1,4-Di-n-hept­yloxy-2,5-dinitro­benzene

Blackburn, O.A.; Coe, B.J.; Futhey, R.; Helliwell, M.

doi:10.1107/S160053680905123X

organic compounds

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ISSN: 2056-9890

Volume 66| Part 1| January 2010| Page o36

doi:10.1107/S160053680905123X

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1,4-Di-n-heptyloxy-2,5-dinitrobenzene

Octavia A. Blackburn,^a Benjamin J. Coe,^a ^* Robert Futhey ^a and Madeleine Helliwell ^a

^aSchool of Chemistry, University of Manchester, Manchester M13 9PL, England
^*Correspondence e-mail: b.coe@manchester.ac.uk

(Received 20 November 2009; accepted 27 November 2009; online 4 December 2009)

The complete molecule of the title compound, C₂₀H₃₂N₂O₆, is generated by crystallographic inversion symmetry. The two mutually trans nitro substituents are hence in fully eclipsed conformation and also twisted by 43.2 (2)° with respect to the phenyl ring plane. The benzene-connected portions of the alkoxy substituents lie almost coplanar with the ring [C—O—C—C torsion angle = 2.0 (2)°]. In the crystal, weak C—H⋯O interactions link the molecules.

Related literature

For general background to the synthesis, see: Baker et al. (2008 ); Fisher et al. (1975 ); Flader et al. (2000 ); Hammershøj et al. (2006 ); Kawai et al. (1959 ). For a related structure, see: Voss et al. (2003 ).

Experimental

Crystal data

C₂₀H₃₂N₂O₆
M_r = 396.48
Monoclinic, P 2₁ /c
a = 13.988 (2) Å
b = 7.9454 (13) Å
c = 9.5344 (15) Å
β = 99.786 (3)°
V = 1044.3 (3) Å³
Z = 2
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 100 K
0.40 × 0.40 × 0.25 mm

Data collection

Bruker SMART CCD area-detector diffractometer
5776 measured reflections
2110 independent reflections
1733 reflections with I > 2σ(I)
R_int = 0.035

Refinement

R[F² > 2σ(F²)] = 0.035
wR(F²) = 0.093
S = 1.03
2110 reflections
128 parameters
H-atom parameters constrained
Δρ_max = 0.24 e Å⁻³
Δρ_min = −0.19 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C3—H3⋯O2ⁱ	0.95	2.50	3.4525 (15)	179
C4—H4B⋯O1ⁱⁱ	0.99	2.53	3.2852 (15)	133
Symmetry codes: (i) $[x, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ ; (ii) x, y+1, z.

Data collection: SMART (Bruker, 2001 ); cell refinement: SAINT (Bruker, 2002 ); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL .

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S160053680905123X/pv2242sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S160053680905123X/pv2242Isup2.hkl

checkCIF report

Comment top

The title compound, (I), is the minor product formed from the nitration of 1,4-di(n-heptoxy)benzene and was synthesized as a precursor to derivatized "salen-like" ligands for co-ordination to transition metals. Although (I) is commercially available, apparently a synthetic method has not been reported previously. Our synthesis involves a standard nitration procedure (Hammershøj et al., 2006) and produces a mixture of the 2,3 and 2,5 structural isomers in a ca 2:1 ratio as indicated by the ¹H NMR spectrum of the crude material. The isomeric ratio produced in such reactions is clearly quite variable. For example, nitration of 1,4-dimethoxybenzene by a very similar method, but with heating at 373 K for 1 h produced the 2,3 isomer in 90% yield after recrystallization (Hammershøj et al., 2006). Similar results were reported previously (Flader et al., 2000; Fisher et al., 1975), while nitration of 1,4-di(n-butoxy)benzene in a mixture of nitric and acetic acids gives the 2,3 and 2,5 isomers in a 4:1 ratio (Kawai et al., 1959; Baker et al., 2008).

Having structural confirmation for (I), the two isomers are also distinguished by significant differences in their ¹H NMR spectra, especially a high field shift of 0.36 p.p.m. for the singlet assigned to the two phenyl protons on moving from 2,5 to 2,3-isomer. This change can be attributed to an increased extent of shielding when these protons are located meta rather than ortho to the nitro substituents. The two isomers also show significantly different melting points and electronic absorption spectra. Compound (I) melts at a temperature ca 70 K higher than that observed for its 2,3-isomer, indicating that the forces holding together the crystal lattice are considerably stronger for (I). A similarly large difference in melting points has also been reported for the corresponding n-butoxy compounds (Kawai et al., 1959).

Both isomers show relatively intense near UV absorption bands that are responsible for their observed colours. These bands are attributable to π→ π* intramolecular charge-transfer (ICT) excitations from the HOMO primarily localized on the electron-rich heptoxy groups to the LUMO localized on the electron-deficient nitro units. The stronger yellow colour of (I) when compared with its 2,3-isomer is due to the ICT band maximum being lower in energy by ca 940 cm^-1, with an approximately doubled molar extinction coefficient, producing more extensive tailing of the absorption into the visible region. Clearly, both the HOMO-LUMO energy gap and the extent of overlap between these orbitals are affected significantly by isomerization.

Compound (I) readily forms large and high-quality, yellow block-shaped crystals upon slow evaporation of a n-hexane/ethyl acetate solution. Its structure (Fig. 1) resembles that reported previously for the compound 2-(n-heptoxy)-5-methoxy-3,6-dinitrobenzaldehyde (Voss et al., 2003), with generally similar geometric parameters. In both compounds, the two mutually trans nitro substituents are twisted with respect to the phenyl ring plane. However, in (I) these groups are fully eclipsed, since they are related by inversion, each with a O2—N1—C1—C2 torsion angle of 43.2 (2)°, while their mutual orientation is staggered in the previously published structure, with corresponding angles of 39.3 (5) and 87.5 (4)°. Another difference between these two structures is the relative orientations of their alkoxy substituents. In (I), for the inversion-related alkoxy groups C4—O3—C2—C3, the torsion angles are very small (2.0 (2)°), but in 2-(n-heptoxy)-5-methoxy-3,6-dinitrobenzaldehyde, the C—O—C—C angles are quite different, being 1.0 (5)° for the methoxy substituent, while the OCH₂ unit of the heptoxy group is almost perpendicular to the phenyl ring, with a C—O—C—C torsion angle of 86.9 (4)°.

Related literature top

For general background to the synthesis, see: Baker et al. (2008); Fisher et al. (1975); Flader et al. (2000); Hammershøj et al. (2006); Kawai et al. (1959). For a related structure, see: Voss et al. (2003).

Experimental top

Synthesis of 1,4-di(n-heptoxy)benzene. A solution of hydroquinone (5.00 g, 0.045 mol), 1-bromo-n-heptane (17.9 g, 0.100 mol) and K₂CO₃ (25.1 g, 0.182 mol) in DMF (100 ml) was heated at reflux for 3 h. The resulting brown solution was poured into cold water and the brown precipitate filtered off, washed with cold water and recrystallized from ethanol to give a colourless solid (yield 7.22 g, 52%).

Synthesis of 1,4-di(n-heptoxy)-2,5-dinitrobenzene (I). 1,4-di(n-heptoxy)benzene (200 mg, 0.653 mmol) was added slowly to stirred, ice cooled nitric acid (67%, 5 ml). The solution was stirred at 273 K for 1 h, at room temperature for 1 h and then at 313 K for 1 h. The reaction mixture was poured into iced water (10 g) and the product extracted into chloroform (10 ml). The yellow solution was dried over MgSO₄ and evaporated to give a mixture of the 2,3-dinitro and 2,5-dinitro isomers as a yellow solid (yield 247 mg, 95%). The isomers were separated by silica gel column chromatography. Elution with n-hexane/ethyl acetate (99:1) gave (I) as a bright yellow solid (yield 71 mg, 27%). Diffraction-quality crystals were grown by slow evaporation of a n-hexane/ethyl acetate solution. Further elution of the column with n-hexane/ethyl acetate (95:5) gave the 2,3-dinitro isomer as a pale yellow solid (yield 123 mg, 48%).

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top

	Fig. 1. View of the compound (I) (50% probability displacement ellipsoids); [symmetry code: A = -x + 1, -y, -z + 2].
	Fig. 2. Synthesis of compound (I) and its isomeric form.

1,4-Di-n-heptyloxy-2,5-dinitrobenzene top

Crystal data top

C₂₀H₃₂N₂O₆	F(000) = 428
M_r = 396.48	D_x = 1.261 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 776 reflections
a = 13.988 (2) Å	θ = 3.0–26.2°
b = 7.9454 (13) Å	µ = 0.09 mm⁻¹
c = 9.5344 (15) Å	T = 100 K
β = 99.786 (3)°	Block, yellow
V = 1044.3 (3) Å³	0.40 × 0.40 × 0.25 mm
Z = 2

Data collection top

Bruker SMART CCD area-detector diffractometer	1733 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.035
Graphite monochromator	θ_max = 26.3°, θ_min = 3.0°
phi and ω scans	h = −15→17
5776 measured reflections	k = −9→9
2110 independent reflections	l = −8→11

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.035	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.093	H-atom parameters constrained
S = 1.03	w = 1/[σ²(F_o²) + (0.0502P)² + 0.0454P] where P = (F_o² + 2F_c²)/3
2110 reflections	(Δ/σ)_max < 0.001
128 parameters	Δρ_max = 0.24 e Å⁻³
0 restraints	Δρ_min = −0.19 e Å⁻³

Crystal data top

C₂₀H₃₂N₂O₆	V = 1044.3 (3) Å³
M_r = 396.48	Z = 2
Monoclinic, P2₁/c	Mo Kα radiation
a = 13.988 (2) Å	µ = 0.09 mm⁻¹
b = 7.9454 (13) Å	T = 100 K
c = 9.5344 (15) Å	0.40 × 0.40 × 0.25 mm
β = 99.786 (3)°

Data collection top

Bruker SMART CCD area-detector diffractometer	1733 reflections with I > 2σ(I)
5776 measured reflections	R_int = 0.035
2110 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.035	0 restraints
wR(F²) = 0.093	H-atom parameters constrained
S = 1.03	Δρ_max = 0.24 e Å⁻³
2110 reflections	Δρ_min = −0.19 e Å⁻³
128 parameters

Special details top

Experimental. Characterization data for 1,4-di(n-heptoxy)benzene. Found: C 78.76, H 11.14%. Calculated for C₂₀H₃₄O₂: C 78.38, H, 11.18%. ¹H NMR (300 MHz, CDCl₃): 6.82 (4H, s, C₆H₄), 3.89 (4H, t, J = 6.6 Hz, 2OCH₂), 1.75 (4H, quintet, J = 6.7 Hz, 2CH₂), 1.50-1.18 (16H, m, 8CH₂), 0.89 (6H, t, J = 6.8 Hz, 2CH₃).

Characterization data for 1,4-di(n-heptoxy)-2,5-dinitrobenzene (I). Melting point = 387-389 K. Found: C 60.81, H 8.29, N 6.94%. Calculated for C₂₀H₃₂N₂O₆: C 60.59, H 8.14, N 7.07%. ¹H NMR (400 MHz, CDCl₃): 7.51 (2H, s, C₆H₂), 4.08 (4H, t, J = 6.5 Hz, 2OCH₂), 1.83 (4H, quintet, J = 6.6 Hz, 2CH₂), 1.50-1.25 (16H, m, 8CH₂), 0.89 (6H, t, J = 6.7 Hz, 2CH₃). +Electrospray MS: m/z = 419.2 [M + Na]⁺, 815.8 [2M + Na]⁺. (λ_max = 378 nm, ε = 5000 M^-1 dm³ in dichloromethane). ν(NO₂) = 1531 and 1352 cm^-1.

Characterization data for 1,4-di(n-heptoxy)-2,3-dinitrobenzene. Melting point = 318-319 K. Found: C 60.66, H 8.56, N 7.09%. Calculated for C₂₀H₃₂N₂O₆: C 60.59, H 8.14, N 7.07%. ¹H NMR (400 MHz, CDCl₃): 7.15 (2H, s, C₆H₂), 4.05 (4H, t, J = 6.5 Hz, 2OCH₂), 1.76 (4H, quintet, J = 6.5 Hz, 2CH₂), 1.45-1.25 (16H, m, 8CH₂), 0.89 (6H, t, J = 6.7 Hz, 2CH₃). (λ_max = 365 nm, ε = 2300 M^-1 dm³ in dichloromethane). ν(NO₂) = 1537 and 1358 cm^-1.

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	U_iso*/U_eq
O1	0.60328 (6)	−0.29610 (10)	0.79050 (10)	0.0209 (2)
O2	0.58901 (6)	−0.06141 (10)	0.67325 (9)	0.0233 (2)
O3	0.63728 (6)	0.17278 (10)	0.87825 (9)	0.0194 (2)
N1	0.58118 (7)	−0.14678 (12)	0.77792 (11)	0.0158 (2)
C1	0.54045 (8)	−0.06789 (14)	0.89396 (12)	0.0146 (3)
C2	0.56913 (8)	0.09431 (15)	0.94007 (12)	0.0153 (3)
C3	0.52640 (8)	0.16163 (14)	1.04846 (13)	0.0156 (3)
H3	0.5431	0.2718	1.0830	0.019*
C4	0.66991 (9)	0.33643 (14)	0.93230 (13)	0.0179 (3)
H4A	0.6913	0.3318	1.0367	0.022*
H4B	0.6168	0.4198	0.9110	0.022*
C5	0.75354 (8)	0.38479 (15)	0.85918 (13)	0.0187 (3)
H5A	0.7716	0.5033	0.8825	0.022*
H5B	0.7324	0.3770	0.7549	0.022*
C6	0.84229 (9)	0.27363 (16)	0.90244 (15)	0.0226 (3)
H6A	0.8267	0.1586	0.8657	0.027*
H6B	0.8565	0.2669	1.0076	0.027*
C7	0.93312 (9)	0.33431 (16)	0.84913 (14)	0.0217 (3)
H7A	0.9219	0.3296	0.7439	0.026*
H7B	0.9457	0.4531	0.8779	0.026*
C8	1.02172 (9)	0.22911 (16)	0.90717 (15)	0.0236 (3)
H8A	1.0301	0.2290	1.0124	0.028*
H8B	1.0095	0.1116	0.8746	0.028*
C9	1.11579 (9)	0.28829 (18)	0.86375 (15)	0.0263 (3)
H9A	1.1257	0.4087	0.8887	0.032*
H9B	1.1104	0.2779	0.7592	0.032*
C10	1.20347 (10)	0.18840 (18)	0.93540 (16)	0.0292 (3)
H10A	1.2101	0.2003	1.0389	0.044*
H10B	1.2620	0.2312	0.9039	0.044*
H10C	1.1947	0.0694	0.9095	0.044*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0233 (5)	0.0140 (5)	0.0262 (5)	0.0037 (3)	0.0066 (4)	0.0002 (4)
O2	0.0337 (5)	0.0197 (5)	0.0184 (5)	−0.0009 (4)	0.0104 (4)	0.0022 (4)
O3	0.0213 (5)	0.0162 (4)	0.0226 (5)	−0.0066 (3)	0.0095 (4)	−0.0030 (4)
N1	0.0154 (5)	0.0146 (5)	0.0175 (5)	−0.0010 (4)	0.0030 (4)	−0.0002 (4)
C1	0.0152 (6)	0.0152 (6)	0.0133 (6)	0.0025 (5)	0.0021 (5)	0.0008 (5)
C2	0.0139 (6)	0.0155 (6)	0.0161 (6)	−0.0002 (5)	0.0016 (5)	0.0030 (5)
C3	0.0165 (6)	0.0125 (6)	0.0167 (6)	−0.0002 (4)	−0.0002 (5)	0.0005 (5)
C4	0.0201 (6)	0.0136 (6)	0.0200 (6)	−0.0031 (5)	0.0032 (5)	−0.0013 (5)
C5	0.0196 (6)	0.0166 (6)	0.0200 (6)	−0.0042 (5)	0.0038 (5)	0.0010 (5)
C6	0.0214 (7)	0.0212 (7)	0.0263 (7)	−0.0012 (5)	0.0069 (6)	0.0033 (5)
C7	0.0209 (7)	0.0252 (7)	0.0191 (7)	−0.0031 (5)	0.0041 (5)	0.0003 (5)
C8	0.0219 (7)	0.0253 (7)	0.0244 (7)	−0.0018 (5)	0.0060 (6)	−0.0024 (6)
C9	0.0214 (7)	0.0366 (8)	0.0215 (7)	−0.0039 (6)	0.0050 (6)	−0.0019 (6)
C10	0.0220 (7)	0.0349 (8)	0.0319 (8)	−0.0012 (6)	0.0079 (6)	−0.0063 (6)

Geometric parameters (Å, º) top

O1—N1	1.2268 (12)	C6—C7	1.5247 (16)
O2—N1	1.2269 (12)	C6—H6A	0.9900
O3—C2	1.3549 (13)	C6—H6B	0.9900
O3—C4	1.4438 (14)	C7—C8	1.5191 (18)
N1—C1	1.4682 (14)	C7—H7A	0.9900
C1—C3ⁱ	1.3803 (16)	C7—H7B	0.9900
C1—C2	1.3983 (16)	C8—C9	1.5196 (17)
C2—C3	1.3862 (16)	C8—H8A	0.9900
C3—C1ⁱ	1.3804 (16)	C8—H8B	0.9900
C3—H3	0.9500	C9—C10	1.5218 (19)
C4—C5	1.5097 (16)	C9—H9A	0.9900
C4—H4A	0.9900	C9—H9B	0.9900
C4—H4B	0.9900	C10—H10A	0.9800
C5—C6	1.5223 (17)	C10—H10B	0.9800
C5—H5A	0.9900	C10—H10C	0.9800
C5—H5B	0.9900

C2—O3—C4	117.53 (9)	C5—C6—H6B	108.7
O2—N1—O1	123.94 (10)	C7—C6—H6B	108.7
O2—N1—C1	118.47 (9)	H6A—C6—H6B	107.6
O1—N1—C1	117.57 (9)	C8—C7—C6	112.28 (10)
C3ⁱ—C1—C2	123.36 (10)	C8—C7—H7A	109.1
C3ⁱ—C1—N1	116.43 (10)	C6—C7—H7A	109.1
C2—C1—N1	120.21 (10)	C8—C7—H7B	109.1
O3—C2—C3	124.83 (11)	C6—C7—H7B	109.1
O3—C2—C1	118.22 (10)	H7A—C7—H7B	107.9
C3—C2—C1	116.94 (10)	C9—C8—C7	114.90 (11)
C1ⁱ—C3—C2	119.70 (11)	C9—C8—H8A	108.5
C1ⁱ—C3—H3	120.1	C7—C8—H8A	108.5
C2—C3—H3	120.1	C9—C8—H8B	108.5
O3—C4—C5	106.69 (9)	C7—C8—H8B	108.5
O3—C4—H4A	110.4	H8A—C8—H8B	107.5
C5—C4—H4A	110.4	C8—C9—C10	112.67 (12)
O3—C4—H4B	110.4	C8—C9—H9A	109.1
C5—C4—H4B	110.4	C10—C9—H9A	109.1
H4A—C4—H4B	108.6	C8—C9—H9B	109.1
C4—C5—C6	112.80 (10)	C10—C9—H9B	109.1
C4—C5—H5A	109.0	H9A—C9—H9B	107.8
C6—C5—H5A	109.0	C9—C10—H10A	109.5
C4—C5—H5B	109.0	C9—C10—H10B	109.5
C6—C5—H5B	109.0	H10A—C10—H10B	109.5
H5A—C5—H5B	107.8	C9—C10—H10C	109.5
C5—C6—C7	114.44 (10)	H10A—C10—H10C	109.5
C5—C6—H6A	108.7	H10B—C10—H10C	109.5
C7—C6—H6A	108.7

O2—N1—C1—C3ⁱ	136.39 (11)	N1—C1—C2—C3	178.96 (10)
O1—N1—C1—C3ⁱ	−41.95 (14)	O3—C2—C3—C1ⁱ	−178.21 (11)
O2—N1—C1—C2	−43.17 (15)	C1—C2—C3—C1ⁱ	0.53 (18)
O1—N1—C1—C2	138.49 (11)	C2—O3—C4—C5	172.90 (10)
C4—O3—C2—C3	2.00 (17)	O3—C4—C5—C6	−67.13 (13)
C4—O3—C2—C1	−176.73 (10)	C4—C5—C6—C7	−171.07 (11)
C3ⁱ—C1—C2—O3	178.27 (11)	C5—C6—C7—C8	174.35 (11)
N1—C1—C2—O3	−2.21 (16)	C6—C7—C8—C9	−177.18 (11)
C3ⁱ—C1—C2—C3	−0.56 (19)	C7—C8—C9—C10	174.81 (11)

Symmetry code: (i) −x+1, −y, −z+2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3···O2ⁱⁱ	0.95	2.50	3.4525 (15)	179
C4—H4B···O1ⁱⁱⁱ	0.99	2.53	3.2852 (15)	133

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

Experimental details

Crystal data
Chemical formula	C₂₀H₃₂N₂O₆
M_r	396.48
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	13.988 (2), 7.9454 (13), 9.5344 (15)
β (°)	99.786 (3)
V (Å³)	1044.3 (3)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	0.09
Crystal size (mm)	0.40 × 0.40 × 0.25

Data collection
Diffractometer	Bruker SMART CCD area-detector diffractometer
Absorption correction	–
No. of measured, independent and observed [I > 2σ(I)] reflections	5776, 2110, 1733
R_int	0.035
(sin θ/λ)_max (Å⁻¹)	0.623

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.035, 0.093, 1.03
No. of reflections	2110
No. of parameters	128
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.24, −0.19

Computer programs: SMART (Bruker, 2001), SAINT (Bruker, 2002), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3···O2ⁱ	0.95	2.50	3.4525 (15)	179
C4—H4B···O1ⁱⁱ	0.99	2.53	3.2852 (15)	133

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

Acknowledgements

The authors would like to thank Dr Michael G. Hutchings for inspiration, and Dystar UK Ltd and the University of Manchester for funding.

References

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