Crystal structures of a copper(II) and the isotypic nickel(II) and palladium(II) complexes of the ligand (E)-1-[(2,4,6-tribromophenyl)diazenyl]naphthalen-2-ol

In the title copper(II) complex, the metal atom is coordinated by two N atoms and two O atoms from two bidentate (E)-1-[(2,4,6-tribromophenyl)diazenyl]naphthalen-2-ol ligands, forming a slightly distorted square-planar environment. In the isotypic nickel(II) and palladium(II) complexes, the metal atoms are located on centres of inversion, hence the metal coordination spheres have perfect square-planar geometries.


Chemical context
Recently, 1-phenylazo-2-naphthol derivatives have attracted attention because the phenylazo-naphtholate group can provide N,O-bidentate chelation to stabilize transition or main group metal complexes. Azo-metal chelates have also attracted increasing attention due to their interesting electronic and geometrical features in connection with their applications in molecular memory storage, non-linear optical elements and printing systems. Another advantage of ISSN 2056-9890 complexes involving azo DNO's (dyes and pigments) and transition metal ions is the possibility to obtain new compounds with biological activity (Thomas et al., 2004;Reed et al., 2006). Transition metals have also been used in the treatment of several diseases, as metal complexes which are capable of cleaving DNA under physiological conditions are of interest in the development of metal-based anticancer agents. This is an impetus for chemists to develop innovative strategies for the preparation of more effective, target-specific and preferably non-covalently bound anticancer drugs (Chen et al., 2010;Cvek et al., 2008).
Being interested in the synthesis and preparation of metal complexes bearing such ligands, we have successfully synthesized and structurally characterized Cu II complexes with N,Obidentate phenylazo-naphtholate ligands (Chetioui et al., 2015a,b). In this work we are involved in the colour-generation mechanism of azo pigments typically characterized by the chromophore of the azo group (-N N-) (Chetioui et al., 2013c,d) in order to synthesize new complexes with Cu(OAc) 2 ÁH 2 O, Ni(OAc) 2 ÁH 2 O, and Pd(OAc) 2 ÁH 2 O. We report herein on the synthesis and crystal structures of the title complexes, (I)-(III), of the ligand (E)-1-[(2,4,6-tribromophenyl)diazenyl]naphthalen-2-ol, whose crystal structure has been described previously (Chetioui et al., 2013c).

Figure 1
The molecular structure of compound (I), with atom labelling and 50% probability displacement ellipsoids. The intramolecular CuÁ Á ÁBr contact is shown as a dashed line (details are given in Table 1).
Compounds (II) and (III), the nickel(II) (Fig. 2, Table 2) and palladium(II) (Fig. 3, Table 3) complexes, respectively, are isotypic. The metal atoms are each located on inversion centres, coordinating in a bidentate fashion to the N and O atoms of the ligand, hence the metal coordination spheres have perfect square-planar geometry. The tribromobenzene rings (C1-C6) are almost normal to the naphthalene ring systems (C7-C16) with a dihedral angle of 80.79 (18)  The molecular structure of compound (II), with atom labelling and 50% probability displacement ellipsoids. The unlabelled atoms are related to the labelled atoms by the symmetry operation (Àx + 1, Ày + 1, Àz + 1).

Figure 4
The crystal packing of compound (I), viewed along the a axis. The intermolecular interactions are shown as dashed lines (see Table 4 for details), and for clarity only the H atoms involved in these interactions have been included.

Supramolecular features
As shown in Fig. 4, in the crystal of compound (I), molecules are linked by C-HÁ Á ÁBr hydrogen bonds, forming chains along [001]. The chains are linked by C-HÁ Á Á interactions, forming sheets lying parallel to (011). Details of these interactions are given in Table 4. The crystal packing in compound (II) [and isotypic compound (III)] is illustrated in Fig. 5. Molecules are linked by C-HÁ Á Á interactions, forming slabs lying parallel to (101). Details of the intermolecular interactions are given in Table 5 for (II) and Table 6 for (III).

Database survey
In the title ligand (E)-1- [(2,4,6-tribromophenyl)  The crystal packing of compound (II), viewed along the normal to (101). The intermolecular interactions are shown as dashed lines (see Table 5 for details), and for clarity only the H atoms involved in these interactions have been included. Table 4 Hydrogen-bond geometry (Å , ) for (I).

Synthesis and crystallization
The title compounds were synthesized by the following procedure: (E)-1-[(2,4,6-tribromophenyl)diazenyl]-naphthalen-2-ol (2.0 mmol) and M(OAc) 2 ÁH 2 O (1.0 mmol; where M = Cu, Ni, Pd) was stirred at 298 K in a mixture of THF/MeOH (10/10 ml) for 24 h. The solvents were removed under vacuum and the residue was washed twice with hexane to give dark solids. The resulting solids were crystallized from CH 2 Cl 2 to yield red block-like crystals for (I), black prismatic crystals for (II) and dark-red plate-like crystals for (III).

(I) Bis{(E)-1-[(2,4,6-tribromophenyl)diazenyl]naphthalen-2-olato}copper(II)
Crystal data  (14) Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq