1,8,14,20-Tetra­oxa-11,23-dithia­tricyclo­[21.3.0.0^9,13]hexa­cosa-9,12,21,24-tetra­ene

Mol­ecules of the title compound, C₂₀H₂₈O₄S₂, the first compound with a tetra­oxacyclo­hexa­cosane ring to be structurally characterized, lie on crystallographic centres of inversion, but have approximate C_2h mol­ecular symmetry. The parallel thio­phene rings are almost exactly planar; the overall conformation of the mol­ecule is chair-like. The mol­ecules have voids that could, in principle, accommodate small guest mol­ecules, although in the crystal structure access to these voids is blocked by neighbouring mol­ecules.

S1. Comment

Since their discovery in 1977 (Shirakawa et al., 1977), conjugated polymers have played an important role in modern science. Among the conjugated polymers studied to date, alkoxy- and dialkoxypolythiophenes (Skompska et al., 2005), and especially ethylenedioxythiophene (EDOT), have proved to be the most interesting among these materials (Groenendal et al., 2003; Ronali et al., 2005). Owing to several distinct advantages, polyethylenedioxythiophene (PEDOT) has rapidly acquired a prominent position among conducting polymers. A unique combination of moderate band gap and low oxidation potential confers on PEDOT an exceptional stability of the oxidized charged state, which furthermore exhibits high conductivity and good optical transparency in the visible spectroscopic region (Jonas & Schrader, 1991). To date, a large family of poly(alkylenedioxythiophenes), and therefore alkylenedioxythiophenes themselves, have been synthesized in order to elucidate the structure–property relationships in these materials (Kumar et al., 1998).

There are only 38 fragments of 3,4-oxo-substituted thiophenes in the Cambridge Structural Database (CSD, Version?; Allen, 2002); of these, 30 contain the 3,4-ethylenedioxythienyl group. Only two structures have the longer oxo-chains: 3,4-bis(hexadecyloxy)thiophene (CSD refcode ABUQET) and a dithiaporphyrin derivative, 2,3,12,13-tetrabutoxy-5,10,15,20-tetraphenyl-21,23-dithiaporphyrin (Agarwal et al., 2002). The crystal structure of the title compound, (I), is the first example of a molecule with two thiophene moieties connected by long chains. Surprisingly, it is also the first crystal structure of a molecule that possesses a tetraoxacyclohexacosane ring.

The molecule of (I) is symmetrical (Fig. 1a) and lies on a centre of inversion in space group Pbca. Moreover, there are two other approximate symmetry elements, namely a twofold axis through the midpoints of the C9—C10 and C9ⁱ—C10ⁱ bonds [symmetry code (i) −x, 2 − y, 1 − z], and a mirror plane perpendicular to this axis and containing the S atoms and the midpoints of the C3—C4 and C3ⁱ—C4ⁱ bonds. Thus, the overall symmetry of the molecule is closest to C_2h.

The molecular dimensions are typical (Table 1). The five-membered thiophene ring is planar to within experimental error [maximum deviation from the least squares plane is 0.003 (1) Å For which atom?]. Also, the deviations of the O atoms from this plane are almost negligible [O—C—C—O torsion angle 0.2 (3)°]. The conformation of the eight-membered chain can be analyzed in terms of its torsion angles (Table 1) and can be described as a-sc-a-a-a-sc-a. This conformation results in a chair-like overall conformation of the molecule (Fig. 1b).

The molecule has a void that, in principle, could accommodate small guest molecules [diagonal O···O distances across the void are 6.702 (3) and 6.754 (3) Å; Fig. 2]. However, in reality, neighbouring molecules completely block access to this void.

Only very weak intermolecular C—H···S interactions can be found in the crystal structure of (I) (H···S distances of ca 3.1 Å and C—H···S angles close to 160°). Therefore, van der Waals forces seem to be responsible for the crystal packing.

S2. Experimental

The synthesis of the title compound was reported by Czardybon et al. (2003). Crystals for X-ray data collection were grown from a methanol solution.

Computing details

Data collection: KM-4 User's Guide (Kuma Diffraction, 1991); cell refinement: KM-4 User's Guide; data reduction: KM-4 User's Guide; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Stereochemical Workstation Operation Manual (Siemens, 1989); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. (a) A perspective view of the molecule of (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. (b) A side view of the molecule of (I), showing the chair-like conformation.
	Fig. 2. van der Waals sphere representation of (I).

1,8,14,20-Tetraoxa-11,23-dithiatricyclo[21.3.0.0^9,13]hexacosa- 9,12,21,24-tetraene

Crystal data

C20H28O4S2	F(000) = 848
Mr = 396.54	Dx = 1.260 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 73 reflections
a = 9.595 (2) Å	θ = 3.3–20.1°
b = 8.267 (2) Å	µ = 0.28 mm^−1
c = 26.350 (5) Å	T = 295 K
V = 2090.1 (8) Å^3	Block, colourless
Z = 4	0.6 × 0.4 × 0.3 mm

Data collection

Kuma KM-4 diffractometer	Rint = 0.000
Radiation source: fine-focus sealed tube	θmax = 25.1°, θmin = 2.6°
Graphite monochromator	h = 0→11
ω/2θ scans	k = 0→9
1845 measured reflections	l = −31→0
1845 independent reflections	2 standard reflections every 100 reflections
1125 reflections with I > 2σ(I)	intensity decay: 0.7%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.036	All H-atom parameters refined
wR(F^2) = 0.105	w = 1/[σ^2(Fo^2) + (0.0684P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.98	(Δ/σ)max = 0.001
1845 reflections	Δρmax = 0.27 e Å^−3
175 parameters	Δρmin = −0.21 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0208 (19)

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	0.08426 (7)	1.22216 (8)	0.73732 (2)	0.0656 (3)
C2	0.1251 (3)	1.0485 (3)	0.70430 (8)	0.0547 (6)
H2	0.191 (2)	0.975 (3)	0.7171 (9)	0.062 (7)*
C3	0.0558 (2)	1.0419 (2)	0.65948 (7)	0.0459 (5)
C4	−0.0317 (2)	1.1799 (2)	0.65102 (8)	0.0484 (5)
C5	−0.0266 (3)	1.2860 (3)	0.69010 (9)	0.0582 (6)
H5	−0.071 (3)	1.389 (3)	0.6924 (8)	0.067 (7)*
O6	0.06023 (15)	0.92543 (17)	0.62306 (5)	0.0524 (4)
C7	0.1369 (3)	0.7818 (3)	0.63569 (9)	0.0504 (5)
H7A	0.233 (3)	0.810 (3)	0.6403 (8)	0.058 (7)*
H7B	0.094 (2)	0.732 (3)	0.6640 (9)	0.056 (6)*
C8	0.1262 (2)	0.6703 (3)	0.59068 (8)	0.0488 (5)
H8A	0.153 (2)	0.562 (3)	0.6014 (7)	0.046 (5)*
H8B	0.032 (3)	0.663 (3)	0.5826 (7)	0.048 (6)*
C9	0.2117 (3)	0.7236 (3)	0.54524 (8)	0.0536 (5)
H9A	0.209 (2)	0.845 (3)	0.5437 (8)	0.065 (7)*
H9B	0.306 (3)	0.692 (3)	0.5493 (9)	0.069 (7)*
C10	0.1579 (2)	0.6637 (3)	0.49468 (8)	0.0496 (5)
H10A	0.132 (2)	0.549 (3)	0.4961 (8)	0.057 (6)*
H10B	0.072 (3)	0.710 (3)	0.4859 (9)	0.065 (7)*
C11	0.2591 (2)	0.6880 (3)	0.45107 (8)	0.0497 (5)
H11A	0.336 (2)	0.603 (3)	0.4533 (8)	0.055 (6)*
H11B	0.297 (2)	0.796 (3)	0.4528 (8)	0.048 (5)*
C12	0.1953 (3)	0.6754 (3)	0.39905 (9)	0.0533 (6)
H12A	0.142 (2)	0.580 (3)	0.3947 (9)	0.067 (7)*
H12B	0.265 (3)	0.678 (3)	0.3741 (9)	0.065 (7)*
O13	0.10513 (16)	0.81246 (17)	0.39278 (5)	0.0553 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0852 (5)	0.0734 (4)	0.0383 (3)	0.0022 (3)	0.0061 (3)	−0.0061 (3)
C2	0.0622 (13)	0.0608 (14)	0.0412 (12)	0.0027 (12)	0.0068 (11)	0.0060 (10)
C3	0.0511 (11)	0.0463 (11)	0.0403 (10)	−0.0011 (9)	0.0104 (10)	0.0011 (9)
C4	0.0543 (11)	0.0473 (12)	0.0435 (11)	0.0003 (9)	0.0093 (10)	−0.0010 (9)
C5	0.0692 (14)	0.0557 (14)	0.0498 (12)	0.0086 (12)	0.0091 (11)	−0.0034 (11)
O6	0.0623 (9)	0.0481 (8)	0.0470 (8)	0.0122 (7)	−0.0035 (7)	−0.0044 (6)
C7	0.0546 (13)	0.0488 (12)	0.0478 (12)	0.0079 (11)	0.0042 (11)	0.0067 (10)
C8	0.0482 (13)	0.0422 (12)	0.0560 (13)	0.0018 (9)	0.0017 (10)	0.0040 (10)
C9	0.0548 (12)	0.0539 (12)	0.0521 (13)	−0.0046 (11)	0.0026 (11)	−0.0062 (10)
C10	0.0461 (12)	0.0475 (12)	0.0551 (13)	0.0030 (10)	0.0002 (10)	−0.0009 (10)
C11	0.0453 (11)	0.0481 (13)	0.0558 (13)	0.0054 (10)	0.0038 (10)	−0.0054 (10)
C12	0.0563 (13)	0.0477 (13)	0.0559 (13)	0.0092 (11)	0.0048 (12)	−0.0075 (10)
O13	0.0673 (9)	0.0493 (9)	0.0494 (8)	0.0145 (7)	−0.0059 (7)	−0.0072 (7)

Geometric parameters (Å, º)

S1—C5	1.720 (3)	C8—H8A	0.97 (2)
S1—C2	1.724 (3)	C8—H8B	0.93 (2)
C2—C3	1.356 (3)	C9—C10	1.512 (3)
C2—H2	0.94 (2)	C9—H9A	1.00 (2)
C3—O6	1.360 (2)	C9—H9B	0.94 (3)
C3—C4	1.434 (3)	C10—C11	1.518 (3)
C4—O13^i	1.353 (3)	C10—H10A	0.98 (2)
C4—C5	1.354 (3)	C10—H10B	0.94 (3)
C5—H5	0.95 (2)	C11—C12	1.505 (3)
O6—C7	1.435 (3)	C11—H11A	1.02 (2)
C7—C8	1.506 (3)	C11—H11B	0.97 (2)
C7—H7A	0.96 (3)	C12—O13	1.435 (3)
C7—H7B	0.95 (2)	C12—H12A	0.95 (3)
C8—C9	1.517 (3)	C12—H12B	0.93 (3)
C5—S1—C2	91.79 (11)	C10—C9—C8	114.54 (19)
C3—C2—S1	111.22 (18)	C10—C9—H9A	106.4 (13)
C3—C2—H2	128.0 (15)	C8—C9—H9A	107.8 (13)
S1—C2—H2	120.8 (15)	C10—C9—H9B	109.4 (15)
C2—C3—O6	128.9 (2)	C8—C9—H9B	110.2 (15)
C2—C3—C4	112.96 (19)	H9A—C9—H9B	108 (2)
O6—C3—C4	118.13 (18)	C9—C10—C11	113.88 (19)
O13^i—C4—C5	129.6 (2)	C9—C10—H10A	111.7 (12)
O13^i—C4—C3	118.34 (17)	C11—C10—H10A	108.5 (12)
C5—C4—C3	112.1 (2)	C9—C10—H10B	112.5 (15)
C4—C5—S1	111.92 (18)	C11—C10—H10B	108.7 (14)
C4—C5—H5	127.5 (14)	H10A—C10—H10B	101 (2)
S1—C5—H5	120.5 (14)	C12—C11—C10	114.8 (2)
C3—O6—C7	115.95 (16)	C12—C11—H11A	107.2 (12)
O6—C7—C8	106.81 (18)	C10—C11—H11A	109.1 (12)
O6—C7—H7A	108.8 (13)	C12—C11—H11B	105.1 (12)
C8—C7—H7A	108.2 (13)	C10—C11—H11B	109.1 (12)
O6—C7—H7B	108.5 (13)	H11A—C11—H11B	111.4 (16)
C8—C7—H7B	109.0 (13)	O13—C12—C11	107.20 (17)
H7A—C7—H7B	115.2 (19)	O13—C12—H12A	108.4 (15)
C7—C8—C9	114.01 (19)	C11—C12—H12A	112.8 (14)
C7—C8—H8A	108.4 (11)	O13—C12—H12B	109.1 (14)
C9—C8—H8A	110.6 (11)	C11—C12—H12B	110.5 (14)
C7—C8—H8B	106.6 (13)	H12A—C12—H12B	109 (2)
C9—C8—H8B	111.2 (13)	C4^i—O13—C12	116.68 (16)
H8A—C8—H8B	105.6 (18)
C5—S1—C2—C3	−0.17 (18)	C2—C3—O6—C7	7.2 (3)
S1—C2—C3—O6	179.90 (17)	C4—C3—O6—C7	−173.32 (18)
S1—C2—C3—C4	0.4 (2)	C3—O6—C7—C8	179.25 (18)
C2—C3—C4—O13^i	179.35 (18)	O6—C7—C8—C9	72.4 (3)
O6—C3—C4—O13^i	−0.2 (3)	C7—C8—C9—C10	−154.3 (2)
C2—C3—C4—C5	−0.6 (3)	C8—C9—C10—C11	−168.1 (2)
O6—C3—C4—C5	179.91 (19)	C9—C10—C11—C12	−163.08 (19)
O13^i—C4—C5—S1	−179.47 (17)	C10—C11—C12—O13	68.5 (3)
C3—C4—C5—S1	0.4 (2)	C11—C12—O13—C4^i	−176.95 (18)
C2—S1—C5—C4	−0.15 (19)

Symmetry code: (i) −x, −y+2, −z+1.