Crystal structure of 1,2-bis­(3,5-di­fluoro­phen­yl)ethane-1,2-dione

Brown, L.C.; Balaich, G.J.

doi:10.1107/S2056989021005363

research communications

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ISSN: 2056-9890

Volume 77| Part 7| July 2021| Pages 700-702

https://doi.org/10.1107/S2056989021005363

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Crystal structure of 1,2-bis(3,5-difluorophenyl)ethane-1,2-dione

Loren C. Brown ^a ^* and Gary J. Balaich ^a

^aDepartment of Chemistry & Chemistry Research Center, United States Air Force Academy, Colorado Springs, CO 80840, USA
^*Correspondence e-mail: Gary.Balaich@usafa.edu

Edited by A. V. Yatsenko, Moscow State University, Russia (Received 17 February 2021; accepted 21 May 2021; online 8 June 2021)

The title compound, C₁₄H₆F₄O₂, crystallizes with half of a molecule per asymmetric unit and exhibits bond lengths and angles typical of α-diketones. A network of C—H⋯F contacts and π–π stacking interactions is observed within the structure.

Keywords: crystal structure; diketone; C—H⋯F interactions.

CCDC reference: 2085161

1. Chemical context

Aryl diketones are a class of dicarbonyl compounds with a wide variety of uses in organic synthesis. The title α-diketone, 1,2-bis(3,5-difluorophenyl)ethane-1,2-dione, is used as a precursor in the production of hexabenzocoronenes (Jones et al., 2012 ). More recently, 1,2-bis(3,5-difluorophenyl)ethane-1,2-dione has been used in the synthesis of various polymers that have been studied for photovoltaics (Cai et al., 2019 ) and for gas chromatography (GC) stationary phases (Liu et al., 2019 ). Although the synthetic chemistry is known in the literature, to the best of our knowledge, structural data have not yet been published for the title compound. Herein we report the crystal structure of 1,2-bis(3,5-difluorophenyl)ethane-1,2-dione, isolated as a minor impurity in the synthesis of the related 1,4-diarylketone, 1-(3,5-difluorophenyl)pentane-1,4-dione.

2. Structural commentary

The title compound (Fig. 1) crystallized in the orthorhombic space group Pbcn. Benzil (1,2-diphenylethane-1,2-dione) and similar α,α-diketones crystallize in trigonal or monoclinic space groups, respectively (Charpe et al., 2020 ; El Moncef et al., 2010 ; Fun et al., 2008 ). The title compound crystallizes with one half-molecule per asymmetric unit (Z′ = 0.5), and exhibits the expected bond lengths and angles for α-diketone sp² hybridized atoms. Interestingly, the C5—C6—C7—O1 torsion angle [7.55 (19)°] of the title compound is larger compared to the same torsion angle in bis(4-fluorophenyl)ethane-1,2-dione [5.69 (18)°; Fun et al., 2008] and benzil [3.80 (18)°; Charpe et al., 2020], but smaller compared to 1,2-bis(3-methoxyphenyl)ethane-1,2-dione [7.94 (15)°; Goossens et al., 2005 ]. The dihedral angle between the two rings is 49.50 (6)° with a C6—C7—C7′—C6′torsion angle of 125.92 (5)°.

Figure 1
The molecular structure of 1,2-bis(3,5-difluorophenyl)ethane-1,2-dione. Displacement ellipsoids are shown at the 50% probability level.

3. Supramolecular features

A view of crystal packing of the title compound is presented in Fig. 2. The molecules pack in a stacking pattern maximizing slipped π-π stacking interactions between planes of the difluoroaryl rings with an intercentroid separation of 3.7317 (8) Å, thus forming layers parallel to the bc plane (Fig. 3). Similar π–π stacking interactions with comparable intercentroid separations were observed in bis(4-fluorophenyl)ethane-1,2-dione [3.6416 (9) Å; Fun et al., 2008] and benzil [3.7566 (17) Å; Charpe et al., 2020]. As a result of the packing arrangement of bis(3-methoxyphenyl)ethane-1,2-dione, no π–π stacking interactions were observed (Goossens et al., 2005). The title compound packs in a way that allows close contacts between the fluorine atoms and hydrogen atoms of adjacent molecules, leading to a network of C—H⋯F interactions (Table 1, Fig. 4) as well as fluorine interactions between neighboring molecules [F1⋯F2(1 + x, y, z) = 2.9372 (16) Å, F1⋯F1(2 − x, 1 − y, 1 − z) = 2.8614 (16) Å]. A network of C—H⋯O interactions is also observed between the carbonyl oxygen and H5. This interaction is significantly weaker for 1,2-bis(3,5-difluorophenyl)ethane-1,2-dione in comparison to benzil (O⋯H = 2.42 Å) and bis(4-fluorophenyl)ethane-1,2-dione (O⋯H = 2.40 Å). As a result, the π–π stacking and C—H⋯ F interactions play a vital role in how the compound packs within the crystal structure.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C1—H1⋯F2ⁱ	0.93	2.48	3.2281 (16)	137
C3—H3⋯F1ⁱⁱ	0.93	2.46	3.3211 (15)	154
C5—H5⋯O1ⁱⁱⁱ	0.93	2.65	3.517 (2)	156
Symmetry codes: (i) x+1, y, z; (ii) $[x-{\script{1\over 2}}, -y+{\script{3\over 2}}, -z+1]$ ; (iii) $[-x+1, y, -z+{\script{1\over 2}}]$ .

Figure 2
A packing view of 1,2-bis(3,5-difluorophenyl)ethane-1,2-dione.

Figure 3
View of π–π stacking interactions in the title structure. Short intercentroid separations are shown by dashed lines. Cg1 is the centroid of the C1–C6 ring.Symmetry codes: (a) $[{3\over 2}]$ − x, − $[{1\over 2}]$ + y, z; (b) $[{3\over 2}]$ − x, $[{1\over 2}]$ + y, z.

Figure 4
View of intermolecular C—H⋯F interactions in the title structure (for details see Table 1

4. Database survey

A search of the Cambridge Structural Database (CSD, version of December 2019; Groom et al., 2016 ) for aryl substituted α-diketones yielded 178 results. The bond lengths and angles in the title molecule are consistent with α,α-diketones reported in the literature. The most closely related compound was compared to the title compound in the preceeding sections.

5. Synthesis and crystallization

Colorless crystals of the title compound suitable for single-crystal X-ray diffraction study were obtained by slow evaporation of a dichloromethane solution of the residue left after isolation of 1-(3,5-difluorophenyl)pentane-1,4-dione.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were positioned geometrically (C—H = 0.93 Å) and refined as riding with U_iso(H) = 1.2U_eq(C).

Table 2
Experimental details

Crystal data
Chemical formula	C₁₄H₆F₄O₂
M_r	282.19
Crystal system, space group	Orthorhombic, Pbcn
Temperature (K)	100
a, b, c (Å)	7.0588 (2), 7.4008 (2), 21.5265 (4)
V (Å³)	1124.56 (5)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.16
Crystal size (mm)	0.30 × 0.14 × 0.10

Data collection
Diffractometer	XtaLAB Synergy, Single source at offset/far, HyPix3000
Absorption correction	Gaussian (CrysAlis PRO; Rigaku OD, 2020 $[Rigaku OD (2020). CrysAlis PRO, CrysAlis CCD and CrysAlis RED. Rigaku Oxford Diffraction, Yarnton, England.]$ )
T_min, T_max	0.679, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	13347, 1202, 1014
R_int	0.034
(sin θ/λ)_max (Å⁻¹)	0.641

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.032, 0.085, 1.03
No. of reflections	1202
No. of parameters	91
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.21, −0.24
Computer programs: CrysAlis PRO (Rigaku OD, 2020 $[Rigaku OD (2020). CrysAlis PRO, CrysAlis CCD and CrysAlis RED. Rigaku Oxford Diffraction, Yarnton, England.]$ ), SHELXT (Sheldrick, 2015a ), SHELXL (Sheldrick, 2015b ), and OLEX2 (Dolomanov et al., 2009 ).

Supporting information

CCDC reference: 2085161

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989021005363/yk2148sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989021005363/yk2148Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989021005363/yk2148Isup3.cdx

Supporting information file. DOI: https://doi.org/10.1107/S2056989021005363/yk2148Isup4.cml

checkCIF report

Computing details top

Data collection: CrysAlis PRO (Rigaku OD, 2020); cell refinement: CrysAlis PRO (Rigaku OD, 2020); data reduction: CrysAlis PRO (Rigaku OD, 2020); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

1,2-Bis(3,5-difluorophenyl)ethane-1,2-dione top

Crystal data top

C₁₄H₆F₄O₂	D_x = 1.667 Mg m⁻³
M_r = 282.19	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbcn	Cell parameters from 7273 reflections
a = 7.0588 (2) Å	θ = 1.9–27.0°
b = 7.4008 (2) Å	µ = 0.16 mm⁻¹
c = 21.5265 (4) Å	T = 100 K
V = 1124.56 (5) Å³	Block, colourless
Z = 4	0.30 × 0.14 × 0.10 mm
F(000) = 568

Data collection top

XtaLAB Synergy, Single source at offset/far, HyPix3000 diffractometer	1202 independent reflections
Radiation source: micro-focus sealed X-ray tube, PhotonJet (Mo) X-ray Source	1014 reflections with I > 2σ(I)
Mirror monochromator	R_int = 0.034
Detector resolution: 10.0000 pixels mm^-1	θ_max = 27.1°, θ_min = 1.9°
ω scans	h = −8→9
Absorption correction: gaussian (CrysAlisPro; Rigaku OD, 2020)	k = −9→9
T_min = 0.679, T_max = 1.000	l = −27→26
13347 measured reflections

Refinement top

Refinement on F²	Primary atom site location: dual
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.032	H-atom parameters constrained
wR(F²) = 0.085	w = 1/[σ²(F_o²) + (0.0435P)² + 0.4818P] where P = (F_o² + 2F_c²)/3
S = 1.03	(Δ/σ)_max < 0.001
1202 reflections	Δρ_max = 0.21 e Å⁻³
91 parameters	Δρ_min = −0.24 e Å⁻³
0 restraints

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	1.04484 (11)	0.64342 (12)	0.45793 (3)	0.0274 (2)
F2	0.41188 (11)	0.52722 (13)	0.40758 (4)	0.0298 (2)
O1	0.78193 (13)	0.28658 (13)	0.22568 (4)	0.0236 (3)
C1	0.97690 (19)	0.50922 (17)	0.36170 (6)	0.0183 (3)
H1	1.1050	0.5083	0.3516	0.022*
C2	0.91452 (19)	0.57731 (18)	0.41774 (6)	0.0196 (3)
C3	0.72718 (19)	0.58412 (18)	0.43505 (6)	0.0200 (3)
H3	0.6896	0.6293	0.4734	0.024*
C4	0.59783 (19)	0.51991 (19)	0.39216 (6)	0.0200 (3)
C5	0.64773 (18)	0.44830 (18)	0.33558 (6)	0.0190 (3)
H5	0.5563	0.4056	0.3081	0.023*
C6	0.84090 (18)	0.44170 (17)	0.32055 (6)	0.0167 (3)
C7	0.89509 (18)	0.36177 (17)	0.25965 (6)	0.0174 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
F1	0.0235 (5)	0.0368 (5)	0.0218 (4)	−0.0053 (4)	−0.0033 (3)	−0.0094 (3)
F2	0.0151 (4)	0.0487 (6)	0.0254 (5)	0.0037 (4)	0.0047 (3)	−0.0003 (4)
O1	0.0235 (5)	0.0298 (6)	0.0176 (5)	−0.0056 (4)	−0.0014 (4)	−0.0014 (4)
C1	0.0160 (6)	0.0201 (7)	0.0188 (7)	−0.0005 (5)	0.0007 (5)	0.0009 (5)
C2	0.0203 (7)	0.0210 (7)	0.0174 (6)	−0.0013 (5)	−0.0030 (5)	−0.0009 (5)
C3	0.0232 (7)	0.0200 (7)	0.0168 (6)	0.0026 (6)	0.0025 (5)	−0.0003 (5)
C4	0.0142 (7)	0.0240 (7)	0.0220 (7)	0.0024 (5)	0.0028 (5)	0.0046 (5)
C5	0.0170 (6)	0.0230 (7)	0.0168 (6)	−0.0012 (5)	−0.0023 (5)	0.0029 (5)
C6	0.0169 (7)	0.0168 (7)	0.0162 (6)	0.0000 (5)	0.0005 (5)	0.0024 (5)
C7	0.0184 (7)	0.0178 (6)	0.0161 (6)	−0.0001 (5)	−0.0011 (5)	0.0036 (5)

Geometric parameters (Å, º) top

F1—C2	1.3543 (15)	C3—H3	0.9300
F2—C4	1.3550 (15)	C3—C4	1.3827 (19)
O1—C7	1.2176 (16)	C4—C5	1.3741 (19)
C1—H1	0.9300	C5—H5	0.9300
C1—C2	1.3796 (18)	C5—C6	1.4023 (18)
C1—C6	1.3985 (18)	C6—C7	1.4882 (17)
C2—C3	1.3748 (19)	C7—C7ⁱ	1.538 (3)

C2—C1—H1	121.1	C5—C4—C3	123.72 (13)
C2—C1—C6	117.73 (12)	C4—C5—H5	121.1
C6—C1—H1	121.1	C4—C5—C6	117.85 (12)
F1—C2—C1	118.28 (11)	C6—C5—H5	121.1
F1—C2—C3	117.84 (11)	C1—C6—C5	120.59 (12)
C3—C2—C1	123.87 (13)	C1—C6—C7	121.56 (12)
C2—C3—H3	121.9	C5—C6—C7	117.84 (11)
C2—C3—C4	116.21 (12)	O1—C7—C6	122.83 (12)
C4—C3—H3	121.9	O1—C7—C7ⁱ	117.99 (12)
F2—C4—C3	117.54 (12)	C6—C7—C7ⁱ	119.05 (12)
F2—C4—C5	118.74 (12)

Symmetry code: (i) −x+2, y, −z+1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1···F2ⁱⁱ	0.93	2.48	3.2281 (16)	137
C3—H3···F1ⁱⁱⁱ	0.93	2.46	3.3211 (15)	154
C5—H5···O1^iv	0.93	2.65	3.517 (2)	156

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

Selected bond distances (Å) and angles (°) for 1,2-bis(3,5-difluorophenyl)ethane-1,2-dione. top

C1–C2	1.3796 (18)
C1–C6	1.3985 (18)
C2–C3	1.3748 (19)
C3–C4	1.3827 (19)
C4–C5	1.3741 (19)
C5–C6	1.4023 (18)
C6–C7	1.4882 (17)
C7–C7'	1.538 (3)
C7–O1	1.2176 (16)
F1–C2	1.3543 (15)
F2–C4	1.3550 (15)

C1–C6–C5	120.59 (12)
C1–C6–C7	121.56 (12)
C2–C1–C6	117.73 (12)
C2–C3–C4	116.21 (12)
C3–C2–C1	123.87 (13)
C4–C5–C6	117.85 (12)
C5–C4–C3	123.72 (13)
C5–C6–C7	117.84 (11)
C6–C7–C7'	119.05 (12)
O1–C7–C6	122.83 (12)
O1–C7–C7'	117.99 (12)
F1–C2–C1	118.28 (11)
F1–C2–C3	117.84 (11)
F2–C4–C3	117.54 (12)
F2–C4–C5	118.74 (12)

Funding information

Funding for this research was provided by: Air Force Office of Scientific Research; National Research Council (award to LCB).

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