Crystal structure, characterization and Hirshfeld analysis of bis{(E)-1-[(2,4,6-tribromophenyl)diazenyl]naphthalen-2-olato}copper(II) dimethyl sulfoxide monosolvate

In the title CuII complex, a newly synthesized dye, 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-olate ligands.

In the title compound, [Cu(C 16 H 8 Br 3 N 2 O) 2 ]ÁC 2 H 6 OS, the Cu II atom is tetracoordinated in a square-planar coordination, being surrounded by two N atoms and two O atoms from two N,O-bidentate (E)-1- [(2,4,6-tribromophenyl)diazenyl]naphthalen-2-olate ligands. The two N atoms and two O atoms around the metal center are trans to each other, with an O-Cu-O bond angle of 177.90 (16) and a N-Cu-N bond angle of 177.8 (2) . The average distances between the Cu II atom and the coordinated O and N atoms are 1.892 (4) and 1.976 (4) Å , respectively. In the crystal, complexes are linked by C-HÁ Á ÁO hydrogen bonds and byinteractions involving adjacent naphthalene ring systems [centroid-centroid distance = 3.679 (4) Å ]. The disordered DMSO molecules interact weakly with the complex molecules, being positioned in the voids left by the packing arrangement of the square-planar complexes. The DMSO solvent molecule is disordered over two positions with occupancies of 0.70 and 0.30.

Chemical context
Azo dyes are an important class of organic compounds that are attractive to researchers because of their various applications (Zollinger, 1961;Nishihara, 2004;Sahoo et al., 2015). They constitute the largest group of azo compounds and are the most widely used colorants in the industry. Applications of azo dyes include their use as coloring agents because of their affinity for wool and silk (Patel et al., 2011), in photoelectronics (Sekar, 1999), optical storage technology (Wang et al., 2000), biological reactions (Wę glarz-Tomczak et al., 2012), printing systems (Abe et al., 1999;Dharmalingam et al., 2011), in analytical areas (Abdalla et al., 2013;Amin et al., 2003) and in the food industry (Almeida et al., 2010). Azo derivatives and their metal complexes are important homologue pigments for synthetic leather and vinyl polymers. Furthermore, azo compounds are known to be involved in a number of biological reactions, such as inhibition of DNA, RNA, and protein synthesis, nitrogen fixation and carcinogenesis (Badea et al., 2004). In addition, high-density optical data storage has ISSN 2056-9890 been the subject of extensive research over the past decade. In general, cyanine dyes, phthalocyanine dyes, and metal-azo dyes are used in the recording layer of DVD-R (digital versatile disc-recordable) discs. It was reported that the new technology, which employs 405 nm blue-violet diode lasers, will require a new optical-recording medium matching the 405 nm wavelength laser (Steed et al., 2007). In comparison with the dyes themselves, metal-azo dyes are light-stable, allow an easier control of the wavelength by selection of the appropriate substituent groups, and have good thermal stability (Geng et al., 2004;Bin et al., 2003;Fu-Xin et al., 2003;Hamada et al., 1997;Suzuki et al., 1999;Nejati et al., 2009;Li et al., 2010). Being interested in the synthesis and preparation of metal complexes bearing such ligands, we have synthesized and structurally characterized Cu II complexes with N,Obidentate phenylazo-naphtholate ligands (Chetioui et al., 2015a,b). In our previous work, we were interested by the colour-generation mechanism of azo pigments, usually characterized by the chromophore of the azo group (-N N-) (Bougueria et al., 2013a(Bougueria et al., ,b,c, 2014Chetioui et al., 2013a,b). Herein, we report the synthesis and crystal structure of a Cu II complex incorporating the ligand (E)-1-[(2,4,6-tribromophenyl)diazenyl]naphthalen-2-ol, for which the structure is known (Chetioui et al., 2013a).

Structural commentary
The structure of the title compound is shown in Fig. 1. The asymmetric unit consists of a Cu II complex molecule and a DMSO solvent molecule. In the complex, the Cu II atom is coordinated by two oxygen and two nitrogen atoms trans to each other. The Cu1-N2 and Cu1-N4 bond lengths [1.976 (4) and 1.971 (5) Å , respectively] are almost identical. The N-Cu-N bond angle is 177.8 (2) . The two Cu-O distances are 1.882 (4) and 1.892 (4) Å . All bond lengths are similar to those observed in similar crystal structures (Chetioui et al., 2015a,b). The N-Cu-O bond angles range from 88.75 (18) to 93.06 (17) and the O-Cu-O angle is 177.90 (16) . Therefore, the copper atom can be considered to be in a slightly distorted square-planar geometry. The dihedral angle formed between the plane of the C1-C10 naphthalene ring system and the tribromobenzene ring is 51.4 (2) .

Figure 1
The molecular structure of the title compound with atom labelling and displacement ellipsoids drawn at the 50% probability level.

Synthesis and crystallization
The complex, bis-1-(2,4,6-tribromophenylazo)-2-naphtholatecopper(II), was obtained by mixing 1 mmol of 1-(2,4,6tribromophenylazo)-2-naphthol dissolved in 20 ml of THF with 0.5 mmol of Cu(OAc) 2 ÁH 2 O dissolved in 20 ml of MeOH. The mixture was refluxed at 333 K for 8 h. Upon cooling, a dark-orange solid was observed, which was filtered off and washed with water, and then dried under vacuum. Crystallization in DMSO yielded 83% of a crystalline material. To confirm the formula of the solvate complex, an elementary analysis was carried out: calculated for C 32 H 16 Br 6 CuN 4 O 2 Á-C 2 H 6 OS, C 36.80%, N 5.05%, H 2.00%, found C 36,27%, N 4,81%, H 1,92%. The 1 H NMR spectrum (paramagnetic complex) shows a multiplet around 7 and 8 ppm attributed to the aromatic protons. The IR spectrum of the complex shows the vibration bands:  A view along the a axis of the crystal packing of the title compound.

Figure 3
View of the Hirshfeld surface mapped over d norm .

Figure 4
Two-dimensional fingerprint plots of the compound showing (a) all interactions and those delineated into

Refinement
Crystal data, data collection and structure refinement details are summarized in   program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.68 e Å −3 Δρ min = −0.50 e Å −3 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 Occ. (