Bis{μ-2,2'-[(3,4-di-thia-hexane-1,6-di-yl)bis-(nitrilo-methanylyl-idene)]bis-(4-bromo-phenolato)-κ4O,N,N',O'}dicopper(II).

The crystal structure of the title compound, [Cu2(C18H12Br2N4O2S2)2], consists of binuclear complex units which lie across inversion centres and are connected by weak Cu-O coordination bonds forming chains along the b axis. The CuII ion is five-coordinated by two N atoms and two O atoms of the chelating ligand and one symmetry-related O atom forming a square-pyramidal coordination geometry. In the crystal, short S⋯Br contacts connect neighbouring chains into a two-dimensional network parallel to (101).

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.

Structural commentary

In the title compound, binuclear complex units lie across an inversion centre (Fig. 1 ▸). The coordination geometry around the CuII ion is comparable to that found in copper complexes reported earlier (CSD refcode FEDCIB; Dhar et al., 2005 ▸; Rusanova & Bederak, 2017 ▸). Despite the close structural similarity, neighboring centrosymmetric binuclear fragments are connected by additional weak Cu⋯O (2 − x, 1 − y, 2 − z) coordination bonds with the oxygen atoms of the ligand [2.520 (3) Å] and organized in chains along the b-axis direction (Fig. 2 ▸). Thus, each CuII ion is five-coordinated by two nitro­gen atoms (N1, N2), two oxygen atoms (O1, O2) and one symmetry-related O atom [O1 (2 − x, 1 − y, 2 − z)], forming a distorted square-pyramidal geometry.

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 − x, −y, 2 − z).

Figure 2

The crystal packing of the title compound viewed along the a axis. Short S⋯Br contacts are shown as dashed lines. H atoms are not shown.

The chelating fragments coordinated to the CuII 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 CuII 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 ▸).

Supra­molecular features

In the crystal, short S⋯Br(− + x,  − y,  + z) contacts with a distance of 3.5108 (13) Å connect neighboring chains, forming a two-dimensional network parallel to (101) (Fig. 3 ▸).

Figure 3

The crystal packing of the title compound viewed along the b axis. Short S⋯Br contacts are shown as dashed lines. H atoms are not shown.

In contrast to the previously reported complex (Rusanova & Bederak, 2017 ▸), there are no hydrogen-bond or π-π stacking inter­actions in the title complex. In terms of C—H⋯Br inter­actions, the inter­molecular C16—H16B⋯Br2(x + 1, y, z) distance of 3.03 Å and C17—H17B⋯S1(− + x,  − y, − + 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.

Database survey

A search of the Cambridge Structural Database (Version 5.38; last update November 2016; Groom et al., 2016 ▸) for related complexes with an amino­ethane­thiol group gave 165 hits, including two closely related structures with a di­sulfide moiety, viz. bis­[(μ2-sulfato)(6-salicyl­idene­amino-3,4-di­thia­hexyl­ammonium]­copper(II) and bis­(μ2-N,N′-(3,4-di­thia­hexane-1,6-di­yl)bis­(salicylideneiminato)-N,N′,O,O′)dicopper(II) (Dhar et al., 2004 ▸, 2005 ▸). The length of the S⋯Br contact in the title compound is in good agreement with those in related complexes (CSD refcodes WEMCAT and QELVIN; Salivon et al., 2006 ▸, 2007 ▸; CSD 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 CH2Cl2. 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−1 it shows all characteristic functional groups peaks: ν(CH) due to aromatic =C—H stretching at 3000–3100cm−1, the aromatic ring vibrations in the 1600–1400 cm−1 region, weak S–S absorptions at 500–540 cm−1 as well absorbance at 1630 cm−1 assigned to the azomethine ν(C=N) group. Analysis calculated for C36H32Br4Cu2N4O4S4: C37.28, H 2.78, N 4.83, S 11.06%; found: C 37.32, H 3.01, N 4.70, S 11.10%.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1 ▸. All hydrogen atoms were placed at calculated positions (C–H = 0.93–0.97 Å) and refined as riding with U iso(H) = 1.2U eq(C).

Table 1

Experimental details

Crystal data
Chemical formula	[Cu2(C18H16Br2N2O2S2)2]
M r	1159.61
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	296
a, b, c (Å)	12.3596 (5), 8.3442 (3), 19.5002 (7)
β (°)	95.156 (2)
V (Å3)	2002.94 (13)
Z	2
Radiation type	Mo Kα
μ (mm−1)	5.31
Crystal size (mm)	0.45 × 0.10 × 0.06
Data collection
Diffractometer	Bruker SMART APEXII
Absorption correction	Multi-scan SADABS
T min, T max	0.36, 0.74
No. of measured, independent and observed [I > 2σ(I)] reflections	18553, 3939, 2644
R int	0.075
(sin θ/λ)max (Å−1)	0.617
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.046, 0.098, 1.05
No. of reflections	3939
No. of parameters	244
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.82, −0.66

Computer programs: SMART and SAINT (Bruker, 2008 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL2016 (Sheldrick, 2015b ▸), SHELXTL (Sheldrick, 2008 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989017017790/lh5862sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989017017790/lh5862Isup2.hkl

CCDC reference: 1810837

Additional supporting information: crystallographic information; 3D view; checkCIF report

[Cu2(C18H16Br2N2O2S2)2]	F(000) = 1140
Mr = 1159.61	Dx = 1.923 Mg m−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 12.3596 (5) Å	Cell parameters from 2534 reflections
b = 8.3442 (3) Å	θ = 2.7–23.6°
c = 19.5002 (7) Å	µ = 5.31 mm−1
β = 95.156 (2)°	T = 296 K
V = 2002.94 (13) Å3	Needle, green
Z = 2	0.45 × 0.10 × 0.06 mm

Bruker SMART APEXII diffractometer	3939 independent reflections
Radiation source: sealed tube	2644 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.075
phi and ω scans	θmax = 26.0°, θmin = 1.9°
Absorption correction: multi-scan sadabs	h = −15→8
Tmin = 0.36, Tmax = 0.74	k = −10→10
18553 measured reflections	l = −23→24

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.046	H-atom parameters constrained
wR(F2) = 0.098	w = 1/[σ2(Fo2) + (0.0426P)2] where P = (Fo2 + 2Fc2)/3
S = 1.05	(Δ/σ)max = 0.004
3939 reflections	Δρmax = 0.82 e Å−3
244 parameters	Δρmin = −0.66 e Å−3

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.

	x	y	z	Uiso*/Ueq
BR1	1.46222 (5)	0.24549 (7)	0.82836 (3)	0.04443 (19)
BR2	0.40450 (5)	0.21977 (8)	1.11957 (3)	0.0456 (2)
CU1	0.95419 (5)	0.30506 (7)	1.00084 (3)	0.01799 (16)
N1	1.0809 (3)	0.1638 (4)	1.03365 (18)	0.0184 (9)
N2	0.8169 (3)	0.3643 (4)	0.94366 (18)	0.0174 (9)
O1	1.0408 (2)	0.4239 (3)	0.94197 (15)	0.0184 (7)
O2	0.8768 (3)	0.2123 (4)	1.07014 (16)	0.0239 (8)
S1	1.10722 (11)	−0.01078 (14)	1.23102 (6)	0.0231 (3)
S2	1.21861 (10)	−0.17845 (15)	1.20755 (6)	0.0229 (3)
C1	1.1308 (4)	0.3764 (5)	0.9170 (2)	0.0187 (11)
C2	1.1648 (4)	0.4542 (5)	0.8585 (2)	0.0241 (12)
H2	1.120805	0.533137	0.836940	0.029*
C3	1.2610 (4)	0.4166 (6)	0.8324 (2)	0.0279 (13)
H3	1.282029	0.470919	0.794135	0.033*
C4	1.3278 (4)	0.2961 (6)	0.8634 (3)	0.0265 (12)
C5	1.2960 (4)	0.2146 (6)	0.9191 (3)	0.0261 (12)
H5	1.340017	0.133916	0.939219	0.031*
C6	1.1973 (4)	0.2517 (5)	0.9464 (2)	0.0205 (11)
C7	1.1680 (4)	0.1571 (5)	1.0031 (2)	0.0184 (11)
H7	1.218760	0.081147	1.019849	0.022*
C8	0.7732 (4)	0.2183 (5)	1.0778 (2)	0.0193 (11)
C9	0.7380 (4)	0.1630 (6)	1.1407 (2)	0.0260 (12)
H9	0.788849	0.123649	1.174609	0.031*
C10	0.6303 (4)	0.1663 (6)	1.1528 (3)	0.0247 (12)
H10	0.608900	0.131899	1.194901	0.030*
C11	0.5537 (4)	0.2208 (6)	1.1021 (3)	0.0282 (12)
C12	0.5833 (4)	0.2746 (6)	1.0406 (3)	0.0287 (13)
H12	0.530635	0.311494	1.007245	0.034*
C13	0.6938 (4)	0.2746 (5)	1.0273 (2)	0.0214 (11)
C14	0.7216 (4)	0.3439 (5)	0.9635 (2)	0.0206 (11)
H14	0.663784	0.377719	0.933102	0.025*
C15	1.0733 (4)	0.0487 (5)	1.0908 (2)	0.0191 (11)
H15A	1.121681	−0.040961	1.085098	0.023*
H15B	0.999770	0.007538	1.089495	0.023*
C16	1.1034 (4)	0.1278 (6)	1.1595 (2)	0.0222 (12)
H16A	1.051164	0.211612	1.166482	0.027*
H16B	1.174199	0.177672	1.158804	0.027*
C17	0.8220 (4)	0.4465 (5)	0.8773 (2)	0.0219 (11)
H17A	0.865362	0.542817	0.884674	0.026*
H17B	0.749153	0.478879	0.860140	0.026*
C18	0.8697 (4)	0.3449 (5)	0.8229 (2)	0.0212 (11)
H18A	0.939036	0.302111	0.841906	0.025*
H18B	0.883066	0.412405	0.784101	0.025*

	U11	U22	U33	U12	U13	U23
BR1	0.0376 (4)	0.0474 (4)	0.0522 (4)	−0.0041 (3)	0.0256 (3)	−0.0010 (3)
BR2	0.0234 (3)	0.0744 (5)	0.0400 (4)	−0.0008 (3)	0.0092 (3)	−0.0080 (3)
CU1	0.0192 (3)	0.0175 (3)	0.0170 (3)	0.0009 (3)	0.0002 (2)	0.0026 (3)
N1	0.028 (2)	0.017 (2)	0.010 (2)	−0.0013 (18)	−0.0003 (18)	−0.0023 (16)
N2	0.024 (2)	0.015 (2)	0.013 (2)	0.0012 (17)	−0.0001 (18)	−0.0034 (16)
O1	0.0209 (19)	0.0170 (18)	0.0174 (17)	0.0007 (14)	0.0019 (15)	0.0013 (14)
O2	0.0197 (19)	0.029 (2)	0.0229 (18)	0.0018 (15)	0.0025 (15)	0.0086 (15)
S1	0.0316 (7)	0.0187 (7)	0.0190 (7)	0.0033 (6)	0.0029 (6)	0.0010 (5)
S2	0.0253 (7)	0.0192 (7)	0.0229 (7)	0.0026 (6)	−0.0044 (6)	−0.0016 (6)
C1	0.022 (3)	0.018 (3)	0.015 (3)	−0.001 (2)	−0.002 (2)	−0.004 (2)
C2	0.037 (3)	0.018 (3)	0.018 (3)	−0.007 (2)	0.004 (2)	0.002 (2)
C3	0.040 (3)	0.026 (3)	0.020 (3)	−0.009 (3)	0.010 (3)	−0.003 (2)
C4	0.029 (3)	0.027 (3)	0.025 (3)	−0.003 (2)	0.010 (2)	−0.006 (2)
C5	0.027 (3)	0.020 (3)	0.031 (3)	−0.001 (2)	0.005 (2)	−0.003 (2)
C6	0.020 (3)	0.022 (3)	0.020 (3)	−0.004 (2)	0.003 (2)	−0.007 (2)
C7	0.017 (3)	0.019 (3)	0.018 (3)	0.004 (2)	−0.002 (2)	0.000 (2)
C8	0.021 (3)	0.014 (3)	0.024 (3)	0.000 (2)	0.004 (2)	−0.006 (2)
C9	0.029 (3)	0.027 (3)	0.022 (3)	0.003 (2)	0.001 (2)	0.004 (2)
C10	0.023 (3)	0.026 (3)	0.026 (3)	−0.006 (2)	0.008 (2)	−0.001 (2)
C11	0.024 (3)	0.033 (3)	0.029 (3)	−0.002 (2)	0.009 (2)	−0.006 (2)
C12	0.021 (3)	0.033 (3)	0.030 (3)	0.001 (2)	−0.003 (2)	−0.003 (2)
C13	0.021 (3)	0.021 (3)	0.022 (3)	−0.002 (2)	−0.002 (2)	−0.002 (2)
C14	0.018 (3)	0.019 (3)	0.023 (3)	0.006 (2)	−0.005 (2)	−0.002 (2)
C15	0.014 (3)	0.017 (3)	0.026 (3)	0.002 (2)	0.002 (2)	0.002 (2)
C16	0.026 (3)	0.021 (3)	0.019 (3)	0.002 (2)	−0.002 (2)	0.003 (2)
C17	0.029 (3)	0.021 (3)	0.015 (3)	0.004 (2)	−0.004 (2)	0.003 (2)
C18	0.024 (3)	0.022 (3)	0.018 (3)	−0.004 (2)	0.001 (2)	0.004 (2)

BR1—C4	1.900 (5)	C6—C7	1.433 (6)
BR2—C11	1.905 (5)	C7—H7	0.9300
CU1—O2	1.890 (3)	C8—C13	1.408 (6)
CU1—O1	1.915 (3)	C8—C9	1.415 (6)
CU1—N2	2.006 (4)	C9—C10	1.372 (6)
CU1—N1	2.018 (4)	C9—H9	0.9300
CU1—O1i	2.520 (3)	C10—C11	1.382 (7)
N1—C7	1.277 (5)	C10—H10	0.9300
N1—C15	1.480 (5)	C11—C12	1.362 (7)
N2—C14	1.284 (5)	C12—C13	1.413 (6)
N2—C17	1.471 (5)	C12—H12	0.9300
O1—C1	1.315 (5)	C13—C14	1.441 (6)
O2—C8	1.304 (5)	C14—H14	0.9300
S1—C16	1.808 (5)	C15—C16	1.511 (6)
S1—S2	2.0435 (17)	C15—H15A	0.9700
S2—C18ii	1.832 (5)	C15—H15B	0.9700
C1—C2	1.410 (6)	C16—H16A	0.9700
C1—C6	1.415 (6)	C16—H16B	0.9700
C2—C3	1.371 (6)	C17—C18	1.517 (6)
C2—H2	0.9300	C17—H17A	0.9700
C3—C4	1.403 (7)	C17—H17B	0.9700
C3—H3	0.9300	C18—S2ii	1.832 (5)
C4—C5	1.369 (7)	C18—H18A	0.9700
C5—C6	1.407 (6)	C18—H18B	0.9700
C5—H5	0.9300
O2—CU1—O1	170.63 (14)	C13—C8—C9	117.8 (4)
O2—CU1—N2	92.36 (15)	C10—C9—C8	121.4 (5)
O1—CU1—N2	91.68 (14)	C10—C9—H9	119.3
O2—CU1—N1	87.85 (14)	C8—C9—H9	119.3
O1—CU1—N1	91.88 (14)	C9—C10—C11	119.7 (5)
N2—CU1—N1	156.01 (14)	C9—C10—H10	120.1
O2—CU1—O1i	92.59 (12)	C11—C10—H10	120.1
O1—CU1—O1i	78.91 (12)	C12—C11—C10	121.2 (5)
N2—CU1—O1i	90.61 (12)	C12—C11—BR2	120.0 (4)
N1—CU1—O1i	113.35 (13)	C10—C11—BR2	118.8 (4)
C7—N1—C15	115.8 (4)	C11—C12—C13	120.2 (5)
C7—N1—CU1	122.7 (3)	C11—C12—H12	119.9
C15—N1—CU1	121.2 (3)	C13—C12—H12	119.9
C14—N2—C17	116.0 (4)	C8—C13—C12	119.7 (4)
C14—N2—CU1	123.6 (3)	C8—C13—C14	122.2 (4)
C17—N2—CU1	120.2 (3)	C12—C13—C14	117.9 (4)
C1—O1—CU1	127.1 (3)	N2—C14—C13	127.6 (4)
C8—O2—CU1	129.2 (3)	N2—C14—H14	116.2
C16—S1—S2	103.67 (16)	C13—C14—H14	116.2
C18ii—S2—S1	101.41 (16)	N1—C15—C16	110.9 (4)
O1—C1—C2	119.0 (4)	N1—C15—H15A	109.5
O1—C1—C6	123.5 (4)	C16—C15—H15A	109.5
C2—C1—C6	117.5 (4)	N1—C15—H15B	109.5
C3—C2—C1	121.8 (5)	C16—C15—H15B	109.5
C3—C2—H2	119.1	H15A—C15—H15B	108.0
C1—C2—H2	119.1	C15—C16—S1	113.1 (3)
C2—C3—C4	120.0 (4)	C15—C16—H16A	109.0
C2—C3—H3	120.0	S1—C16—H16A	109.0
C4—C3—H3	120.0	C15—C16—H16B	109.0
C5—C4—C3	119.9 (5)	S1—C16—H16B	109.0
C5—C4—BR1	119.9 (4)	H16A—C16—H16B	107.8
C3—C4—BR1	120.2 (4)	N2—C17—C18	113.8 (4)
C4—C5—C6	120.7 (5)	N2—C17—H17A	108.8
C4—C5—H5	119.7	C18—C17—H17A	108.8
C6—C5—H5	119.7	N2—C17—H17B	108.8
C5—C6—C1	120.1 (4)	C18—C17—H17B	108.8
C5—C6—C7	117.3 (4)	H17A—C17—H17B	107.7
C1—C6—C7	122.7 (4)	C17—C18—S2ii	113.1 (3)
N1—C7—C6	128.2 (4)	C17—C18—H18A	109.0
N1—C7—H7	115.9	S2ii—C18—H18A	109.0
C6—C7—H7	115.9	C17—C18—H18B	109.0
O2—C8—C13	124.2 (4)	S2ii—C18—H18B	109.0
O2—C8—C9	118.0 (4)	H18A—C18—H18B	107.8