Crystal structure of 1-iodo-3-{[4-(tert-butylsulfanyl)phenyl]ethynyl}azulene

The title compound, C20H19IS, features a 1,3-disubstituted azulene involving an ethynylene elongated 4-(tert-butylsulfanyl)phenyl sidearm and an iodine atom as the substituents. The azulene ring system is almost planar (r.m.s. deviation = 0.012 Å) and subtends a dihedral angle of 35.7 (1)° with the benzene ring. As a result of the inherent dipole character of the azulene core, a supramolecular π–π dimer [separation between the centroids of the five- and seven-membered rings = 3.7632 (10) Å] with antiparallel orientated molecules can be observed in the crystal. The packing is consolidated by an unusual I⋯π(acetylene) contact [I⋯Cg = 3.34 Å, C—I⋯Cg = 173.3°], and a very weak C—H⋯π interaction is also found in the structure, with the azulene five-membered ring as the acceptor.


S1. Comment
Owing to the remarkable electronic and optical properties of azulene and its derivatives, compounds of this type have recently received enormous interest for application in the field of molecular electronics (Strachota et al., 2008;Xia et al., 2014) Being connected to this, the title compound, C 20 H 19 IS, is a valuable intermediate in the preparation of corresponding azulenes having a characteristic 1,3-substitution pattern (Förster et al., 2012).
The crystal structure of the compound contains one molecule in the asymmetric part of the unit cell. The molecule deviates from planarity, which can be reflected by a twist angle of 35.7° with respect to the aromatic ring systems of benzene and azulene. The ability of azulene to shift electronic density from the seven-membered ring element toward the five-membered part of the ring system has already been shown to exercise a controlling effect on the supramolecular interactions in the crystal especially regarding π-stacking behavior (Förster et al., 2014). In the present case, supramolecular dimers with a head-to-tail fashioned orientation of the azulene cores are found (3.44 Å). On the side facing away from the azulene-contact, a benzene ring is located. However, considering the distance and geometry, the existence of a π···π-interaction can be excluded. Instead, the presence of a weak C-H···π-interaction [H17···Cg(C1, C10) 2.87 Å] is assumed (Nishio et al. 2009). In the crystal of the title compound, the packing is furthermore consolidated by a remarkable I···π-interaction (Forni et al. 2012) [I1···Cg(C11, C12) 3.34 Å, 173.3°].

S2.2. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. The hydrogen atoms attached to C were fixed geometrically and treated as riding atoms, with d(C-H) = 0.93 and Uiso(H) = 1.2Ueq(C) for aromatic and Uiso(H) = 1.5Ueq(C) for methyl groups.

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level.

Figure 2
A view along the c axis of the crystal packing of the title compound.