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

The title compound 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.

Abstract

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.

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.

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 sp ² 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.

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.

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)  − x, − + y, z; (b)  − x,  + y, z.

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 4.

View of inter­molecular C—H⋯F inter­actions in the title structure (for details see Table 1 ▸).

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.

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.

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, P b c n
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 ▸)
Tmin, Tmax	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(F 2)], wR(F 2), S	0.032, 0.085, 1.03
No. of reflections	1202
No. of parameters	91
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.21, −0.24

Computer programs: CrysAlis PRO (Rigaku OD, 2020 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL (Sheldrick, 2015b ▸), and OLEX2 (Dolomanov et al., 2009 ▸).

Supplementary Material

CCDC reference: 2085161

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

supplementary crystallographic information

Crystal data

C14H6F4O2	Dx = 1.667 Mg m−3
Mr = 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

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	Rint = 0.034
Detector resolution: 10.0000 pixels mm-1	θmax = 27.1°, θmin = 1.9°
ω scans	h = −8→9
Absorption correction: gaussian (CrysAlisPro; Rigaku OD, 2020)	k = −9→9
Tmin = 0.679, Tmax = 1.000	l = −27→26
13347 measured reflections

Refinement

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(Fo2) + (0.0435P)2 + 0.4818P] where P = (Fo2 + 2Fc2)/3
S = 1.03	(Δ/σ)max < 0.001
1202 reflections	Δρmax = 0.21 e Å−3
91 parameters	Δρmin = −0.24 e Å−3
0 restraints

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
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 (Ų)

	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)

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)

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···O1iv	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.

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 Statement

This work was funded by Air Force Office of Scientific Research; National Research Council.