Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010402462X/hj1027sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S010827010402462X/hj1027Isup2.hkl |
CCDC reference: 257031
A mixture of 2,3,6,7-tetrahydroxy-9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene (Davidson & Musgrave, 1963; 149 mg, 0.50 mmol), 2,3-dichloroquinoxaline (199 mg, 0.10 mmol) and anhydrous Cs2CO3 (900 mg, 2.8 mmol) in acetonitrile (11 ml) was stirred and boiled under a nitrogen atmosphere for 60 h. Extraction with chloroform, followed by column chromatography on silica gel with chloroform as eluent, afforded the pure product, (I) (yield 60 mg, 22%, m.p. > 633 K), from ethyl acetate. Analysis: 1H NMR (CDCl3, 300 MHz, δ, p.p.m.): 1.66 (s, 4H), 1.93 (s, 6H), 7.03 (s, 4H), 7.57 (dd, 4H, J = 6.0 Hz, J' = 3.5 Hz), 7.79 (dd, 4H, J = 6.0 Hz, J' = 3.5 Hz); 13C NMR (Solvent?, Frequency?, δ, p.p.m.): 18.3, 35.4, 41.4, 110.1, 127.2, 128.8, 138.0, 139.1, 143.0, 144.9. Single crystals were obtained by slow evaporation of an ethyl acetate solution of compound (I).
All H atoms were introduced in calculated positions as riding atoms, with C–H distances of 0.93 (CH), 0.97 (CH2) and 0.96 Å (CH3), and with Uiso(H) = 1.2 (CH or CH2) or 1.5 (CH3) times Ueq of the parent atom.
Data collection: KappaCCD Server Software (Nonius, 1997); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1999); software used to prepare material for publication: SHELXTL and PLATON (Spek, 2003).
C34H22N4O4 | F(000) = 1144 |
Mr = 550.56 | Dx = 1.453 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -C 2yc | Cell parameters from 9551 reflections |
a = 26.055 (2) Å | θ = 3.1–25.7° |
b = 6.6734 (12) Å | µ = 0.10 mm−1 |
c = 14.523 (2) Å | T = 100 K |
β = 94.788 (8)° | Needle, colourless |
V = 2516.4 (6) Å3 | 0.15 × 0.05 × 0.05 mm |
Z = 4 |
Nonius KappaCCD area-detector diffractometer | 1196 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.075 |
Graphite monochromator | θmax = 25.7°, θmin = 3.1° |
ϕ scans | h = −31→31 |
9551 measured reflections | k = −8→0 |
2358 independent reflections | l = −17→17 |
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)] = 0.064 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.167 | H-atom parameters constrained |
S = 1.03 | w = 1/[σ2(Fo2) + (0.0584P)2 + 0.367P] where P = (Fo2 + 2Fc2)/3 |
2358 reflections | (Δ/σ)max < 0.001 |
191 parameters | Δρmax = 0.24 e Å−3 |
0 restraints | Δρmin = −0.31 e Å−3 |
C34H22N4O4 | V = 2516.4 (6) Å3 |
Mr = 550.56 | Z = 4 |
Monoclinic, C2/c | Mo Kα radiation |
a = 26.055 (2) Å | µ = 0.10 mm−1 |
b = 6.6734 (12) Å | T = 100 K |
c = 14.523 (2) Å | 0.15 × 0.05 × 0.05 mm |
β = 94.788 (8)° |
Nonius KappaCCD area-detector diffractometer | 1196 reflections with I > 2σ(I) |
9551 measured reflections | Rint = 0.075 |
2358 independent reflections |
R[F2 > 2σ(F2)] = 0.064 | 0 restraints |
wR(F2) = 0.167 | H-atom parameters constrained |
S = 1.03 | Δρmax = 0.24 e Å−3 |
2358 reflections | Δρmin = −0.31 e Å−3 |
191 parameters |
Experimental. A 180° range in ϕ was scanned during both data collections, with 2° ϕ steps. Crystal-to-detector distance fixed at 28 mm. |
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. Structure solved by direct methods and subsequent Fourier-difference synthesis. All non-hydrogen atoms were refined with anisotropic displacement parameters. The H atoms were introduced at calculated positions and were treated as riding atoms with an isotropic displacement parameter equal to 1.2 (CH, CH2) or 1.5 (CH3) times that of the parent atom. 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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.18017 (8) | 0.0978 (4) | −0.13949 (14) | 0.0266 (6) | |
O2 | 0.12149 (8) | 0.0796 (4) | 0.01815 (14) | 0.0269 (6) | |
N1 | 0.25173 (10) | 0.0208 (4) | −0.04899 (18) | 0.0233 (7) | |
N2 | 0.19321 (11) | −0.0049 (4) | 0.10649 (18) | 0.0259 (7) | |
C1 | 0.12763 (12) | 0.1411 (5) | −0.1456 (2) | 0.0233 (8) | |
C2 | 0.09975 (13) | 0.1362 (5) | −0.0690 (2) | 0.0235 (8) | |
C3 | 0.04854 (13) | 0.1963 (5) | −0.0763 (2) | 0.0257 (9) | |
H3 | 0.0295 | 0.1912 | −0.0250 | 0.031* | |
C4 | 0.02583 (12) | 0.2639 (5) | −0.1603 (2) | 0.0245 (8) | |
C5 | 0.05467 (12) | 0.2651 (6) | −0.2383 (2) | 0.0254 (8) | |
C6 | 0.10527 (13) | 0.2014 (5) | −0.2309 (2) | 0.0240 (8) | |
H6 | 0.1241 | 0.1991 | −0.2826 | 0.029* | |
C7 | 0.20290 (13) | 0.0527 (5) | −0.0539 (2) | 0.0231 (8) | |
C8 | 0.17349 (13) | 0.0409 (5) | 0.0257 (2) | 0.0221 (8) | |
C9 | 0.24545 (13) | −0.0446 (6) | 0.1144 (2) | 0.0242 (8) | |
C10 | 0.27463 (13) | −0.0305 (5) | 0.0368 (2) | 0.0229 (8) | |
C11 | 0.32778 (13) | −0.0722 (5) | 0.0461 (2) | 0.0252 (8) | |
H11 | 0.3470 | −0.0623 | −0.0048 | 0.030* | |
C12 | 0.35105 (14) | −0.1274 (6) | 0.1305 (2) | 0.0282 (9) | |
H12 | 0.3861 | −0.1558 | 0.1365 | 0.034* | |
C13 | 0.32222 (14) | −0.1415 (6) | 0.2084 (2) | 0.0291 (9) | |
H13 | 0.3384 | −0.1785 | 0.2654 | 0.035* | |
C14 | 0.27052 (13) | −0.1009 (6) | 0.2004 (2) | 0.0279 (9) | |
H14 | 0.2518 | −0.1105 | 0.2520 | 0.034* | |
C15 | −0.02690 (13) | 0.3620 (6) | −0.1770 (2) | 0.0259 (9) | |
C16 | −0.01518 (14) | 0.5816 (6) | −0.2062 (2) | 0.0303 (9) | |
H16A | −0.0472 | 0.6543 | −0.2188 | 0.036* | |
H16B | 0.0049 | 0.6489 | −0.1561 | 0.036* | |
C17 | −0.05871 (13) | 0.3620 (6) | −0.0928 (2) | 0.0293 (9) | |
H17A | −0.0659 | 0.2264 | −0.0759 | 0.044* | |
H17B | −0.0905 | 0.4320 | −0.1077 | 0.044* | |
H17C | −0.0396 | 0.4276 | −0.0420 | 0.044* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0225 (13) | 0.0350 (16) | 0.0226 (12) | 0.0036 (12) | 0.0033 (10) | 0.0025 (11) |
O2 | 0.0218 (13) | 0.0395 (17) | 0.0196 (12) | 0.0027 (12) | 0.0026 (10) | 0.0011 (11) |
N1 | 0.0213 (16) | 0.0265 (18) | 0.0229 (15) | −0.0010 (13) | 0.0061 (13) | 0.0016 (13) |
N2 | 0.0231 (16) | 0.0294 (18) | 0.0261 (16) | −0.0015 (14) | 0.0069 (13) | 0.0002 (13) |
C1 | 0.0186 (18) | 0.026 (2) | 0.0260 (19) | 0.0018 (16) | 0.0076 (15) | −0.0013 (16) |
C2 | 0.0249 (19) | 0.029 (2) | 0.0177 (17) | −0.0021 (16) | 0.0042 (15) | −0.0008 (16) |
C3 | 0.0237 (19) | 0.029 (2) | 0.0253 (18) | −0.0026 (16) | 0.0088 (15) | −0.0021 (16) |
C4 | 0.0220 (19) | 0.027 (2) | 0.0246 (18) | −0.0017 (17) | 0.0019 (15) | −0.0033 (16) |
C5 | 0.0193 (18) | 0.030 (2) | 0.0277 (19) | −0.0004 (17) | 0.0068 (15) | −0.0007 (17) |
C6 | 0.0250 (19) | 0.025 (2) | 0.0228 (18) | −0.0019 (16) | 0.0068 (14) | −0.0008 (15) |
C7 | 0.027 (2) | 0.023 (2) | 0.0191 (17) | −0.0025 (16) | 0.0040 (15) | 0.0021 (15) |
C8 | 0.0215 (18) | 0.022 (2) | 0.0234 (18) | −0.0001 (15) | 0.0050 (15) | 0.0002 (15) |
C9 | 0.0226 (19) | 0.028 (2) | 0.0224 (18) | 0.0001 (16) | 0.0062 (15) | −0.0017 (15) |
C10 | 0.0238 (19) | 0.022 (2) | 0.0226 (18) | −0.0028 (16) | 0.0007 (15) | −0.0022 (15) |
C11 | 0.027 (2) | 0.026 (2) | 0.0238 (18) | −0.0024 (17) | 0.0113 (15) | −0.0012 (16) |
C12 | 0.025 (2) | 0.030 (2) | 0.0304 (19) | 0.0017 (17) | 0.0039 (16) | 0.0007 (17) |
C13 | 0.028 (2) | 0.032 (2) | 0.0275 (19) | −0.0020 (17) | −0.0004 (16) | 0.0044 (17) |
C14 | 0.029 (2) | 0.032 (2) | 0.0236 (18) | −0.0057 (17) | 0.0083 (16) | −0.0019 (16) |
C15 | 0.0222 (19) | 0.033 (2) | 0.0234 (18) | 0.0035 (17) | 0.0071 (14) | −0.0042 (16) |
C16 | 0.029 (2) | 0.032 (2) | 0.0299 (19) | 0.0039 (19) | 0.0051 (16) | −0.0032 (18) |
C17 | 0.026 (2) | 0.039 (2) | 0.0240 (18) | 0.0023 (17) | 0.0085 (15) | −0.0043 (17) |
O1—C1 | 1.395 (4) | C9—C10 | 1.413 (5) |
O1—C7 | 1.364 (4) | C10—C11 | 1.408 (4) |
O2—C2 | 1.395 (4) | C11—C12 | 1.372 (4) |
O2—C8 | 1.375 (4) | C11—H11 | 0.9300 |
N1—C7 | 1.286 (4) | C12—C13 | 1.413 (5) |
N1—C10 | 1.380 (4) | C12—H12 | 0.9300 |
N2—C8 | 1.278 (4) | C13—C14 | 1.370 (5) |
N2—C9 | 1.382 (4) | C14—C9 | 1.412 (4) |
C1—C2 | 1.379 (4) | C13—H13 | 0.9300 |
C2—C3 | 1.389 (4) | C14—H14 | 0.9300 |
C3—C4 | 1.386 (5) | C15—C5i | 1.519 (4) |
C3—H3 | 0.9300 | C15—C16 | 1.563 (5) |
C4—C5 | 1.410 (5) | C15—C17 | 1.533 (5) |
C5—C6 | 1.381 (4) | C16—C16i | 1.553 (7) |
C6—C1 | 1.385 (4) | C16—H16A | 0.9700 |
C4—C15 | 1.523 (4) | C16—H16B | 0.9700 |
C5—C15i | 1.519 (4) | C17—H17A | 0.9600 |
C6—H6 | 0.9300 | C17—H17B | 0.9600 |
C7—C8 | 1.442 (5) | C17—H17C | 0.9600 |
C7—O1—C1 | 116.9 (3) | N1—C10—C9 | 121.0 (3) |
C8—O2—C2 | 116.5 (3) | C11—C10—C9 | 120.1 (3) |
C7—N1—C10 | 116.3 (3) | C12—C11—C10 | 119.8 (3) |
C8—N2—C9 | 116.1 (3) | C12—C11—H11 | 120.1 |
C2—C1—C6 | 121.2 (3) | C10—C11—H11 | 120.1 |
C2—C1—O1 | 121.6 (3) | C11—C12—C13 | 120.6 (3) |
C6—C1—O1 | 117.0 (3) | C11—C12—H12 | 119.7 |
C1—C2—C3 | 119.9 (3) | C13—C12—H12 | 119.7 |
C1—C2—O2 | 122.5 (3) | C14—C13—C12 | 120.3 (3) |
C3—C2—O2 | 117.5 (3) | C14—C13—H13 | 119.9 |
C4—C3—C2 | 119.9 (3) | C12—C13—H13 | 119.9 |
C4—C3—H3 | 120.1 | C13—C14—C9 | 120.5 (3) |
C2—C3—H3 | 120.1 | C13—C14—H14 | 119.8 |
C3—C4—C5 | 119.4 (3) | C9—C14—H14 | 119.8 |
C3—C4—C15 | 126.3 (3) | C4—C15—C5i | 107.9 (3) |
C5—C4—C15 | 113.9 (3) | C5i—C15—C17 | 113.2 (3) |
C6—C5—C4 | 120.4 (3) | C4—C15—C17 | 114.5 (3) |
C6—C5—C15i | 125.5 (3) | C4—C15—C16 | 104.6 (3) |
C4—C5—C15i | 113.8 (3) | C5i—C15—C16 | 105.6 (3) |
C5—C6—C1 | 119.1 (3) | C17—C15—C16 | 110.3 (3) |
C5—C6—H6 | 120.5 | C16i—C16—C15 | 110.31 (17) |
C1—C6—H6 | 120.5 | C16i—C16—H16A | 109.6 |
N1—C7—O1 | 116.1 (3) | C15—C16—H16A | 109.6 |
N1—C7—C8 | 122.4 (3) | C16i—C16—H16B | 109.6 |
O1—C7—C8 | 121.5 (3) | C15—C16—H16B | 109.6 |
N2—C8—O2 | 115.8 (3) | H16A—C16—H16B | 108.1 |
N2—C8—C7 | 123.4 (3) | C15—C17—H17A | 109.5 |
O2—C8—C7 | 120.8 (3) | C15—C17—H17B | 109.5 |
N2—C9—C14 | 120.3 (3) | H17A—C17—H17B | 109.5 |
N2—C9—C10 | 120.8 (3) | C15—C17—H17C | 109.5 |
C14—C9—C10 | 118.9 (3) | H17A—C17—H17C | 109.5 |
N1—C10—C11 | 118.9 (3) | H17B—C17—H17C | 109.5 |
Symmetry code: (i) −x, y, −z−1/2. |
Experimental details
Crystal data | |
Chemical formula | C34H22N4O4 |
Mr | 550.56 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 100 |
a, b, c (Å) | 26.055 (2), 6.6734 (12), 14.523 (2) |
β (°) | 94.788 (8) |
V (Å3) | 2516.4 (6) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.10 |
Crystal size (mm) | 0.15 × 0.05 × 0.05 |
Data collection | |
Diffractometer | Nonius KappaCCD area-detector diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 9551, 2358, 1196 |
Rint | 0.075 |
(sin θ/λ)max (Å−1) | 0.610 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.064, 0.167, 1.03 |
No. of reflections | 2358 |
No. of parameters | 191 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.24, −0.31 |
Computer programs: KappaCCD Server Software (Nonius, 1997), DENZO-SMN (Otwinowski & Minor, 1997), DENZO-SMN, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL (Bruker, 1999), SHELXTL and PLATON (Spek, 2003).
O1—C1 | 1.395 (4) | C6—C1 | 1.385 (4) |
O1—C7 | 1.364 (4) | C4—C15 | 1.523 (4) |
O2—C2 | 1.395 (4) | C5—C15i | 1.519 (4) |
O2—C8 | 1.375 (4) | C7—C8 | 1.442 (5) |
N1—C7 | 1.286 (4) | C9—C10 | 1.413 (5) |
N1—C10 | 1.380 (4) | C10—C11 | 1.408 (4) |
N2—C8 | 1.278 (4) | C11—C12 | 1.372 (4) |
N2—C9 | 1.382 (4) | C12—C13 | 1.413 (5) |
C1—C2 | 1.379 (4) | C13—C14 | 1.370 (5) |
C2—C3 | 1.389 (4) | C14—C9 | 1.412 (4) |
C3—C4 | 1.386 (5) | C15—C16 | 1.563 (5) |
C4—C5 | 1.410 (5) | C15—C17 | 1.533 (5) |
C5—C6 | 1.381 (4) | C16—C16i | 1.553 (7) |
C3—C4—C15 | 126.3 (3) | C4—C15—C5i | 107.9 (3) |
C5—C4—C15 | 113.9 (3) | C4—C15—C16 | 104.6 (3) |
C6—C5—C15i | 125.5 (3) | C5i—C15—C16 | 105.6 (3) |
C4—C5—C15i | 113.8 (3) | C16i—C16—C15 | 110.31 (17) |
Symmetry code: (i) −x, y, −z−1/2. |
We have previously reported the first crystal structure of a compound containing the tetrahydroxydihydroethanoanthracene unit, namely 2,3,6,7-tetrahydroxy-9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene bis(1,4-dioxane) solvate, (II) (Masci et al., 2002), as well as the structure of the octanuclear uranyl complex, (III), obtained from the corresponding tetra-catecholate species (Thuéry & Masci, 2003). The compound described here, (I), is built from the same central unit. \sch
The asymmetric unit in (I) contains half a molecule, the other half being generated by the twofold axis bisecting the ethane bridge (Fig. 1). The dihedral angle between the two aromatic rings bound to the central curved part of the molecule is 138.88 (8)°, larger than in (II) [130.61 (4)°] and (III) [100.9 (6)°], the large deviation in (III) being due to the strains induced by uranyl coordination to form a cyclic assemblage. The dihedral angles between the same aromatic rings and the plane defined by atoms C15, C16 and their symmetry equivalents is 110.54 (9)° [114.64 (4)° in (II)]. A search of the Cambridge Structural Database (CSD, Version 5.25; Allen, 2002) for structures containing the dihydroethanoanthracene fragment shows that these dihedral angles span very wide ranges, 108.1–133.2° [mean value 123 (5)°] between the two aromatic rings and 110.4–131.1° [mean value 118 (4)°] between the aromatic rings and the central plane. In the simplest compound in this family, 9,10-dihydro-9,10-ethanoanthracene (or [2,3:5,6]dibenzo[2.2.2]octa-2,5-diene), (IV) (Burrows et al., 1999), these angles are 124.7 and 118.3° (mean value), respectively. Thus, it appears that the shape of (I) is much flatter than any other in this family of compounds. This could be an effect of the intermolecular interactions governing the packing (see below). However, larger dihedral angles between the aromatic rings are encountered in systems in which the ethane bridge is absent, for example in compounds containing the tetramethoxydihydroanthracene fragment [151.7° (Benetollo et al., 1990) and 153.3° (Guy et al., 1996)].
The fused dioxin and three aromatic rings of (I) are coplanar, with an r.m.s. deviation of 0.063 Å. The maximum out-of-plane displacements are observed for atoms C4, C1 and C5 [0.145 (3), −0.091 (3) and 0.090 (3) Å, respectively]; these atoms pertain to the aromatic ring bound to the central cyclohexane ring, which may indicate the strains in this part of the molecule related to the rather large dihedral angle indicated above. The two O atoms are also associated with rather large out-of-plane displacements, of −0.088 (3) and −0.080 (3) Å, whereas the displacements of the remaining atoms do not exceed 0.06 Å. The dioxin ring is nearly planar (r.m.s. deviation 0.016 Å), as is usual when it is fused to two aromatic rings. The interatomic distances in the C1–C6 aromatic ring show the same (and even more pronounced) trend as in (II) and (IV), with the C1–C2 bond length being shorter than C4–C5 by 0.031 Å (Table 1) [0.015 and 0.020 Å in (II) and (IV), respectively].
The bond lengths in the pyrazine ring are also somewhat irregular, with differences of 0.029 Å between C7–C8 and C9–C10, and of 0.099 Å (mean value) between the bond lengths on each side of both N1 and N2. In the terminal aromatic ring, C9–C14, the C11–C12 and C13–C14 bond lengths are shorter than the others by 0.041 Å (mean value). In the dioxin ring, the distances around atoms O1 and O2 are also non-symmetric, with a difference of 0.025 Å (mean value).
It may be noted that no other example of a compound containing such fused dioxin and pyrazine rings is present in the CSD, although the structures of three compounds with planar fused dioxin and pyridine rings have been reported (Piórko Christie et al., 1994; Piórko Christie & Zaworotko, 1994; Troya et al., 2002). As in compounds (II) and (IV), the geometry of the central bicyclic system in (I) evidences its strained nature. The rather long C15–C16 and C16–C16' bonds are comparable with their counterparts in (II) and (IV) [primed atoms are at the symmetry position (-x, y, −1/2 − z)]. The `exterior' angles C3–C4–C15 and C6–C5–C15' [mean value 125.9 (6)°] are much larger than the `interior' angles C4–C5–C15' and C5–C4–C15 [mean value 113.9 (7)°].
The packing in (I) brings upside-down molecules into close contact, albeit slightly offset, indicating the presence of π–π interactions (Fig. 2). The pyrazine ring is involved in two such contacts. One of them involves the terminal aromatic ring of the molecule related by the symmetry operation (1/2 − x, −1/2 − y, −z) [centroid–centroid distance 3.590 (2) Å, mean interplanar spacing 3.22 (2) Å, mean centroid offset 1.59 Å, dihedral angle 1.2° and shortest interatomic contact 3.30 Å, which is shorter than twice the out-of-plane van der Waals radius of a C atom (1.7 Å)]. The other involves the parallel pyrazine counterpart in the neighbouring molecule at (1/2 − x, 1/2 − y,-z) [centroid–centroid distance 3.673 (2) Å, interplanar spacing 3.22 Å, centroid offset 1.77 Å and shortest interatomic contact 3.25 Å]. Each molecule is thus linked to four of its neighbours and infinite sheets of molecules parallel to the (101) plane are thus formed, successive sheets being held together by van der Waals interactions.