Crystal structure and C—H⋯F hydrogen bonding in the fluorinated bis-benzoxazine: 3,3′-(ethane-1,2-di­yl)bis­(6-fluoro-3,4-di­hydro-2H-1,3-benzoxazine)

Rivera, A.; Rojas, J.J.; Ríos-Motta, J.; Bolte, M.

doi:10.1107/S2056989016015243

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Volume 72| Part 10| October 2016| Pages 1509-1511

https://doi.org/10.1107/S2056989016015243

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Crystal structure and C—H⋯F hydrogen bonding in the fluorinated bis-benzoxazine: 3,3′-(ethane-1,2-diyl)bis(6-fluoro-3,4-dihydro-2H-1,3-benzoxazine)

Augusto Rivera,^a ^* Jicli José Rojas,^a Jaime Ríos-Motta ^a and Michael Bolte ^b

^aUniversidad Nacional de Colombia, Sede Bogotá, Facultad de Ciencias, Departamento de Química, Cra 30 No. 45-03, Bogotá, Código Postal 111321, Colombia, and ^bInstitut für Anorganische Chemie, J. W. Goethe-Universität Frankfurt, Max-von Laue-Strasse, 7, 60438 Frankfurt/Main, Germany
^*Correspondence e-mail: ariverau@unal.edu.co

Edited by J. Simpson, University of Otago, New Zealand (Received 14 September 2016; accepted 28 September 2016; online 30 September 2016)

The title fluorinated bisbenzoxazine, C₁₈H₁₈F₂N₂O₂, crystallizes with one half-molecule in the asymmetric unit, which is completed by inversion symmetry. The fused oxazine ring adopts an approximately half-chair conformation. The two benzoxazine rings are oriented anti to one another around the central C—C bond. The dominant intermolecular interaction in the crystal structure is a C—H⋯F hydrogen bond between the F atoms and the axial H atoms of the OCH₂N methylene group in the oxazine rings of neighbouring molecules. C—H⋯π contacts further stabilize the crystal packing.

Keywords: crystal structure; benzoxazine; non-conventional hydrogen bonds.

CCDC reference: 1507056

1. Chemical context

Even though benzoxazines have been known for more than 60 years, a cursory look at the literature cited in relation to the polybenzoxazines in recent years reveals increasing interest in polybenzoxazine chemistry (Demir et al., 2013 ). Mannich condensation of a phenol and a primary amine with formaldehyde is perhaps the best synthetic route widely employed for the preparation of a variety of benzoxazine monomers. Mono-functional benzoxazines with one oxazine ring yield linear polymers, while bi- and polyfunctional benzoxazines produce cross-linked polymers. As a result, many kinds of benzoxazine monomers, including both mono-benzoxazines and bis-benzoxazines, have been synthesized. For composite applications, bifunctional benzoxazines are important as they produce fillers with good adhesion properties that in turn give high modulus composite materials (Santhosh-Kumar & Reghunadhan-Nair, 2014 ).

Much work in our group has been directed at the synthesis of a wide variety of bis-benzoxazines from ethylendiamine, formaldehyde and phenols in the molar ratio of 1:4:2 using a conventional method and solvent-free conditions (Rivera et al., 1989 ). Recently, we have also investigated the crystal structures of several bis-benzoxazines namely 3,3′-(ethane-1,2-diyl)bis(6-substituted-3,4-dihydro-2H-1,3-benzoxazine) derivatives (Rivera et al., 2010 , 2011 , 2012a ,b ). These were prepared to determine whether replacement of the substituents at the para position of the phenol affects the molecular conformation and possible supramolecular aggregation. In this context, the title compound is a model for studying non-conventional molecular interactions where the halogen atom may act as a hydrogen-bond acceptor. Although debate has surrounded the role of fluorine as a hydrogen-bond (HB) acceptor, the presence of such weak molecular interactions in the solid state has been the subject of both theoretical and spectroscopic studies (Dalvit & Vulpetti, 2016 ). However, to the best of our knowledge, there are few examples of X-ray studies. On the other hand, polymers containing fluorinated aromatic systems often exhibit exceptional thermal stability and show good water-repellent properties (Su & Chang, 2003 ). Therefore we report herein the crystal structure of 3,3′-(ethane-1,2-diyl)bis(6-fluoro-3,4-dihydro-2H-1,3-benzoxazine) (I), which is a very good candidate as a monomer for the investigation of the polymerization of fluorine-containing bis-benzoxazine monomers.

2. Structural commentary

The molecular structure of the title compound is illustrated in Fig. 1. The asymmetric unit contains one-half of the formula unit; a centre of inversion located at the mid-point of the central C1—C1ⁱ bond generates the other half of the bis-benzoxazine compound [symmetry code: (i) 1 − x, 1 − y, 1 − z]. Bond lengths in the benzoxazine moiety in (I) are within normal ranges and are comparable to those found in related structures (Rivera et al., 2012a,b, 2011; Chen & Wu, 2007 ).

Figure 1
The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Atoms labelled with the suffix A are generated using the symmetry operator (−x + 1, −y + 1, −z + 1).

The fused six-membered heterocyclic rings exist in an approximately half-chair conformation, characterized by a puckering amplitude Q = 0.4913 (15) Å, and θ = 52.03 (17)° and φ = 98.3 (2)°, with C2 and N1 displaced from the mean plane by −0.299 (2) and 0.331 (1) Å, respectively. The C1—C1A bond is in an axial position with a C5—N1—C1—C1A torsion angle of 75.45 (18)°. The two benzoxazine rings are oriented anti to one another about the central C1—C1A bond, with an N1—C1—C1A—N1A torsion angle of 180.0 (2)°.

3. Supramolecular features

The packing of title compound is dominated by C2—H2A⋯F1 hydrogen bonds (Table 1), that connect the molecules into a sheet structure, Fig. 2. Symmetry dictates that both F atoms are involved in these hydrogen bonds. The crystal structure also features two weak C—H⋯π interactions (Table 1), as indicated in PLATON (Spek, 2009 ), with C—H⋯Cg distances of 3.527 (2) and 3.577 (2) Å and with C—H⋯Cg angles of 126 and 129°, respectively.

Table 1
Hydrogen-bond geometry (Å, °)

Cg2 is the centroid of the C3/C4/C6/C7/C8/C9 ring

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C2—H2A⋯F1ⁱ	0.99	2.44	3.300 (2)	145
C6—H6⋯Cg2ⁱⁱ	0.95	2.88	3.527 (2)	126
C9—H9⋯Cg2ⁱⁱⁱ	0.95	2.90	3.577 (2)	129
Symmetry codes: (i) $[-x+2, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (ii) $[-x+2, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (iii) $[-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ .

Figure 2
Packing diagram for title compound, viewed along the b axis. C—H⋯F and C—F⋯π contacts are drawn as dashed lines.

4. Database survey

A database search yielded four comparable structures, 3,3′-(ethane-1,2-diyl)bis(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), and 3,3′-(ethane-1,2-diyl)bis(3,4-dihydro-2H-1,3-benzoxazine) (SAGPUN; Rivera et al., 2012a).

5. Synthesis and crystallization

The title compound was synthesized according to the literature procedure (Rivera et al.,1989), and single crystals were obtained by slow evaporation from an ethyl acetate/benzene 1:3 solvent mixture at room temperature.

6. Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were located in difference electron-density maps. C-bound H atoms were fixed geometrically (C—H = 0.95 or 0.99 Å) 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	C₁₈H₁₈F₂N₂O₂
M_r	332.34
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	173
a, b, c (Å)	7.0242 (6), 6.2316 (6), 17.1574 (15)
β (°)	91.473 (7)
V (Å³)	750.77 (12)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	0.11
Crystal size (mm)	0.17 × 0.13 × 0.04

Data collection
Diffractometer	Stoe IPDS II two-circle
Absorption correction	Multi-scan (X-AREA; Stoe & Cie, 2001 )
T_min, T_max	0.362, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	7746, 1532, 1285
R_int	0.036
(sin θ/λ)_max (Å⁻¹)	0.625

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.041, 0.101, 1.08
No. of reflections	1532
No. of parameters	109
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.18, −0.16
Computer programs: X-AREA (Stoe & Cie, 2001), SHELXS97 (Sheldrick, 2008 ), SHELXL2014 (Sheldrick, 2015 ) and XP in SHELXTL-Plus (Sheldrick, 2008).

Supporting information

CCDC reference: 1507056

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989016015243/sj5506sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989016015243/sj5506Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989016015243/sj5506Isup3.cml

checkCIF report

Computing details top

Data collection: X-AREA (Stoe & Cie, 2001); cell refinement: X-AREA (Stoe & Cie, 2001); data reduction: X-AREA (Stoe & Cie, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: XP in SHELXTL-Plus (Sheldrick, 2008); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015).

3,3'-(Ethane-1,2-diyl)bis(6-fluoro-3,4-dihydro-2H-1,3-benzoxazine) top

Crystal data top

C₁₈H₁₈F₂N₂O₂	F(000) = 348
M_r = 332.34	D_x = 1.470 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.0242 (6) Å	Cell parameters from 7746 reflections
b = 6.2316 (6) Å	θ = 3.5–27.8°
c = 17.1574 (15) Å	µ = 0.11 mm⁻¹
β = 91.473 (7)°	T = 173 K
V = 750.77 (12) Å³	Plate, colourless
Z = 2	0.17 × 0.13 × 0.04 mm

Data collection top

Stoe IPDS II two-circle diffractometer	1285 reflections with I > 2σ(I)
Radiation source: Genix 3D IµS microfocus X-ray source	R_int = 0.036
ω scans	θ_max = 26.4°, θ_min = 3.5°
Absorption correction: multi-scan (X-AREA; Stoe & Cie, 2001)	h = −8→8
T_min = 0.362, T_max = 1.000	k = −7→7
7746 measured reflections	l = −20→21
1532 independent reflections

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.041	H-atom parameters constrained
wR(F²) = 0.101	w = 1/[σ²(F_o²) + (0.0538P)² + 0.1464P] where P = (F_o² + 2F_c²)/3
S = 1.08	(Δ/σ)_max < 0.001
1532 reflections	Δρ_max = 0.18 e Å⁻³
109 parameters	Δρ_min = −0.16 e Å⁻³

Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
F1	0.80087 (14)	0.60837 (18)	0.86796 (5)	0.0408 (3)
O1	0.69940 (16)	0.06550 (17)	0.61834 (6)	0.0293 (3)
N1	0.73058 (17)	0.3605 (2)	0.52754 (7)	0.0256 (3)
C1	0.5232 (2)	0.3961 (2)	0.52148 (8)	0.0260 (3)
H1A	0.4706	0.4020	0.5744	0.031*
H1B	0.4624	0.2743	0.4934	0.031*
C2	0.7756 (2)	0.1410 (3)	0.54504 (9)	0.0294 (4)
H2A	0.9158	0.1242	0.5471	0.035*
H2B	0.7249	0.0493	0.5022	0.035*
C3	0.72790 (19)	0.2069 (2)	0.67944 (8)	0.0237 (3)
C4	0.79289 (19)	0.4168 (2)	0.66810 (8)	0.0228 (3)
C5	0.8283 (2)	0.4965 (3)	0.58624 (8)	0.0267 (3)
H5A	0.7820	0.6459	0.5809	0.032*
H5B	0.9668	0.4961	0.5770	0.032*
C6	0.81932 (19)	0.5507 (3)	0.73252 (8)	0.0250 (3)
H6	0.8647	0.6931	0.7263	0.030*
C7	0.7786 (2)	0.4732 (3)	0.80519 (8)	0.0273 (3)
C8	0.7114 (2)	0.2675 (3)	0.81752 (9)	0.0293 (4)
H8	0.6837	0.2193	0.8685	0.035*
C9	0.6854 (2)	0.1337 (3)	0.75374 (9)	0.0269 (3)
H9	0.6386	−0.0079	0.7606	0.032*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
F1	0.0442 (6)	0.0526 (7)	0.0255 (5)	−0.0053 (5)	0.0007 (4)	−0.0122 (4)
O1	0.0393 (6)	0.0227 (6)	0.0258 (6)	−0.0001 (4)	0.0008 (4)	−0.0013 (4)
N1	0.0251 (6)	0.0299 (7)	0.0217 (6)	0.0008 (5)	0.0008 (4)	0.0007 (5)
C1	0.0248 (7)	0.0289 (8)	0.0243 (7)	−0.0015 (6)	0.0006 (5)	0.0018 (6)
C2	0.0338 (8)	0.0310 (8)	0.0233 (7)	0.0046 (6)	0.0025 (6)	−0.0032 (6)
C3	0.0227 (7)	0.0253 (8)	0.0231 (7)	0.0034 (6)	−0.0003 (5)	0.0000 (6)
C4	0.0202 (6)	0.0264 (8)	0.0220 (7)	0.0014 (5)	0.0008 (5)	0.0018 (6)
C5	0.0273 (7)	0.0296 (8)	0.0232 (7)	−0.0033 (6)	0.0000 (5)	0.0032 (6)
C6	0.0210 (6)	0.0269 (8)	0.0271 (7)	−0.0004 (5)	0.0000 (5)	0.0003 (6)
C7	0.0245 (7)	0.0351 (9)	0.0223 (7)	0.0020 (6)	−0.0019 (5)	−0.0057 (6)
C8	0.0262 (7)	0.0399 (9)	0.0218 (7)	0.0026 (6)	0.0036 (6)	0.0059 (7)
C9	0.0252 (7)	0.0269 (8)	0.0287 (8)	0.0014 (6)	0.0024 (6)	0.0060 (6)

Geometric parameters (Å, º) top

F1—C7	1.3731 (17)	C3—C4	1.401 (2)
O1—C3	1.3803 (18)	C4—C6	1.393 (2)
O1—C2	1.4574 (18)	C4—C5	1.5161 (19)
N1—C2	1.434 (2)	C5—H5A	0.9900
N1—C5	1.4721 (19)	C5—H5B	0.9900
N1—C1	1.4746 (18)	C6—C7	1.374 (2)
C1—C1ⁱ	1.522 (3)	C6—H6	0.9500
C1—H1A	0.9900	C7—C8	1.384 (2)
C1—H1B	0.9900	C8—C9	1.384 (2)
C2—H2A	0.9900	C8—H8	0.9500
C2—H2B	0.9900	C9—H9	0.9500
C3—C9	1.393 (2)

C3—O1—C2	113.57 (12)	C6—C4—C5	121.16 (14)
C2—N1—C5	108.03 (12)	C3—C4—C5	119.75 (13)
C2—N1—C1	111.72 (12)	N1—C5—C4	111.15 (12)
C5—N1—C1	113.84 (12)	N1—C5—H5A	109.4
N1—C1—C1ⁱ	111.15 (14)	C4—C5—H5A	109.4
N1—C1—H1A	109.4	N1—C5—H5B	109.4
C1ⁱ—C1—H1A	109.4	C4—C5—H5B	109.4
N1—C1—H1B	109.4	H5A—C5—H5B	108.0
C1ⁱ—C1—H1B	109.4	C7—C6—C4	118.88 (15)
H1A—C1—H1B	108.0	C7—C6—H6	120.6
N1—C2—O1	113.88 (12)	C4—C6—H6	120.6
N1—C2—H2A	108.8	F1—C7—C6	118.28 (15)
O1—C2—H2A	108.8	F1—C7—C8	118.74 (13)
N1—C2—H2B	108.8	C6—C7—C8	122.95 (14)
O1—C2—H2B	108.8	C7—C8—C9	118.40 (13)
H2A—C2—H2B	107.7	C7—C8—H8	120.8
O1—C3—C9	117.09 (14)	C9—C8—H8	120.8
O1—C3—C4	122.16 (13)	C8—C9—C3	119.93 (15)
C9—C3—C4	120.75 (14)	C8—C9—H9	120.0
C6—C4—C3	119.07 (13)	C3—C9—H9	120.0

C2—N1—C1—C1ⁱ	−161.85 (15)	C1—N1—C5—C4	75.31 (15)
C5—N1—C1—C1ⁱ	75.45 (18)	C6—C4—C5—N1	−160.16 (12)
C5—N1—C2—O1	65.92 (15)	C3—C4—C5—N1	18.20 (18)
C1—N1—C2—O1	−60.03 (16)	C3—C4—C6—C7	−0.8 (2)
C3—O1—C2—N1	−45.71 (17)	C5—C4—C6—C7	177.62 (13)
C2—O1—C3—C9	−170.60 (12)	C4—C6—C7—F1	−178.47 (12)
C2—O1—C3—C4	10.67 (19)	C4—C6—C7—C8	−0.3 (2)
O1—C3—C4—C6	−179.71 (12)	F1—C7—C8—C9	178.65 (13)
C9—C3—C4—C6	1.6 (2)	C6—C7—C8—C9	0.5 (2)
O1—C3—C4—C5	1.9 (2)	C7—C8—C9—C3	0.4 (2)
C9—C3—C4—C5	−176.79 (13)	O1—C3—C9—C8	179.82 (13)
C2—N1—C5—C4	−49.39 (15)	C4—C3—C9—C8	−1.4 (2)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º) top

Cg2 is the centroid of the C3/C4/C6/C7/C8/C9 ring

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2A···F1ⁱⁱ	0.99	2.44	3.300 (2)	145
C6—H6···Cg2ⁱⁱⁱ	0.95	2.88	3.527 (2)	126
C9—H9···Cg2^iv	0.95	2.90	3.577 (2)	129

Symmetry codes: (ii) −x+2, y−1/2, −z+3/2; (iii) −x+2, y+1/2, −z+3/2; (iv) −x+1, y−1/2, −z+3/2.

Acknowledgements

We acknowledge the Dirección de Investigaciones, Sede Bogotá (DIB) de la Universidad Nacional de Colombia for financial support of this work (research project No. 28427). JJR is also grateful to COLCIENCIAS for his doctoral scholarship.

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