Crystal structure of diethyl 2-amino-6-[(thiophen-3-yl)ethynyl]azulene-1,3-dicarboxylate

The title compound, C22H19NO4S, has an almost planar geometry supported by intramolecular N—H⋯O and C—H⋯O hydrogen bonds. The thiophene ring is inclined to the azulene ring by 4.85 (16)°, while the ethoxycarbonyl groups are inclined to the azulene ring by 7.0 (2) and 5.7 (2)°. In the crystal, molecules are linked by pairs of N—H⋯O hydrogen bonds, forming inversion dimers with an R 2 2(12) ring motif. The dimers are linked via C—H⋯π interactions, forming sheets parallel to (10-1).


Related literature
For the synthesis of the title compound concerning the azulene-derived starting material, see: McDonald et al. (1976).   Table 1 Hydrogen-bond geometry (Å , ).

S2. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-and N-bound H atoms were fixed geometrically and treated as riding: N-H = 0.86 Å, C-H = 0.93 -0.97 Å, with U iso (H) =1.5U eq (C) for methyl H atoms and = 1.2U eq (N,C) for other H atoms.

S3. Comment
Due to the special physical properties including redox behavior, azulene is an interesting structure building block for electronic materials design (Förster et al., 2012;Shoji et al., 2013;Xia et al., 2014). In this regard, the present tetrasubstituted azulene derivative, as the title compound, represents a promising intermediate.
The title compound has an almost planar overall geometry with maximum deviations of 0.166 (1) Å for C20 and 0.267 (4) Å for C6 ( Fig. 1). In contrast to previously published related compounds (Förster et al., 2014), here the amine group gives rise to the formation of two intramolecular N-H···O hydrogen bonds to the neighbouring carbonyl O atoms O1 and O3 (Table 1 and Fig. 1). Furthermore, atoms O2 and O4 establish two weaker intramolecular C-H···O hydrogen bonds to azulene hydrogen atoms (Table 1 and Fig. 1).
In the crystal, an R 2 2 (12) hydrogen bonded inversion dimer motif is formed (Table 1 and Fig. 2). Along the crystallographic b-axis, the corresponding dimers are arranged in stacks (Fig. 2). Despite a plane to plane distance of 3.15 supporting information Å between the azulene units of consecutive molecules, no arene···arene interactions can be observed due to the lateral displacement. In direction of the crystallographic a-and c-axes, these stacks are connected via C-H···π contacts [ Table   1; Nishio et al., 2009] and weak van der Waals forces, forming a sheets parallel to (10\1).. The absence of arene···arene interactions is a rather rare phenomenon for this class of azulenes, and is probably due to packing effects (Förster et al., 2014).

Figure 1
A view of the molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The hydrogen bonds are shown as dashed lines (see Table 1 for details).

Figure 2
Crystal packing of the title compound viewed along the b-axis. Hydrogen bonds are shown as dashed lines (see Table 1 for details). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.68 e Å −3 Δρ min = −0.69 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.