C—I⋯N short contacts as tools for the construction of the crystal packing in the crystal structure of 3,3′-(ethane-1,2-diyl)bis(6-iodo-3,4-dihydro-2H-1,3-benzoxazine)

The packing of the title compound features short C—I⋯N contacts.


Chemical context
Benzoxazines have been studied for more than 70 years (Holly & Cope, 1944): they are heterocyclic compounds, which have the core structure of a benzene ring fused with an oxazine ring that can be readily synthesized by the Mannich reaction of mixing three components, either in solution or by a melt-state reaction using a combination of a phenolic derivative, formaldehyde, and a primary amine (Wattanathana et al., 2014). The importance of these compounds is for the production of the corresponding polymers called polybenzoxazines, which have been developed as a class of ringopening phenolic resins (Ishida & Sanders, 2000). However, the usefulness of benzoxazines as precursors for a class of thermosetting phenolic resins with excellent mechanical and thermal properties was not recognized until recently (Velez-Herrera & Ishida, 2009).
As the electrophilic character of the substituents affects the stability both of the reaction intermediates and the benzoxazine ring (Hamerton et al., 2006), consequently, when piodophenol, formaldehyde and ethylenediamine were allowed to react in a molar ratio of 2:4:1, the title compound (I) was formed. This article forms part of our ongoing research into improving the understanding of the structural features resulting from replacement of the halogen substituent at the ISSN 2056-9890 para position of the aromatic ring of bis-1,3-benzoxazines. So, an iodine functional bis-1,3-benzoxazine, namely 3,3 0 -(ethane-1,2-diyl)bis(6-iodo-3,4-dihydro-2H-1,3-benzoxazine) has been synthesized in high yield and purity.

Structural commentary
Similar to that observed in the crystal structure of the related compounds (Rivera et al., 2010(Rivera et al., , 2016a, the asymmetric unit of the title compound C 18 H 18 I 2 N 2 O 2 , contains one-half of the formula unit; a centre of inversion is located at the mid-point of the central C1-C1(1 À x, 1 À y, 1 À z) bond (see Fig. 1). The six-membered oxazine heterocyclic ring adopts a halfchair conformation, with puckering parameters Q = 0.482 (3) Å , =129.6 (2) , ' = 283.6 (3) : with respect to the plane formed by O1/C3/C4/C5, the deviations of C2 and N1 are 0.301 (3) and À0.320 (3) Å , respectively. The observed C-O bond length [1.376 (3) Å ] is in a good agreement with the related p-fluoro and p-bromo structures (Rivera et al., 2016a,b), but this value is shorter than for the the p-chloro derivative (Rivera et al., 2010). The C7-I1 bond length

Supramolecular features
The crystal-packing arrangement of the title compound is illustrated in Fig. 2. In contrast with related structures (Rivera et al., 2016a(Rivera et al., ,b, 2010, the absence of C-HÁ Á ÁX or C-HÁ Á ÁO interactions in the title compound is surprising. The packing of title compound is dominated by short contacts (Table 1), as indicated by a PLATON (Spek, 2009) analysis. Short C-IÁ Á ÁN interactions (Table 1) are observed between neighboring molecules; it is remarkable that these short contacts present in the crystal structure of (I) has structure-directing characteristics.

Synthesis and crystallization
The title compound was prepared as described by Rivera et al. (1989). The reaction mixture was stored at room temperature for several weeks until a yellowish precipitate was formed. The Crystal packing of (I), displaying C-IÁ Á ÁN short contacts, which result in chains, forming layers propagating parallel to the bc plane. Table 1 Short-contact geometry (Å , ). (3) 3.378 (2) 169.13 (9) Symmetry code: (i) x, Ày, 1 2 + z.

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. Atoms labelled with the suffix A are generated using the symmetry operator (1 À x, 1 À y, 1 À z).
solid was separated by filtration, washed with ethanol and crystallized from acetone solution. Yield 45.5%, m.p. 434 K.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were located in the difference electron-density map. C-bound H atoms were fixed geometrically (C-H = 0.95 or 0.99Å ) and refined using a riding-model approximation, with U iso (H) set to 1.2U eq of the parent atom.   SHELXL2016 (Sheldrick, 2015); molecular graphics: XP in SHELXTL-Plus (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).