2+)·2Br(-)·2H(2)O, the diimid-azo-lium cation is located on an inversion center. The imidazole and the benzene rings make a dihedral angle of 68.08 (04)°. In the crystal, O-H⋯Br, C-H⋯O and C-H⋯Br hydrogen bonds link the diimidazolium cations, the bromide anions and the water mol-ecules into a two-dimensional network.

In the title compound, [Cu(C21H19N6O2)Cl], the Cu(II) atom is in a slightly distorted square-planar coordination involving two O atoms from the pyrazolone rings [Cu-O = 2.088 (10) and 1.975 (10) Å], an N atom of the azo group [Cu-N = 2.048 (13) Å] and a chloride anion [Cu-Cl = 2.183 (5) Å]. The organic anions act as tridentate chelating ligands. The mol-ecules stack in columns along the c axis.

The structure of the title compound, C(15)H(14)N(2)O(2), an azo dye, displays a trans configuration with respect to the N=N bridge. The dihedral angle between the aromatic rings is 5.06 (8)°. The mol-ecular conformation is stabilized by a strong intra-molecular O-H⋯O hydrogen bond. In the crystal, inter-molecular C-H⋯O hydrogen bonds occur.

The title compound, C(16)H(10)N(2)O(8)·2C(3)H(7)NO, was synthesized by the reductive condensation reaction of 5-nitro-isophthalic acid in the presence of NaOH. The tetra-acid mol-ecule, which has a crystallographically imposed centre of symmetry, adopts an E configuration with respect to the azo group. In the crystal packing, mol-ecules are linked through inter-molecular O-H⋯O and C-H⋯O hydroge...

In the crystal structure of the title compound, C(16)H(10)N(2)O(8)·2H(2)O, the organic mol-ecule is located on a centre of symmetry. The two benzene rings are parallel, but not coplanar, as indicated by N=N-C-C torsion angles involving the azo group of 12.1 (5) and -168.2 (3)°. The organic mol-ecule and the water mol-ecule are linked by O-H⋯O hydrogen bonds, forming a three-dimensional network.