Diethyl 2,5-bis­[(E)-2-furylmethyl­ene­amino]thio­phene-3,4-dicarboxyl­ate

Stéphane Dufresne; W G Skene

doi:10.1107/S1600536808006612

. 2008 Mar 14;64(Pt 4):o710. doi: 10.1107/S1600536808006612

Diethyl 2,5-bis[(E)-2-furylmethyleneamino]thiophene-3,4-dicarboxylate

Stéphane Dufresne ^a, W G Skene ^a,^*

PMCID: PMC2960980 PMID: 21202101

Abstract

The title compound, C₂₀H₁₈N₂O₆S, crystallizes as two independent molecules that are disposed about a pseudo-inversion center (1/2, 1/4, 1/8). The mean planes of the two terminal furyl rings are twisted with respect to the central thiophene ring by 7.33 (4) and 21.74 (5)° in one molecule, and by 6.91 (4) and 39.80 (6)° in the other.

Related literature

For general background, see: Dufresne et al. (2007 ▶). For related literature, see: Dufresne et al. (2006 ▶). For compounds crystallizing with two independent molecules in the space groups Pca2₁ and Pna2₁, disposed about a pseudo-inversion center, see: Marsh et al. (1998 ▶).

Experimental

Crystal data

C₂₀H₁₈N₂O₆S
M _r = 414.42
Orthorhombic,
a = 8.2540 (3) Å
b = 10.1578 (3) Å
c = 46.087 (2) Å
V = 3864.0 (2) Å³
Z = 8
Cu Kα radiation
μ = 1.85 mm⁻¹
T = 220 (2) K
0.28 × 0.23 × 0.14 mm

Data collection

Bruker SMART 2000 diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T _min = 0.640, T _max = 0.781
45562 measured reflections
7392 independent reflections
7164 reflections with I > 2σ(I)
R _int = 0.030

Refinement

R[F ² > 2σ(F ²)] = 0.032
wR(F ²) = 0.087
S = 1.03
7392 reflections
527 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.25 e Å⁻³
Δρ_min = −0.21 e Å⁻³
Absolute structure: Flack (1983 ▶), 3551 Friedel pairs
Flack parameter: 0.021 (10)

Data collection: SMART (Bruker, 1999 ▶); cell refinement: SAINT (Bruker, 1999 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: UdMX (Marris, 2004 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808006612/ng2429sup1.cif

e-64-0o710-sup1.cif^{(33KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808006612/ng2429Isup2.hkl

e-64-0o710-Isup2.hkl^{(361.7KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

The authors acknowledge financial support from the Natural Sciences and Engineering Research Council Canada, the Centre for Self-Assembled Chemical Structures, and Canada Foundation for Innovation. SD thanks the Université de Montréal for a graduate scholarship.

supplementary crystallographic information

Comment

The molecule (I) was prepared as a result of our ongoing research of conjugated azomethines for electronic devices. The crystal structure of (I) confirmed that the compound consisted of a central thiophene capped by two terminal furans that are connected by two azomethine bonds. Even though two isomers are possible, only the more stable E isomer was confirmed by the resolved structure. The chemical structure occurs eight times in the Pca2₁ lattice as seen in Figure 2 with two different molecules of (I) per cell disposed near a false inversion center at 1/2, 1/4, 1/8. (Marsh et al., 1998) Neither solvent nor counter-ions were found in the closed-packed stacking.

A major point of interest is the azomethine bond. The measured imine bond lengths for C14—C15, N11—C15 and N11—C16 are 1.429 (2), 1.287 (2) and 1.375 (2) Å, respectively. The bond distances are comparable to an all thiophene bisazomethine analogue (Dufresne et al., 2006) whose analogous lengths are 1.441 (4), 1.272 (3) and 1.388 (3) Å.

The mean plane angles described by all three heterocycles of (I) are not entirely coplanar. The mean plane angles of the terminal furans are twisted 7.33 (4)° and 21.74 (5)° for one molecule of (I) with respect to the central thiohene. Similarly, the mean planes are twisted by 6.91 (4)° and 39.80 (6)° for the second molecule found in the lattice. Meanwhile, the average mean plane angles for the analogous all thiophene azomethine are 9.04 (4)° and 25.07 (6)°.

Interestingly, the three-dimensional network of (I) is very different than for its all thiophene analogue in which all the molecules are linear and aligned in one direction. Since no traditional hydrogen bonding occurs, the furans and thiophene adopt a mix of parallel and perpendicular π-stacking, according to Figure 3. One such π-stacking occurs between the O21 and the O21ⁱⁱ rings with a distance of 3.674 (3) Å between the planes. Other interactions involve the oxygen or sulfur acting as electron donors while the heterocycles act as electron acceptors. For example, O11î^ interacts with O11—C11—C12—C13—C14, S1 with S1ⁱ—C16ⁱ—C17ⁱ—C18ⁱ—C19ⁱ, S2 with S2ⁱⁱ—C26ⁱⁱ—C27ⁱⁱ—C28ⁱⁱ—C29ⁱⁱ and O26ⁱⁱ with O26—C211—C212—C213—C214. The centre-to-centre distances for these interactions are 3.517 (3), 3.659 (3), 3.680 (3) and 3.541 (3) Å, respectively.

Experimental

In 25 ml of anhydrous toluene was added 2-furaldehyde to which was subsequently added DABCO, TiCl₄ in toluene at 0 °C and then diethyl 2,5-diaminothiophene-3,4-dicarboxylate. The mixture was then refluxed for two hours after which the solvent was removed. Purification by flash chromatography yielded the title product as a red solid. Single crystals of (I) were obtained by slow evaporation of a acetone.