C-I⋯N short contacts as tools for the construction of the crystal packing in the crystal structure of 3,3'-(ethane-1,2-di-yl)bis-(6-iodo-3,4-di-hydro-2H-1,3-benzoxazine).

The asymmetric unit of the title compound, C18H18I2N2O2, consists of one half-mol-ecule, completed by the application of inversion symmetry. The mol-ecule adopts the typical structure for this class of bis-benxozazines, characterized by an anti orientation of the two benzoxazine rings around the central C-C bond. The oxazinic ring adopts a half-chair conformation. In the crystal, mol-ecules are linked by C-I⋯N short contacts [I⋯N = 3.378 (2) Å], generating layers lying parallel to the bc plane.

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 ring-opening 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 p-iodo­phenol, 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 para position of the aromatic ring of bis-1,3-benzoxazines. So, an iodine functional bis-1,3-benzoxazine, namely 3,3′-(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 ▸, 2016a ▸), the asymmetric unit of the title compound C18H18I2N2O2, contains one-half of the formula unit; a centre of inversion is located at the mid-point of the central C1—C1(1 − x, 1 − y, 1 − z) bond (see Fig. 1 ▸). The six-membered oxazine heterocyclic ring adopts a half-chair conformation, with puckering parameters Q = 0.482 (3) Å, θ =129.6 (2)°, φ = 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 −0.320 (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 [2.107 (3) Å] is in good agreement with the value reported for 4-iodo­phenol [2.104 (5) Å; Merz, 2006 ▸]. The C8—C9 bond length [1.378 (4) Å] is shorter than the average C–C bond length of benzene ring [1.398 (4) Å)]. The N1—C2 bond length [1.435 (3) Å] is significantly shorter than those of N1—C5 [1.474 (3) Å] and N1—C1 [1.478 (3) Å], probably due to the presence of a hyperconjugative inter­action between the lone-pair electrons of the nitro­gen atom and the anti­bonding σ orbital of C—O bond (nN→σ*C2–O1). Moreover, the C2—N1—C1 [112.6 (2)°] and C5—N1—C1 [113.0 (2)°] angles are larger than the mean value of sp 3 hybridization in ammonia (107°; Olovsson & Templeton, 1959 ▸).

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 − x, 1 − y, 1 − z).

Supra­molecular features

The crystal-packing arrangement of the title compound is illustrated in Fig. 2 ▸. In contrast with related structures (Rivera et al., 2016a ▸,b ▸, 2010 ▸), the absence of C—H⋯X or C—H⋯O 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—I⋯N 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.

Figure 2

Crystal packing of (I), displaying C—I⋯N short contacts, which result in chains, forming layers propagating parallel to the bc plane.

Table 1

Short-contact geometry (Å, °)

C—I	X	C—I	I···X	C—I···X
C7—I1	N1i	2.107 (3)	3.378 (2)	169.13 (9)

Symmetry code: (i) x, −y,  + z.

Database survey

A search of the Cambridge Structural Database (Groom et al., 2016 ▸) for short N⋯I contacts between an N atom bonded to three C atoms and an I atom bonded to an aromatic ring yielded 47 entries with a distance of less than 3.5 Å. The search yielded four comparable structures, namely 3,3′-ethane-1,2-diylbis(6-methyl-3,4-di­hydro-2H-1,3-benzoxazine) (AXAKAM; Rivera et al., 2011 ▸), 3,3′-ethyl­enebis(3,4-di­hydro-6-chloro-2H-1,3-benzoxazine), (NUQKAM; Rivera et al., 2010 ▸), 3,3′-(ethane-1,2-di­yl)-bis­(6-meth­oxy-3,4-di­hydro-2H-1,3-benzoxazine) monohydrate (QEDDOU; Rivera et al., 2012b ▸), 3,3′-ethane-1,2-diylbis(3,4-di­hydro-2H-1,3-benzoxazine) (SAGPUN; Rivera et al., 2012a ▸).

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 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.

Table 2

Experimental details

Crystal data
Chemical formula	C18H18I2N2O2
M r	548.14
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	173
a, b, c (Å)	20.4200 (9), 5.9477 (2), 17.8414 (8)
β (°)	123.607 (3)
V (Å3)	1804.69 (14)
Z	4
Radiation type	Mo Kα
μ (mm−1)	3.50
Crystal size (mm)	0.29 × 0.27 × 0.27
Data collection
Diffractometer	Stoe IPDS II two-circle
Absorption correction	Multi-scan (X-AREA; Stoe & Cie, 2001 ▸)
T min, T max	0.395, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	39259, 2531, 2456
R int	0.076
(sin θ/λ)max (Å−1)	0.697
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.030, 0.076, 1.22
No. of reflections	2531
No. of parameters	110
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	1.46, −1.35

Computer programs: X-AREA (Stoe & Cie, 2001 ▸), SHELXS97, SHELXL97 and XP in SHELXTL-Plus (Sheldrick, 2008 ▸), SHELXL2016 (Sheldrick, 2015 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989017005047/hb7668sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989017005047/hb7668Isup2.hkl

Click here for additional data file.

Supporting information file. DOI: 10.1107/S2056989017005047/hb7668Isup3.cml

CCDC reference: 1541561

Additional supporting information: crystallographic information; 3D view; checkCIF report

C18H18I2N2O2	F(000) = 1048
Mr = 548.14	Dx = 2.017 Mg m−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 20.4200 (9) Å	Cell parameters from 39259 reflections
b = 5.9477 (2) Å	θ = 3.3–29.9°
c = 17.8414 (8) Å	µ = 3.50 mm−1
β = 123.607 (3)°	T = 173 K
V = 1804.69 (14) Å3	Block, colourless
Z = 4	0.29 × 0.27 × 0.27 mm

Stoe IPDS II two-circle diffractometer	2456 reflections with I > 2σ(I)
Radiation source: Genix 3D IµS microfocus X-ray source	Rint = 0.076
ω scans	θmax = 29.7°, θmin = 3.6°
Absorption correction: multi-scan (X-AREA; Stoe & Cie, 2001)	h = −28→28
Tmin = 0.395, Tmax = 1.000	k = −7→8
39259 measured reflections	l = −24→24
2531 independent reflections

Refinement on F2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F2 > 2σ(F2)] = 0.030	w = 1/[σ2(Fo2) + (0.0378P)2 + 4.0804P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.076	(Δ/σ)max = 0.002
S = 1.22	Δρmax = 1.46 e Å−3
2531 reflections	Δρmin = −1.35 e Å−3
110 parameters	Extinction correction: SHELXL2016 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraints	Extinction coefficient: 0.0034 (2)

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

	x	y	z	Uiso*/Ueq
I1	0.60686 (2)	−0.05887 (3)	0.93105 (2)	0.02375 (9)
O1	0.68205 (12)	0.6146 (3)	0.71878 (13)	0.0231 (4)
N1	0.60465 (12)	0.4020 (4)	0.58050 (14)	0.0174 (4)
C1	0.53347 (15)	0.5410 (4)	0.54603 (16)	0.0207 (5)
H1A	0.545662	0.699539	0.541455	0.025*
H1B	0.516975	0.534394	0.588747	0.025*
C2	0.67584 (15)	0.5254 (5)	0.63881 (17)	0.0214 (5)
H2A	0.678708	0.651795	0.604633	0.026*
H2B	0.721287	0.425521	0.657944	0.026*
C3	0.66459 (15)	0.4585 (4)	0.76215 (17)	0.0187 (4)
C4	0.62686 (14)	0.2547 (4)	0.72243 (15)	0.0171 (4)
C5	0.60538 (15)	0.1994 (4)	0.62851 (16)	0.0199 (4)
H5A	0.643793	0.090235	0.632478	0.024*
H5B	0.552776	0.128136	0.594033	0.024*
C6	0.61047 (15)	0.1080 (4)	0.77133 (16)	0.0191 (4)
H6	0.585192	−0.031336	0.745502	0.023*
C7	0.63083 (15)	0.1641 (5)	0.85739 (16)	0.0208 (5)
C8	0.66757 (17)	0.3687 (5)	0.89574 (17)	0.0250 (5)
H8	0.681043	0.407706	0.954297	0.030*
C9	0.68424 (17)	0.5143 (5)	0.84831 (17)	0.0236 (5)
H9	0.709313	0.653654	0.874439	0.028*

	U11	U22	U33	U12	U13	U23
I1	0.02726 (12)	0.02815 (12)	0.01965 (12)	0.00072 (6)	0.01537 (9)	0.00344 (6)
O1	0.0281 (9)	0.0214 (8)	0.0185 (8)	−0.0058 (7)	0.0121 (7)	−0.0023 (7)
N1	0.0167 (9)	0.0205 (9)	0.0129 (8)	0.0030 (7)	0.0069 (7)	0.0024 (7)
C1	0.0207 (11)	0.0228 (11)	0.0130 (10)	0.0046 (9)	0.0060 (9)	0.0010 (8)
C2	0.0188 (10)	0.0271 (12)	0.0168 (10)	−0.0008 (9)	0.0089 (9)	0.0013 (9)
C3	0.0185 (10)	0.0207 (11)	0.0150 (10)	0.0001 (8)	0.0081 (9)	0.0021 (8)
C4	0.0166 (9)	0.0219 (10)	0.0109 (9)	0.0022 (8)	0.0064 (8)	0.0017 (8)
C5	0.0248 (11)	0.0198 (10)	0.0133 (9)	0.0014 (9)	0.0093 (9)	−0.0005 (8)
C6	0.0196 (10)	0.0197 (10)	0.0154 (10)	0.0005 (8)	0.0081 (8)	0.0009 (8)
C7	0.0235 (11)	0.0227 (11)	0.0163 (10)	0.0011 (9)	0.0110 (9)	0.0030 (9)
C8	0.0338 (13)	0.0266 (13)	0.0156 (10)	−0.0017 (11)	0.0144 (10)	−0.0019 (9)
C9	0.0311 (13)	0.0224 (11)	0.0151 (10)	−0.0037 (10)	0.0114 (10)	−0.0032 (9)

I1—C7	2.107 (3)	C3—C4	1.400 (3)
O1—C3	1.376 (3)	C4—C6	1.399 (3)
O1—C2	1.460 (3)	C4—C5	1.515 (3)
N1—C2	1.435 (3)	C5—H5A	0.9900
N1—C5	1.474 (3)	C5—H5B	0.9900
N1—C1	1.478 (3)	C6—C7	1.391 (3)
C1—C1i	1.523 (5)	C6—H6	0.9500
C1—H1A	0.9900	C7—C8	1.394 (4)
C1—H1B	0.9900	C8—C9	1.378 (4)
C2—H2A	0.9900	C8—H8	0.9500
C2—H2B	0.9900	C9—H9	0.9500
C3—C9	1.397 (4)
I1···N1ii	3.378 (2)
C3—O1—C2	113.3 (2)	C6—C4—C5	122.1 (2)
C2—N1—C5	108.45 (19)	C3—C4—C5	119.3 (2)
C2—N1—C1	112.6 (2)	N1—C5—C4	111.6 (2)
C5—N1—C1	113.0 (2)	N1—C5—H5A	109.3
N1—C1—C1i	111.0 (3)	C4—C5—H5A	109.3
N1—C1—H1A	109.4	N1—C5—H5B	109.3
C1i—C1—H1A	109.4	C4—C5—H5B	109.3
N1—C1—H1B	109.4	H5A—C5—H5B	108.0
C1i—C1—H1B	109.4	C7—C6—C4	120.7 (2)
H1A—C1—H1B	108.0	C7—C6—H6	119.7
N1—C2—O1	113.5 (2)	C4—C6—H6	119.7
N1—C2—H2A	108.9	C6—C7—C8	120.1 (2)
O1—C2—H2A	108.9	C6—C7—I1	120.46 (19)
N1—C2—H2B	108.9	C8—C7—I1	119.41 (18)
O1—C2—H2B	108.9	C9—C8—C7	119.7 (2)
H2A—C2—H2B	107.7	C9—C8—H8	120.2
O1—C3—C9	116.9 (2)	C7—C8—H8	120.2
O1—C3—C4	122.7 (2)	C8—C9—C3	120.5 (3)
C9—C3—C4	120.3 (2)	C8—C9—H9	119.7
C6—C4—C3	118.6 (2)	C3—C9—H9	119.7
C2—N1—C1—C1i	150.8 (3)	C1—N1—C5—C4	−77.2 (2)
C5—N1—C1—C1i	−85.9 (3)	C6—C4—C5—N1	161.7 (2)
C5—N1—C2—O1	−65.2 (3)	C3—C4—C5—N1	−18.6 (3)
C1—N1—C2—O1	60.5 (3)	C3—C4—C6—C7	0.4 (4)
C3—O1—C2—N1	47.5 (3)	C5—C4—C6—C7	−179.9 (2)
C2—O1—C3—C9	167.3 (2)	C4—C6—C7—C8	0.3 (4)
C2—O1—C3—C4	−14.5 (3)	C4—C6—C7—I1	−179.47 (18)
O1—C3—C4—C6	−179.0 (2)	C6—C7—C8—C9	−0.6 (4)
C9—C3—C4—C6	−0.9 (4)	I1—C7—C8—C9	179.2 (2)
O1—C3—C4—C5	1.2 (4)	C7—C8—C9—C3	0.1 (4)
C9—C3—C4—C5	179.3 (2)	O1—C3—C9—C8	178.9 (3)
C2—N1—C5—C4	48.3 (3)	C4—C3—C9—C8	0.7 (4)