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Each mol-ecule of the title compound, C(12)H(18)N(4)O(6), is located on an inversion centre at the mid-point of the central N-N bond. The azo groups C=N of the Schiff base group have an E conformation and the azo groups in the oxime C=N-O groups have a Z conformation. O-H⋯O hydrogen bonds link neighbouring mol-ecules into infinite monolayers perpendicular to the a axis.

The complete mol-ecule of the title compound, C(21)H(26)N(2)O(6), is generated by a crystallographic twofold axis and adopts a trans configuration with respect to the azomethine group. The two benzene rings are almost perpendicular to one another, making a dihedral angle of 89.53 (3)°. In the mol-ecular structure, pairs of intra-molecular O-H⋯N hydrogen bonds generate two six-membered rings. The crystal structure is further stabilized by inter-molecular C-H⋯O hydrogen bonds, which link four adjacent mol-ecules into a network structure.

In the title compound, C(26)H(24)N(4)O(2), the dihedral angles between the central pyrazole ring and the other three benzene rings are 40.02 (3), 77.51 (5) and 55.72 (3)°. A strong intra-molecular N-H⋯O hydrogen bond forms a six-membered ring with an S(6) motif. In the crystal structure, a weak inter-molecular C-H⋯N inter-action with graph-set motif R(2) (2)(8) and C-H⋯O hydrogen bonds link each mol-ecule to three others, forming an infinite two-dimensional supra-molecular structure.

The title compound, [Cu(C(9)H(9)BrNO(2))(2)], is a centrosymmetric mononuclear copper(II) complex. The Cu atom is four-coordinated in a trans-CuN(2)O(2) square-planar geometry by two phenolate O and two oxime N atoms from two symmetry-related N,O-bidentate (E)-4-bromo-2-(ethoxy-imino-meth-yl)phenolate oxime-type ligands. An inter-esting feature of the crystal structure is the centrosymmetric inter-molecular Cu⋯O inter-action [3.382 (1) Å], which establishes an infinite chain structure along the b axis.

In the title compound, C(16)H(16)N(2)O(3)·H(2)O, the benzene rings are nearly coplanar with each other, forming a dihedral angle of 4.46 (3)°. There is a strong intra-molecular O-H⋯N hydrogen bond which results in a six-membered ring. In the crystal, the mol-ecules are connected into a three-dimensional network via O-H⋯O and O-H⋯N inter-molecular hydrogen bonds, forming a centrosymmetric ring along the b axis with graph-set motif R(4) (4)(10). In addition, the short distances between the centroids of six-membered rings [3.555 (1) Å], indicate the existence of π-π stacking inter-actions, which may stabilize the crystal structure.

The title bis-oxime compound, C(19)H(22)N(2)O(2), synthesized by the reaction of 4-methyl-2-hydroxy-benzaldehyde with 1,3-bis-(amino-oxy)propane in ethanol, adopts a V-shaped conformation. The dihedral angle between the rings is 84.59 (3)°. The mol-ecule is disposed about a crystallographic twofold rotation axis, with one C atom lying on the axis. In the crystal, mol-ecules are packed by C-H⋯π(Ph) inter-actions, forming chains.

The complete molecule of title compound, C(17)H(16)N(4)O(6), is generated by a crystallographic twofold axis. Within the mol-ecule, the two benzene units are approximately perpen-dicular, making a dihedral angle of 85.91 (4)°. In the crystal, mol-ecules are linked into a three-dimensional network by C-H⋯O hydrogen bonds and short O⋯O and N⋯O inter-actions, with distances of 2.998 (2) and 2.968 (3) Å, respectively.

In the title complex, [Cu(C(12)H(7)Cl(2)N(2)O)(2)], the Cu(II) center is tetra-coordinated by two phenolic O and two azomethine N atoms from two bidentate 4-chloro-2-[(2-chloro-3-pyrid-yl)imino-meth-yl]phenolate (L) ligands. In the crystal structure, the Cu(II) atom has a distorted square-planar coordination environment. The dihedral angles between the benzene and pyridyl rings are 54.39 (3) and 80.14 (4)°, indicating that the pyridine ring has a considerably weaker steric hindrance. The packing of the mol-ecule is controlled by C-H⋯π(Ph) inter-actions and short O⋯Cl inter-actions [3.196 (4) Å], linking the mol-ecules into a chain-like structure along the c axis.

In the title complex, [Cu(C(12)H(7)BrClN(2)O)(2)], the Cu(II) center is tetra-coordinated by two phenolate O and two azomethine N atoms from two independent bidentate 4-bromo-2-[(2-chloro-3-pyrid-yl)imino-meth-yl]phenolate (L) ligands. In the crystal structure, the Cu(II) atom has a distorted square-planar coordination environment. The inter-planar dihedral angles between the benzene and pyridine rings in the individual ligands are 63.83 (4) and 54.43 (3)°, indicating the pyridine ring to have considerably weaker steric hindrance.

The title complex, [Cu(C(26)H(22)N(2)O(4))], is isostructural with its Ni analogue. All intramolecular distances and angles are very similar for the two structures, whereas the packing of the molecules, including C-H⋯O and C-H⋯π interactions, are slightly different.

The mol-ecule of the title compound, C(31)H(34)N(2)O(4), adopts an L-shaped configuration, in which the naphthalene units are approximately perpendicular, making a dihedral angle of 87.89 (3)°. Intramolecular H-bonds are formed between the OH substituents and the N atoms at each end of the molecule. In the crystal structure, each mol-ecule links six other mol-ecules into an infinite three-dimensional network supra-molecular structure, which is built from one-dimensional zigzag chains via weak C-H⋯π stacking and inter-molecular C-H⋯O hydrogen bonds.