Synthesis and crystal structure of (E)-1,2-bis-[2-(methyl-sulfan-yl)phen-yl]diazene.

The title compound, C14H14N2S2, was obtained by transmetallation of 2,2'-bis-(tri-methyl-stann-yl)azo-benzene with methyl lithium, and subsequent quenching with dimethyl di-sulfide. The asymmetric unit comprises two half-mol-ecules, the other halves being completed by inversion symmetry at the midpoint of the azo group. The two mol-ecules show only slight differences with respect to N=N, S-N and aromatic C=C bonds or angles. Hirshfeld surface analysis reveals that except for one weak H⋯S inter-action, inter-molecular inter-actions are dominated by van der Waals forces only. © Hoffmann et al. 2019.

Chemical context

The mol­ecular switch azo­benzene can undergo isomerization from its thermodynamically stable trans form to the metastable cis form using external stimuli such as light, temperature or pressure. Azo­benzenes are common motifs in dyes because of their high thermal and photochemical stability (Yesodha et al., 2004 ▸; Lagrasta et al., 1997 ▸). We recently presented methods to substitute azo­benzenes in the ortho, meta and para-positions with tri­methyl­tin as a novel functionalization method, giving rise to a dual tin–lithium exchange (Strüben et al., 2014 ▸, 2015 ▸; Hoffmann et al., 2019 ▸). In particular, we described the effect on the diortho-substitution on azo­benzenes with trimethyl-tetrels and the resulting effects on the switching properties (Hoffmann et al., 2019 ▸). In this context, we present here a novel diortho-substituted azo­benzene, (C7H7NS)2, (I), bearing two methyl­sulfide groups.

Structural commentary

The asymmetric unit of the title compound consists of two half-mol­ecules (Ia and Ib), the other halves being completed by application of inversion symmetry. The midpoints of the N=N bonds are located on inversion centres, resulting in a trans-configuration for the central N=N bonds (Fig. 1 ▸). As indicated by the C6A—C1A—N1A—N1A i and C6B—C1B—N1B—N1B ii [symmetry codes: (i) −x, 1 − y, −z; (ii) 1 − x, 1 − y, 1 − z] torsion angles of 13.2 (2) and −5.3 (2)°, respectively, in both mol­ecules the phenyl rings are twisted slightly with respect to the azo unit. A weak distortion is also found for the N1—C1—C2—S1 torsion angles of −3.06 (16)° for Ia and −2.06 (15)° for Ib. The N=N bond lengths differ marginally [1.255 (2) Å for Ia, 1.264 (2) Å for Ib], as do comparable C—C bonds. For example, the C1—C2 bond in Ia is at 1.408 (2) Å slightly shorter than Ib [1.415 (2) Å]. In comparison, this bond is longer than all other C—C distances in the ring because of repulsion of the nitro­gen and the sulfur atoms attached to C1 and C2, respectively. In both mol­ecules, the S⋯N distances [2.8625 (13) Å for Ia, 2.8761 (11) Å for Ib] are too long to be considered as attractive inter­actions. Fig. 2 ▸ represents an overlay plot of the two mol­ecules, showing there are only slight conformational differences.

Figure 1

Mol­ecular structures (Ia left, Ib right) of the title compound with labelling and displacement ellipsoids drawn at the 50% probability level. [Symmetry codes: (i) x, 1 − y, − z; (ii) 1 − x, 1 − y, 1 − z.]

Figure 2

Overlay presentation of mol­ecules Ia and Ib.

Supra­molecular features and Hirshfeld surface analysis

The packing of Ia and Ib in the crystal is shown in Fig. 3 ▸. Despite the presence of phenyl rings and a parallel arrangement of the mol­ecules, only weak offset π–π inter­actions are observed; the shortest centroid-to-centroid distance is Cg2⋯Cg2(1 − x, 1 − y, −z) = 3.7525 (8) Å with a slippage of 1.422 Å. To further investigate the inter­molecular inter­actions, Hirshfeld surfaces (Hirshfeld, 1977 ▸) and fingerprint plots were generated for both mol­ecules using CrystalExplorer17.5 (McKinnon et al., 2004 ▸). Hirshfeld surface analysis depicts inter­molecular inter­actions by different colors, representing short or long contacts and further the relative strength of the inter­action. The generated Hirshfeld surfaces mapped over d norm and the shape index are shown in Fig. 4 ▸ for Ia and in Fig. 5 ▸ for Ib. Whereas in Ia a significant inter­molecular inter­action is not apparent, characteristic red spots near S1B and H5B indicate weak S⋯H inter­actions in Ib. The respective supra­molecular arrangement is shown in Fig. 6 ▸. The sulfur atom S1B inter­acts with a phenyl proton (H4B) of another mol­ecule of Ib (S⋯H distance = 2.811 Å). The two-dimensional fingerprint plots for mol­ecule Ib for qu­anti­fication of the contributions of each type of non-covalent inter­action to the Hirshfeld surface (McKinnon et al., 2007 ▸) are given in Fig. 7 ▸. The packing is dominated by H⋯H contacts, representing van der Waals inter­actions (44.5% contribution to the surface), followed by C⋯H and S⋯H inter­actions, which contribute with 24.0% and 18.1%, respectively. The contributions of the N⋯H (8.6%) and C⋯C (4.8%) inter­actions are less significant.

Figure 3

Crystal packing in a view along the b axis. To distinguish the different mol­ecules, all sulfur atoms within the unit cell are labelled.

Figure 4

Hirshfeld surface of Ia mapped with d norm (top) and shape index (bottom), displaying no significant inter­molecular inter­actions.

Figure 5

Hirshfeld surface of Ib mapped with d norm (top) and shape index (bottom) with indication of an S⋯H inter­action.

Figure 6

Hirshfeld surface of Ib mapped with d norm (left) and shape index (right), together with the inter­action of a neighbouring mol­ecule.

Figure 7

Two-dimensional fingerprint plots for Ib, delineated into H⋯H, C⋯H, S⋯H, N⋯H, C⋯C inter­actions.

Database survey

A search of the Cambridge Structural Database (CSD version 5.4.0; update August 2019; Groom et al., 2016 ▸) revealed no azo­benzene-based structures that contain methyl thio­ethers. However, some general ortho-substituted azo­benzenes have been deposited (Yamamura et al., 2008 ▸; Kano et al., 2001 ▸; Hoffmann et al., 2019 ▸). Additionally, some diortho-substituted thio­azoxybenzenes were reported previously (Szczygelska-Tao et al., 1999 ▸; Kertmen et al., 2013 ▸). For the structure of an azo­benzene compound with an inversion centre at the N=N bond, see: Bohle et al. (2007 ▸).

Synthesis and crystallization

The synthesis of 2,2′-bis(tri­methyl­stann­yl)azo­benzene was recently described (Hoffmann et al., 2019 ▸). For further details of a similar transmetallation of a stannylated azo­benzene, see: Strüben et al. (2015 ▸). Dimethyl di­sulfide (99%) was purchased from Acros Organics and was used without further purification. Methyl lithium (1.88 M in diethyl ether, titrated against 2,2′-bi­pyridine) was purchased from Acros Organics. THF was purchased from VWR and was dried and degassed with a solvent purification system by Inert Technology.

2,2′-bis­(Methyl­thio)­azo­benzene

In an inert reaction tube, 2,2-bis(tri­methyl­stann­yl)azo­benzene (200 mg, 0.39 mmol) was dissolved under Schlenk conditions in THF (12.5 ml) and cooled to 195 K. Then MeLi (1.88 M in diethyl ether, 0.63 ml, 1.18 mmol) was added within 5 min and after 1.5 h at this temperature, dimethyl di­sulfide (0.35 ml, 3.94 mmol) was added in one ration. The reaction mixture was warmed to 298 K over 14 h and the solvent was removed under reduced pressure. The obtained orange solid was purified in a silica column (Merck, 0.015–0.40 mm) with a gradient of eluents from n-pentane to di­chloro­methane giving dark-orange crystals (31 mg, 0.11 mmol; yield 29%). Single crystals suitable for X-ray analysis were obtained by slow evaporation from a saturated n-heptane solution.

(500 MHz, CDCl3): δ = 7.76 (dd, 3 J = 8.1 Hz, 4 J = 1.4 Hz, 2H, H6), 7.40 (td, 3 J = 8.0, 7.3 Hz, 4 J = 1.4 Hz, 2H, H4), 7.32 (dd, 3 J = 8.0 Hz, 4 J = 1.1 Hz, 2H, H3), 7.20 (td, 3 J = 8.1, 7.3Hz, 4 J = 1.1 Hz, 2H, H5), 2.53 (s, 6H, H7) ppm.

(125 MHz, CDCl3): δ = 149.08 (C1), 141.00 (C2), 131.56 (C4), 124.81 (C3), 124.75 (C5), 118.02 (C6), 15.02 (C7) ppm.

HRMS (EI, 70 eV, MAT95, direct): m/z: calculated for C14H14N2S2 + 274.05929 found 274.05944.

MS (EI): m/z 273.9 (5%) [M]+, 258.9 (100%) [M − CH3]+, 243.9 (5%) [M − C2H6]+, 107.9 (13%) [M − C8H10N2S]+.

IR (ATR): ν = 3059 (w), 2986 (w), 2961 (w), 2918 (w), 2852 (w), 1575 (m), 1561 (w), 1457 (m), 1433 (s), 1298 (w), 1249 (w), 1217 (m), 1162 (m), 1065 (s), 1035 (m), 951 (m), 863 (w), 803 (w), 761 (s), 726 (s), 674 (s) cm−1.

M.p.: 429 K

: (n-penta­ne: di­chloro­methane 3:1): 0.55.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1 ▸. All H atoms were positioned geometrically and refined using a riding model: C—H = 0.95–0.98 Å with U iso(H) = 1.5U eq (C-meth­yl) and 1.2U eq(C) (C-phen­yl).

Table 1

Experimental details

Crystal data
Chemical formula	C14H14N2S2
M r	274.39
Crystal system, space group	Monoclinic, P21/c
Temperature (K)	100
a, b, c (Å)	13.0656 (5), 12.1787 (4), 8.3471 (3)
β (°)	96.154 (1)
V (Å3)	1320.55 (8)
Z	4
Radiation type	Mo Kα
μ (mm−1)	0.39
Crystal size (mm)	0.21 × 0.18 × 0.17
Data collection
Diffractometer	Bruker D8 Venture CMOS
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 ▸)
T min, T max	0.580, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	21000, 3292, 2842
R int	0.065
(sin θ/λ)max (Å−1)	0.668
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.034, 0.089, 1.04
No. of reflections	3292
No. of parameters	165
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.44, −0.38

Computer programs: APEX3 and SAINT (Bruker, 2016 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL (Sheldrick, 2015b ▸) and OLEX2 (Dolomanov et al., 2009 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989019014592/wm5522sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989019014592/wm5522Isup2.hkl

CCDC references: 1961741, 1961741

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

C14H14N2S2	F(000) = 576
Mr = 274.39	Dx = 1.380 Mg m−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 13.0656 (5) Å	Cell parameters from 9874 reflections
b = 12.1787 (4) Å	θ = 2.3–28.3°
c = 8.3471 (3) Å	µ = 0.39 mm−1
β = 96.154 (1)°	T = 100 K
V = 1320.55 (8) Å3	Block, dark orange
Z = 4	0.21 × 0.18 × 0.17 mm

Bruker D8 Venture CMOS diffractometer	3292 independent reflections
Radiation source: microfocus sealed X-ray tube, Incoatec Iµs	2842 reflections with I > 2σ(I)
Mirror optics monochromator	Rint = 0.065
Detector resolution: 7.9 pixels mm-1	θmax = 28.3°, θmin = 2.3°
ω and φ scans	h = −17→17
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	k = −16→16
Tmin = 0.580, Tmax = 0.746	l = −11→10
21000 measured reflections

Refinement on F2	Primary atom site location: dual
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.034	H-atom parameters constrained
wR(F2) = 0.089	w = 1/[σ2(Fo2) + (0.0401P)2 + 0.6716P] where P = (Fo2 + 2Fc2)/3
S = 1.03	(Δ/σ)max < 0.001
3292 reflections	Δρmax = 0.44 e Å−3
165 parameters	Δρmin = −0.38 e Å−3
0 restraints

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
S1A	0.03738 (3)	0.22038 (3)	0.07109 (4)	0.01750 (10)
N1A	0.00557 (9)	0.45111 (10)	0.02308 (14)	0.0144 (2)
C1A	0.09596 (10)	0.43239 (11)	0.13020 (16)	0.0133 (3)
C2A	0.12139 (10)	0.32133 (11)	0.15962 (16)	0.0136 (3)
C3A	0.21227 (10)	0.29785 (12)	0.25937 (17)	0.0163 (3)
H3A	0.232873	0.223733	0.278065	0.020*
C4A	0.27191 (10)	0.38209 (12)	0.33050 (17)	0.0175 (3)
H4A	0.333363	0.364884	0.397179	0.021*
C5A	0.24372 (10)	0.49160 (12)	0.30637 (17)	0.0170 (3)
H5A	0.284385	0.548538	0.358432	0.020*
C6A	0.15556 (10)	0.51642 (12)	0.20540 (16)	0.0153 (3)
H6A	0.135717	0.590824	0.187411	0.018*
C7A	0.09736 (12)	0.09607 (12)	0.15119 (19)	0.0212 (3)
H7AA	0.108296	0.100874	0.268985	0.032*
H7AB	0.163749	0.086347	0.108405	0.032*
H7AC	0.052690	0.033332	0.119805	0.032*
S1B	0.68646 (3)	0.36826 (3)	0.29648 (4)	0.01522 (10)
N1B	0.53057 (8)	0.47643 (9)	0.45728 (13)	0.0111 (2)
C1B	0.54712 (9)	0.53356 (10)	0.31394 (15)	0.0107 (2)
C2B	0.62096 (9)	0.48706 (11)	0.22188 (15)	0.0109 (2)
C3B	0.63884 (10)	0.53770 (11)	0.07713 (16)	0.0135 (3)
H3B	0.688084	0.507481	0.013715	0.016*
C4B	0.58521 (10)	0.63170 (11)	0.02550 (16)	0.0149 (3)
H4B	0.597271	0.664586	−0.073966	0.018*
C5B	0.51371 (10)	0.67861 (11)	0.11794 (16)	0.0141 (3)
H5B	0.478373	0.743923	0.082900	0.017*
C6B	0.49478 (10)	0.62917 (11)	0.26090 (16)	0.0121 (3)
H6B	0.445749	0.660464	0.323699	0.015*
C7B	0.77056 (12)	0.33890 (13)	0.1449 (2)	0.0230 (3)
H7BA	0.729477	0.327171	0.041043	0.035*
H7BB	0.810613	0.272618	0.174984	0.035*
H7BC	0.817418	0.400922	0.136102	0.035*

	U11	U22	U33	U12	U13	U23
S1A	0.01446 (17)	0.01894 (19)	0.01851 (19)	−0.00155 (13)	−0.00094 (13)	−0.00187 (13)
N1A	0.0110 (5)	0.0196 (6)	0.0125 (5)	0.0009 (4)	0.0008 (4)	−0.0003 (4)
C1A	0.0098 (6)	0.0203 (7)	0.0100 (6)	−0.0002 (5)	0.0022 (5)	0.0005 (5)
C2A	0.0102 (6)	0.0199 (7)	0.0111 (6)	−0.0010 (5)	0.0032 (5)	−0.0020 (5)
C3A	0.0129 (6)	0.0205 (7)	0.0155 (7)	0.0018 (5)	0.0011 (5)	0.0019 (5)
C4A	0.0112 (6)	0.0267 (7)	0.0139 (6)	0.0008 (5)	−0.0013 (5)	0.0017 (6)
C5A	0.0136 (6)	0.0250 (7)	0.0124 (6)	−0.0033 (5)	0.0013 (5)	−0.0021 (5)
C6A	0.0141 (6)	0.0194 (7)	0.0128 (6)	−0.0005 (5)	0.0029 (5)	0.0000 (5)
C7A	0.0238 (7)	0.0182 (7)	0.0215 (7)	−0.0003 (6)	0.0026 (6)	0.0015 (6)
S1B	0.01542 (17)	0.01406 (17)	0.01718 (18)	0.00275 (12)	0.00642 (13)	0.00248 (12)
N1B	0.0103 (5)	0.0140 (5)	0.0090 (5)	−0.0019 (4)	0.0012 (4)	−0.0012 (4)
C1B	0.0097 (5)	0.0135 (6)	0.0088 (6)	−0.0028 (5)	0.0008 (5)	−0.0014 (5)
C2B	0.0096 (5)	0.0112 (6)	0.0115 (6)	−0.0013 (5)	0.0001 (5)	−0.0013 (5)
C3B	0.0124 (6)	0.0176 (6)	0.0111 (6)	−0.0014 (5)	0.0042 (5)	−0.0018 (5)
C4B	0.0160 (6)	0.0180 (7)	0.0108 (6)	−0.0030 (5)	0.0020 (5)	0.0019 (5)
C5B	0.0142 (6)	0.0146 (6)	0.0130 (6)	0.0002 (5)	0.0000 (5)	0.0011 (5)
C6B	0.0109 (6)	0.0148 (6)	0.0106 (6)	−0.0011 (5)	0.0011 (5)	−0.0020 (5)
C7B	0.0229 (7)	0.0210 (7)	0.0276 (8)	0.0061 (6)	0.0144 (6)	0.0013 (6)

S1A—C2A	1.7574 (14)	S1B—C2B	1.7605 (13)
S1A—C7A	1.8002 (15)	S1B—C7B	1.7983 (15)
N1A—N1Ai	1.255 (2)	N1B—N1Bii	1.264 (2)
N1A—C1A	1.4211 (17)	N1B—C1B	1.4205 (16)
C1A—C2A	1.4080 (19)	C1B—C2B	1.4145 (18)
C1A—C6A	1.3940 (19)	C1B—C6B	1.3981 (18)
C2A—C3A	1.4046 (18)	C2B—C3B	1.3983 (18)
C3A—H3A	0.9500	C3B—H3B	0.9500
C3A—C4A	1.383 (2)	C3B—C4B	1.3866 (19)
C4A—H4A	0.9500	C4B—H4B	0.9500
C4A—C5A	1.393 (2)	C4B—C5B	1.3961 (19)
C5A—H5A	0.9500	C5B—H5B	0.9500
C5A—C6A	1.3857 (19)	C5B—C6B	1.3824 (19)
C6A—H6A	0.9500	C6B—H6B	0.9500
C7A—H7AA	0.9800	C7B—H7BA	0.9800
C7A—H7AB	0.9800	C7B—H7BB	0.9800
C7A—H7AC	0.9800	C7B—H7BC	0.9800
C2A—S1A—C7A	101.82 (7)	C2B—S1B—C7B	103.00 (7)
N1Ai—N1A—C1A	113.98 (14)	N1Bii—N1B—C1B	114.53 (14)
C2A—C1A—N1A	115.37 (12)	C2B—C1B—N1B	115.83 (11)
C6A—C1A—N1A	123.50 (13)	C6B—C1B—N1B	124.14 (11)
C6A—C1A—C2A	121.11 (12)	C6B—C1B—C2B	120.02 (12)
C1A—C2A—S1A	118.27 (10)	C1B—C2B—S1B	118.09 (10)
C3A—C2A—S1A	123.84 (11)	C3B—C2B—S1B	123.24 (10)
C3A—C2A—C1A	117.89 (12)	C3B—C2B—C1B	118.67 (12)
C2A—C3A—H3A	119.8	C2B—C3B—H3B	119.8
C4A—C3A—C2A	120.33 (13)	C4B—C3B—C2B	120.46 (12)
C4A—C3A—H3A	119.8	C4B—C3B—H3B	119.8
C3A—C4A—H4A	119.3	C3B—C4B—H4B	119.6
C3A—C4A—C5A	121.35 (13)	C3B—C4B—C5B	120.79 (12)
C5A—C4A—H4A	119.3	C5B—C4B—H4B	119.6
C4A—C5A—H5A	120.4	C4B—C5B—H5B	120.3
C6A—C5A—C4A	119.12 (13)	C6B—C5B—C4B	119.42 (13)
C6A—C5A—H5A	120.4	C6B—C5B—H5B	120.3
C1A—C6A—H6A	119.9	C1B—C6B—H6B	119.7
C5A—C6A—C1A	120.10 (13)	C5B—C6B—C1B	120.63 (12)
C5A—C6A—H6A	119.9	C5B—C6B—H6B	119.7
S1A—C7A—H7AA	109.5	S1B—C7B—H7BA	109.5
S1A—C7A—H7AB	109.5	S1B—C7B—H7BB	109.5
S1A—C7A—H7AC	109.5	S1B—C7B—H7BC	109.5
H7AA—C7A—H7AB	109.5	H7BA—C7B—H7BB	109.5
H7AA—C7A—H7AC	109.5	H7BA—C7B—H7BC	109.5
H7AB—C7A—H7AC	109.5	H7BB—C7B—H7BC	109.5
S1A—C2A—C3A—C4A	−177.02 (11)	S1B—C2B—C3B—C4B	−179.51 (10)
N1Ai—N1A—C1A—C2A	−168.19 (14)	N1Bii—N1B—C1B—C2B	175.48 (13)
N1Ai—N1A—C1A—C6A	13.2 (2)	N1Bii—N1B—C1B—C6B	−5.3 (2)
N1A—C1A—C2A—S1A	−3.06 (16)	N1B—C1B—C2B—S1B	−2.06 (15)
N1A—C1A—C2A—C3A	177.45 (12)	N1B—C1B—C2B—C3B	178.30 (11)
N1A—C1A—C6A—C5A	−178.94 (12)	N1B—C1B—C6B—C5B	−178.56 (12)
C1A—C2A—C3A—C4A	2.4 (2)	C1B—C2B—C3B—C4B	0.11 (19)
C2A—C1A—C6A—C5A	2.5 (2)	C2B—C1B—C6B—C5B	0.61 (19)
C2A—C3A—C4A—C5A	0.3 (2)	C2B—C3B—C4B—C5B	1.1 (2)
C3A—C4A—C5A—C6A	−1.8 (2)	C3B—C4B—C5B—C6B	−1.4 (2)
C4A—C5A—C6A—C1A	0.4 (2)	C4B—C5B—C6B—C1B	0.54 (19)
C6A—C1A—C2A—S1A	175.63 (10)	C6B—C1B—C2B—S1B	178.71 (10)
C6A—C1A—C2A—C3A	−3.86 (19)	C6B—C1B—C2B—C3B	−0.94 (18)
C7A—S1A—C2A—C1A	−176.89 (11)	C7B—S1B—C2B—C1B	−179.91 (10)
C7A—S1A—C2A—C3A	2.57 (13)	C7B—S1B—C2B—C3B	−0.28 (13)