Bis{μ-2,2′-[(3,4-dithiahexane-1,6-diyl)bis(nitrilomethanylylidene)]bis(4-bromophenolato)-κ4 O,N,N′,O′}dicopper(II)

The crystal structure of a novel binuclear copper(II) complex with a dianionic Schiff base derived from 5-bromosalicylic aldehyde and cysteamine prepared by direct synthesis is reported.


Chemical context
Schiff bases and their metal complexes represent one of the most widely used classes of compound because of their synthetic flexibility and wide range of applications (Mitra et al., 1997;Bera et al., 1998;Prabhakaran et al., 2004). Such complexes having sulfur-containing ligands are of considerable interest because of their diverse coordination modes and bridging ability. The formation and cleavage of disulfide bonds are known to be important for the biological activity of several sulfur-containing peptides and proteins (Gilbert et al., 1999;Jacob et al., 2003).
In this study we have continued our investigations in the field of direct synthesis, which is an efficient method to obtain novel polynuclear complexes (Babich & Kokozay, 1997;Vinogradova et al., 2001;Nesterova et al., 2008). The title compound was prepared by direct synthesis starting from zero-valent Cu with a Schiff-base ligand, the product of condensation between 5-bromsalicylaldehyde and cysteamine, formed in situ in a methanol/dimethylformamide (DMF) mixture. ISSN 2056-9890
The chelating fragments coordinated to the Cu II ions are twisted relative to each other, as defined by the dihedral angle of 28.9 (2) formed between the mean planes of atoms O1/N1/ C1/C6/C7 and O2/N2/C8/C13/C14. The thiosulfonate moiety is not involved in any metal-ligand interactions.
The separation between the two symmetry-related Cu II ions within the binuclear fragment is 5.2161 (11) Å and between neighboring fragments is 3.4458 (11) Å . In general, all bonding parameters and the dimensions of the angles in the title complex are in good agreement with those encountered in related complexes (Dhar et al., 2005;Zhang et al., 2010).
In contrast to the previously reported complex (Rusanova & Bederak, 2017), there are no hydrogen-bond orstacking interactions in the title complex. In terms of C-HÁ Á ÁBr interactions, the intermolecular C16-H16BÁ Á ÁBr2(x + 1, y, z) distance of 3.03 Å and C17-H17BÁ Á ÁS1(À 1 2 + x, 1 2 À y, À 1 2 + z) distance of 2.95 Å are almost equal to the sum of the van der Waals radii for the atoms involved and may be worthy of note. The crystal packing of the title compound viewed along the a axis. Short SÁ Á ÁBr contacts are shown as dashed lines. H atoms are not shown.

Figure 3
The crystal packing of the title compound viewed along the b axis. Short SÁ Á ÁBr contacts are shown as dashed lines. H atoms are not shown.

Figure 1
The molecular structure of the binuclear complex unit of the title compound, showing 50% probability displacement ellipsoids. Unlabelled atoms are related to labelled ones by the symmetry operation (2 À x, Ày, (Dhar et al., 2004(Dhar et al., , 2005. The length of the SÁ Á ÁBr contact in the title compound is in good agreement with those in related complexes (CSD refcodes WEMCAT and QELVIN; Salivon et al., 2006Salivon et al., , 2007CSD refcode PODDAO;Xia et al., 2008)

Synthesis and crystallization
A solution of KOH (0.12 g, 2 mmol) in a minimum amount of methanol was added to a solution of aminoethanethiol hydrochloride (0.23g, 2 mmol) in methanol (5 ml) and stirred on an ice bath for 10 min. The white precipitate of solid KCl was removed by filtration and 5-bromsalicylaldehyde (0.402 g, 2 mmol) in dimethylformamide (10 ml) were added to the filtrate and stirred magnetically for 50 min. Copper powder (0.064 g, 1 mmol) were added to the yellow solution of the Schiff base formed in situ, and the resulting deep green-brown solution was stirred magnetically and heated in air at 323-333 K for 2 h, resulting in a dark-green precipitate. Crystals suitable for crystallographic study were grown from a saturated solution in DMF after successive addition of CH 2 Cl 2 . The crystals were filtered off, washed with dry i-PrOH and finally dried at room temperature (yield: 20%).
The IR spectrum of the title compound (as KBr pellets) is consistent with the above structural data. In the range 4000-400 cm À1 it shows all characteristic functional groups peaks: (CH) due to aromatic C-H stretching at 3000-3100cm À1 , the aromatic ring vibrations in the 1600-1400 cm À1 region, weak S-S absorptions at 500-540 cm À1 as well absorbance at 1630 cm À1 assigned to the azomethine (C N) group. Analysis calculated for C 36 H 32 Br 4 Cu 2 N 4 O 4 S 4 : C37.28, H 2.78, N 4.83, S 11.06%; found: C 37.32, H 3.01, N 4.70, S 11.10%.

Bis{µ-2,2′-[(3,4-dithiahexane-1,6-diyl)bis(nitrilomethanylylidene)]bis(4-bromophenolato)κ 4 O,N,N′,O′}dicopper(II)
Crystal data 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.