2,5-Di-2-thienyl­thia­zolo­[4,5-d]­thia­zole

The mol­ecules of the title compound, C₁₂H₆N₂S₄, lie on centres of symmetry. The thio­phene and thia­zole rings are almost planar and their planes make a dihedral angle of 1.68 (8)°. In the crystal structure, there is a relatively short intermolecular S...S contact distance of 3.5786 (9) Å.

S1. Comment

The strong need for new ecological energy sources has resulted in a growing interest in new organic semiconducting materials, for example, those based on thiophene derivatives (for a review, see Nalva, 1997). The electric conductivity and the band-gap (Eg) are strongly dependent on some structural parameters, including the geometry of a monomer molecule. Therefore, a detailed knowledge of the geometrical parameters (such as the planarity of the molecules, their mutual arrangenment, and intra- and intermolecular interactions) and electronic properties (e.g. the charge-density distribution) is crucial for a rational design of new materials. We performed an X-ray structural analysis of 2,5-Di-2-thienylthiazolo[4,5-d]thiazole, (I), a simple model compound that could be used for electro-optically active materials. The X-ray data could then be used as the starting model for semi-empirical or ab initio calculations for molecular engineering.

There is a surprisingly small number of similar compounds in the Cambridge Structural Database (CSD; Allen, 2002); in the May 2002 release we found only three thiazolo[4,5-d]thiazoles and just one compound with the thieno–thiazole moiety. These findings further emphasize the need for detailed structural data.

The molecule of (I) lies on the center of symmetry in the space group P2₁/n. Crystals of all three thiazolo[4,5-d]thiazoles found in the CSD belong to crystal class C_{2 h} and contain two molecules per unit cell. All of these molecules lie on centres of symmetry in the crystals (Bossio et al., 1987; Bolognesi et al., 1987).

Both symmetry-independent rings in (I) are almost planar [maximum deviations are 0.0044 (8) Å for the thiophene ring and 0.0008 (7) Å for the thiazole ring], and the dihedral angle between the least-squares planes of these rings is 1.68 (8)°. The bond lengths and angles in the thiazole ring are similar to those found in thiazolo[5,4-d]thiazole (Bolognesi et al., 1987). Asymmetry of the S—C bond lengths in the thiazole ring is observed also in other thiazole derivatives, especially in cases where there is another ring condensed at the C4═C5 double bonds. The S1'—C2' bond length of 1.7605 (14) Å is typical of a single S—C bond, while the S1'—C4'(1 − x, 1 − y, −z) bond has considerable double-bond character and may therefore be involved in resonance (cf. Smith, 1969; Ekstrand & van der Helm, 1977; Bolognesi et al., 1987).

In the crystal structure, there are relatively short S1'···S1'(-x, 1 − y, −z) intermolecular contacts [3.5786 (9) Å] that link the molecules into infinite chains along the [100] direction. The angle between a vector connecting the S atoms and a normal to the plane of the thiazole ring is 35.8°. Such short contacts are quite common in divalent sulfur compounds. However, they are less frequently observed in thiazole derivatives. For all divalent sulfur compounds, intermolecular S···S contacts shorter than 3.6 Å are observed in 11.4% of cases, contacts shorter than 3.65 Å are observed in 13.4% of cases and contacts shorter than 3.7 Å are observed in 16.4% of cases. For compounds with sulfur in a cyclic environment, these values are even higher, the respective values being 12.2, 15.3 and 18.3%. For thiazole derivatives, the fraction of compounds that possess short S···S contacts is much smaller, viz. 4.2% for a 3.6 Å separation, 5.9% for a 3.65 Å separation and 8.2% for a 3.7 Å separation. Such short contacts are not found in any of three thiazolo[4,5-d]thiazole derivatives for which the crystal structures were reported.

The crystal packing is determined by the partial overlap of planar molecules (the distance between the mean planes of two molecules related by the center of symmetry is ca 3.6 Å) and, to some extent, by S···S contacts and weak C—H···S interactions (cf. Table 2).

S2. Experimental

The title compound was synthesized according to the procedure of Thomas (1970) by condensation of dithiooxodiamide with 2-formylthiophene. Colourless prismatic crystals were grown from a methanol solution by slow evaporation.

Computing details

Data collection: CrysAlis CCD (Kuma, 1999); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Kuma, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997).

Figures

Fig. 1. View (Siemens, 1989) of the chain of molecules of (I) connected by S···S contacts (dashed lines) and the atomic numbering. Displacement ellipsoids are drawn at the 50% probability level and H atoms are depicted as spheres of arbitrary radii. [Symmetry codes: (i) 1 − x, 1 − y, −z; (ii) −1 + x, y, z; (iii) −x, 1 − y, −z.]

2,5-Di-2-thienylthiazolo[4,5-d]thiazole

Crystal data

C12H6N2S4	F(000) = 312
Mr = 306.47	Dx = 1.655 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 6.0040 (12) Å	Cell parameters from 4325 reflections
b = 8.3580 (17) Å	θ = 4–22°
c = 12.270 (3) Å	µ = 0.75 mm^−1
β = 92.72 (3)°	T = 293 K
V = 615.0 (2) Å^3	Block, colourless
Z = 2	0.3 × 0.2 × 0.2 mm

Data collection

Kuma KM4CCD four-circle diffractometer	1475 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.024
Graphite monochromator	θmax = 29.0°, θmin = 4.1°
ω scans	h = −8→6
5376 measured reflections	k = −11→11
1574 independent reflections	l = −16→13

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.028	Hydrogen site location: difference Fourier map
wR(F^2) = 0.068	All H-atom parameters refined
S = 1.10	w = 1/[σ^2(Fo^2) + (0.0305P)^2 + 0.3939P] where P = (Fo^2 + 2Fc^2)/3
1574 reflections	(Δ/σ)max < 0.001
94 parameters	Δρmax = 0.37 e Å^−3
0 restraints	Δρmin = −0.29 e Å^−3

Special details

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
S1	0.61877 (6)	0.01323 (4)	0.19196 (3)	0.01726 (11)
C2	0.4041 (2)	0.10661 (16)	0.11773 (11)	0.0139 (3)
C3	0.2127 (2)	0.01461 (17)	0.11555 (11)	0.0169 (3)
H3	0.079 (3)	0.055 (3)	0.0842 (17)	0.031 (5)*
C4	0.2419 (3)	−0.13209 (18)	0.17292 (12)	0.0197 (3)
H4	0.127 (3)	−0.212 (3)	0.1803 (17)	0.034 (6)*
C5	0.4529 (3)	−0.14856 (17)	0.21816 (12)	0.0189 (3)
H5	0.513 (3)	−0.231 (2)	0.2630 (17)	0.030 (5)*
S1'	0.22016 (6)	0.35656 (4)	−0.00667 (3)	0.01680 (11)
C2'	0.4380 (2)	0.26208 (16)	0.06986 (11)	0.0138 (3)
N3'	0.62763 (19)	0.34238 (14)	0.08042 (10)	0.0155 (2)
C4'	0.6019 (2)	0.48388 (16)	0.02621 (11)	0.0142 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.01295 (17)	0.01639 (18)	0.02226 (19)	0.00036 (12)	−0.00119 (13)	0.00345 (12)
C2	0.0141 (6)	0.0153 (6)	0.0121 (6)	0.0006 (5)	−0.0002 (5)	−0.0009 (5)
C3	0.0143 (7)	0.0208 (7)	0.0153 (6)	−0.0022 (5)	−0.0019 (5)	0.0025 (5)
C4	0.0210 (7)	0.0207 (7)	0.0172 (6)	−0.0064 (5)	−0.0004 (5)	0.0013 (5)
C5	0.0211 (7)	0.0154 (6)	0.0202 (7)	−0.0004 (5)	0.0012 (5)	0.0031 (5)
S1'	0.01196 (17)	0.01626 (18)	0.02174 (18)	−0.00226 (12)	−0.00383 (12)	0.00402 (12)
C2'	0.0128 (6)	0.0159 (6)	0.0126 (6)	0.0008 (5)	−0.0006 (5)	−0.0002 (5)
N3'	0.0132 (5)	0.0161 (6)	0.0169 (6)	−0.0011 (4)	−0.0019 (4)	0.0010 (4)
C4'	0.0111 (6)	0.0155 (6)	0.0159 (6)	−0.0008 (5)	−0.0008 (5)	0.0005 (5)

Geometric parameters (Å, º)

S1—C5	1.7187 (15)	C5—H5	0.94 (2)
S1—C2	1.7287 (14)	S1'—C4'^i	1.7324 (14)
C2—C3	1.3820 (19)	S1'—C2'	1.7605 (14)
C2—C2'	1.4444 (19)	C2'—N3'	1.3226 (18)
C3—C4	1.421 (2)	N3'—C4'	1.3621 (17)
C3—H3	0.94 (2)	C4'—C4'^i	1.382 (3)
C4—C5	1.366 (2)	C4'—S1'^i	1.7324 (14)
C4—H4	0.97 (2)
C5—S1—C2	91.70 (7)	C4—C5—H5	129.3 (12)
C3—C2—C2'	128.75 (13)	S1—C5—H5	118.4 (12)
C3—C2—S1	110.95 (11)	C4'^i—S1'—C2'	88.38 (7)
C2'—C2—S1	120.29 (10)	N3'—C2'—C2	123.64 (12)
C2—C3—C4	112.80 (13)	N3'—C2'—S1'	116.03 (10)
C2—C3—H3	120.4 (13)	C2—C2'—S1'	120.32 (10)
C4—C3—H3	126.6 (13)	C2'—N3'—C4'	108.40 (12)
C5—C4—C3	112.27 (13)	N3'—C4'—C4'^i	118.29 (15)
C5—C4—H4	122.7 (12)	N3'—C4'—S1'^i	132.82 (10)
C3—C4—H4	125.0 (12)	C4'^i—C4'—S1'^i	108.89 (13)
C4—C5—S1	112.28 (11)
C5—S1—C2—C3	0.65 (11)	C3—C2—C2'—S1'	−2.0 (2)
C5—S1—C2—C2'	179.43 (11)	S1—C2—C2'—S1'	179.48 (7)
C2'—C2—C3—C4	−179.40 (13)	C4'^i—S1'—C2'—N3'	0.13 (11)
S1—C2—C3—C4	−0.76 (16)	C4'^i—S1'—C2'—C2	179.61 (12)
C2—C3—C4—C5	0.48 (19)	C2—C2'—N3'—C4'	−179.56 (12)
C3—C4—C5—S1	0.02 (17)	S1'—C2'—N3'—C4'	−0.10 (15)
C2—S1—C5—C4	−0.38 (12)	C2'—N3'—C4'—C4'^i	0.0 (2)
C3—C2—C2'—N3'	177.46 (14)	C2'—N3'—C4'—S1'^i	−179.87 (12)
S1—C2—C2'—N3'	−1.08 (19)

Symmetry code: (i) −x+1, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3···S1^ii	0.94 (2)	3.14 (2)	3.7298 (17)	122.9 (15)
C4—H4···S1′^iii	0.97 (2)	3.15 (2)	3.8523 (17)	130.7 (15)
C4—H4···S1^iv	0.97 (2)	3.18 (2)	4.0704 (17)	153.4 (16)
C5—H5···S1^v	0.94 (2)	3.10 (2)	3.9434 (17)	148.9 (16)

Symmetry codes: (ii) x−1, y, z; (iii) −x, −y, −z; (iv) −x+1/2, y−1/2, −z+1/2; (v) −x+3/2, y−1/2, −z+1/2.