(E)-4,4′-Bis(1,3-benzoxazol-2-yl)stilbene at 150 and 375 K

The title compound, a chromophore of formula C₂₈H₁₈N₂O₂, crystallizes with the mol­ecule lying on an inversion centre to give one-half of a crystallographically independent mol­ecule in the asymmetric unit. The mol­ecule is almost planar, with slight deviation of the benzene rings from the mean mol­ecular plane. The structure is characterized by a herringbone packing arrangement arising from C—H...π and π–π inter­molecular inter­actions. The benzoxazole group is disordered between two orientations, with occupancy factors of 0.669 (10) and 0.331 (10) at 150 K [0.712 (7) and 0.288 (7) at 375 K].

S1. Comment

The title compound, (I), hereinafter denoted BBS, belongs to the well known class of stilbenes where conjugation between the two phenyl groups allows UV excitation to induce conversion between the E and Z isomers, making these compounds useful as photoactive switches (Irie, 2000; Momotake & Arai, 2004). This compound is generally employed as a fluorescent brightener in textiles (Bischoff et al., 2001), detergents and other materials (Bur & Roth, 2004). It is also used as an additive for food and consumer packaging materials, due to its compliance with the US Food and Drug Administration regulations (Jervis, 2003). In addition, BBS has applications in host–guest systems as a molecular probe of deformation and temperature in polymer films (Pucci et al., 2005, 2007; Sing et al., 2009). The anisotropic flat shape of the molecule can be exploited to produce polarized light by adding the chromophore to oriented macromolecular matrices (Pucci et al., 2006).

Fig. 1 shows the fluorescence spectrum of BBS diluted in poly(1,4-butylene succinate) (PBS) at various concentrations, similar to data reported by Pucci et al. (2007). At low concentrations, the fluorescence spectra resemble the spectrum of BBS in tetrachloroethane solution (Pucci et al., 2005, 2007), with emission bands centred at 410, 434 and 464 nm. These spectra are associated with isolated BBS monomers molecularly dispersed in the amorphous phase of PBS. Increasing the BBS concentration from 0.02 to 0.2 wt% induces the emergence of a broad emission band centred at about 500 nm, and is accompanied by a colour change from blue to green. The broad band is attributed to the formation of BBS aggregates, favoured by π–π interactions of BBS molecules in planar conformation, thus allowing excimer emission (Pucci et al., 2005, 2007).

For more precise information on BBS stacking characteristics, we report here the single-crystal structure of BBS crystallized from a solution of 1,2-dichlorobenzene. The inset in Fig. 1 shows that the fluorescence spectrum of the yellow bulk powder displays only the broad band centred at about 500 nm and none of the three bands characteristic of isolated BBS molecules. This indicates that the powder is composed only of excimer-forming aggregates. The latter can be assumed to have the same structure as in the PBS films, as supported by the observation that the X-ray powder diffraction pattern of the bulk sample is consistent with the calculated pattern obtained from the experimental single-crystal data. This allows a correlation to be made between the single-crystal structure of BBS and excimer emission in BBS-containing films.

From the single-crystal structure analysis at 150 K, it is found that the molecule of (I) is almost planar and lies on an inversion centre located at the mid-point of the C═C bond (Fig. 2). The mean planes of the central phenyl rings and the central alkene are twisted by 6.66 (13)°, but the angle between the phenyl rings and the benzoxazolyl groups is only 2.30 (16)°. Moreover, the structure of (I) features a network composed of layers in the bc plane, with molecules packed in a well defined herring-bone pattern (Fig. 3), similar to that of stilbene (Harada & Ogawa, 2001, 2004), but unlike other stilbene derivatives (Foitzik et al., 1991; Ohba et al., 2002; Soto Bustamante et al., 1995).

Within the layers, the flat molecules are packed via π–π stacking interactions and C—H···π contacts. The π–π stacking interactions feature a short distance of 3.6565 (7) Å between centroids Cg3 of the central phenyl ring and Cg4ⁱⁱ of the terminal phenyl ring, with a dihedral angle of 2.28 (6)° between ring planes [symmetry code: (ii) x, y - 1, z]. The π-stacked molecules are staggered relative to one another and the phenyl rings overlap at a perpendicular distance of 3.3914 (5) Å. Moreover, a C—H···π contact (Fig. 3) involves atom H12, with a distance to the terminal phenyl ring centroid Cg4ⁱⁱⁱ of 2.77 (1) Å [symmetry code: (iii) 3/2 - x, 1/2 + y, 1/2 - z].

trans-Stilbenes and diazobenzenes are known to be subject to orientational disorder, described as a pedal-like motion wherein the pair of benzene rings rotates around the central double bond like a bicycle pedal (Harada & Ogawa, 2001; Bouwstra et al., 1984). This disorder is dynamic with interconversion between the major and minor conformers, the relative populations of which vary with temperature. At lower temperatures, the low occupancy factor of the minor conformer can make the disorder almost invisible (Harada & Ogawa, 2004). Usually, this disorder is detected by a shortening of the central double bond (Masciocchi et al., 2005) and by the appearance in the final Fourier difference map of two residual peaks in the vicinity of the central double bond that arise from the minor conformer (Harada & Ogawa, 2001, 2004). This was examined for (I) by measuring two different single crystals grown from the same solution, one at 150 K and the other at 375 K. The distance of the central C1═C1ⁱ double bond is 1.331 (2) Å at 150 K and 1.306 (2) Å at 375 K [symmetry code: (i) 3/2 - x, -y - 1/2, -z Please check]. At 150 K, the value compares well with the normal expected value for a double bond, and the difference Fourier map calculated after the final refinement of (I) (Spek, 2009) did not reveal any significant residual peaks in the region of the C═C bond. At 375 K, the central double bond is significantly shorter than expected but no residual peaks were detected in the final difference Fourier map. This may indicate that at 375 K the crystal is near the onset of dynamic disorder.

On the other hand, disorder related to the benzoxazolyl moiety was detected by the checkCIF (Spek, 2009) procedure performed at the end of the refinement. Two bonds, N1—C8 and O1—C10, failed the Hirshfeld difference test (Hirshfeld, 1976), with a very large s.u. of 15 for N1—C8. Examination of the final atomic displacement ellipsoid plot showed that the ellipsoids for atoms N1 and O1 are smaller and larger, respectively, than the other atoms of the molecule. These features were attributed to a substitutional disorder between O and N atoms sharing the same position. Such a statistical disorder in benzoxazolyl derivatives has been described previously (Norman et al., 2002; Zhuang et al., 2002). The occupancy factors of the N and O atoms were refined, giving a ratio of 0.66:0.34 between the two possible conformations for the crystal measured at 150 K.

The single-crystal structure of BBS confirms that the BBS molecules have an essentially planar conformation with extensive π–π stacking interactions that allow for excimer formation, giving rise to the emission band centred at 500 nm. More specifically, the molecules are packed into a two-dimensional herring-bone network, held together by intermolecular π–π and C—H···π interactions. The perpendicular distance of 3.46 Å and the centroid distances of 3.6–3.7 Å between π-stacked molecules are very close to the pyrene interplanar stacking of 3.53 Å (Gilbert & Baggott, 1991). This distance is within the range of 3–4 Å that is considered necessary for excimer formation to take place (Gilbert & Baggott, 1991).

S2. Experimental

4,4'-Bis(1,3-benzoxazol-2-yl)stilbene (BBS) was obtained from Aldrich (97%, m.p. > 573 K) and used without further purification. Yellow needle-like crystals of BBS, (I), suitable for X-ray diffraction analysis were obtained by slow evaporation from a solution in 1,2-dichlorobenzene.

Poly(1,4-butylene succinate) (PBS) (Bionolle 1001) was obtained from Showa Highpolymer (Japan). PBS–BBS blends were prepared by melt-processing in a Plasti-Corder Brabender mixer, type DDRV501/DIGI-SYS, using 20 g of the polymer and 0.02–0.2 wt.% of the chromophore. Films with a thickness of about 80–120 µm were obtained by compression-moulding between two aluminium foils in a Carver Laboratory Press at 473 K, followed by slow cooling to room temperature. Fluorescence emission spectra were recorded at ambient temperature using an Edinburgh Instruments FLS-920 fluorimeter, operating at an excitation wavelength of 377 nm.

S3. Refinement

The initial unit-cell parameters were determined by a least-squares fit of the angular setting of strong reflections, collected by a 10.0° scan in 33 frames over three different parts of the reciprocal space. The final unit cell was obtained from the xyz centroids of 7849 selected reflections at 150 K (4605 reflections at 375 K) after integration using the SAINT-Plus software package (Bruker, 2009).

H atoms were positioned geometrically and refined with a riding model, with C—H = 0.95 Å and U_iso(H) = 1.2U_eq(C).

The benzoxazolyl group shows orientational disorder. It was assumed that atoms N1A and O1B, and atoms O1A and N1B, share close positions and the same atomic displacement parameters. Refinement was carried out using restraints on C—N and C—O distances following the SADI and EADP instructions in SHELX97 (Sheldrick, 2008). With these restraints, the occupancy factors converged to 0.669 (10) and 0.331 (10) for N1A and O1B, respectively, for the crystal measured at 150 K.

For the crystal measured at 375 K, analysis of the refined solution using PLATON/TwinRotMat (Spek, 2009) indicated non-merohedral twinning about a twofold rotation axis (001). The TwinRotMat routine was used to prepare a modified hkl file for use with the HKLF5 option in SHELXL97 (Sheldrick, 2008). The resulting twin fractions were 0.1102 (16) and 0.8898 (16).

Computing details

For both compounds, data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and Material Studio (Accelrys, 2005); software used to prepare material for publication: UdMX (Maris, 2004) and publCIF (Westrip, 2009).

Figures

	Fig. 1. Fluorescence spectra of BBS molecules dispersed at various concentrations (wt.%) in polybutylene succinate films normalized relative to the peak at 410 nm. Inset: fluorescence spectrum of BBS pellets (compacted powder) containing only BBS aggregates.
	Fig. 2. The molecular structure of BBS at 150 K and 375 K, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. Only one part of the disordered benzoxazolyl ring is shown. [Symmetry code: (i) 3/2 - x, -y - 1/2, -z].
	Fig. 3. A view of the C—H···π and π–π stacking interactions (dotted lines) in one layer of π-stacked molecules of BBS at 150 K.

(I_150K) (E)-4,4'-Bis(1,3-benzoxazol-2-yl)stilbene

Crystal data

C28H18N2O2	F(000) = 864
Mr = 414.44	Dx = 1.411 Mg m^−3
Monoclinic, C2/c	Cu Kα radiation, λ = 1.54178 Å
Hall symbol: -C 2yc	Cell parameters from 7849 reflections
a = 11.2449 (4) Å	θ = 3.1–67.7°
b = 6.0053 (2) Å	µ = 0.71 mm^−1
c = 29.0699 (11) Å	T = 150 K
β = 96.4280 (17)°	Needle, yellow
V = 1950.72 (12) Å^3	0.28 × 0.04 × 0.03 mm
Z = 4

Data collection

Bruker Microstar diffractometer	1778 independent reflections
Radiation source: rotating anode	1606 reflections with I > 2σ(I)
Helios optics monochromator	Rint = 0.045
Detector resolution: 8.3 pixels mm^-1	θmax = 68.1°, θmin = 3.1°
ω scans	h = −13→13
Absorption correction: multi-scan (SADABS; Bruker, 2009)	k = −5→7
Tmin = 0.874, Tmax = 0.979	l = −34→34
17375 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.032	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.091	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0457P)^2 + 1.0947P] where P = (Fo^2 + 2Fc^2)/3
1778 reflections	(Δ/σ)max < 0.001
152 parameters	Δρmax = 0.21 e Å^−3
4 restraints	Δρmin = −0.15 e Å^−3

Special details

Experimental. X-ray crystallographic data for I were collected from a single-crystal sample, which was mounted on a loop fiber. Data were collected using a Bruker Microstar diffractometer equiped with a Platinum 135 CCD Detector, a Helios optics and a Kappa goniometer. The crystal-to-detector distance was 4.0 cm, and the data collection was carried out in 512 × 512 pixel mode. The initial unit-cell parameters were determined by a least-squares fit of the angular setting of strong reflections, collected by a 10.0 degree scan in 33 frames over three different parts of the reciprocal space (99 frames total).

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
C1	0.70388 (11)	−0.2125 (2)	0.01025 (4)	0.0310 (3)
H1	0.6318	−0.2958	0.0053	0.037*
C2	0.70240 (11)	−0.01447 (19)	0.03964 (4)	0.0283 (3)
C3	0.59417 (11)	0.0526 (2)	0.05470 (4)	0.0309 (3)
H3	0.5239	−0.0317	0.0458	0.037*
C4	0.58684 (11)	0.2389 (2)	0.08234 (4)	0.0298 (3)
H4	0.5122	0.2819	0.0920	0.036*
C5	0.68940 (11)	0.36286 (19)	0.09584 (4)	0.0272 (3)
C6	0.79834 (11)	0.2958 (2)	0.08159 (4)	0.0305 (3)
H6	0.8689	0.3784	0.0911	0.037*
C7	0.80464 (11)	0.1112 (2)	0.05392 (4)	0.0310 (3)
H7	0.8795	0.0686	0.0444	0.037*
C8	0.68404 (11)	0.55915 (19)	0.12471 (4)	0.0309 (3)
C9	0.62569 (10)	0.82678 (19)	0.16546 (4)	0.0267 (3)
C10	0.74851 (11)	0.84592 (19)	0.16490 (4)	0.0269 (3)
C11	0.81518 (11)	1.0152 (2)	0.18713 (4)	0.0311 (3)
H11	0.8992	1.0266	0.1863	0.037*
C12	0.75200 (11)	1.1676 (2)	0.21069 (4)	0.0330 (3)
H12	0.7939	1.2865	0.2268	0.040*
C13	0.62859 (12)	1.1507 (2)	0.21132 (4)	0.0331 (3)
H13	0.5885	1.2591	0.2277	0.040*
C14	0.56258 (11)	0.9804 (2)	0.18867 (4)	0.0319 (3)
H14	0.4784	0.9696	0.1891	0.038*
N1A	0.5897 (4)	0.6394 (13)	0.1385 (4)	0.0298 (7)	0.669 (10)
O1A	0.7880 (3)	0.6741 (12)	0.1391 (3)	0.0277 (7)	0.669 (10)
O1B	0.5818 (6)	0.644 (2)	0.1405 (6)	0.0277 (7)	0.331 (10)
N1B	0.7791 (7)	0.668 (3)	0.1371 (9)	0.0298 (7)	0.331 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0369 (6)	0.0261 (6)	0.0300 (6)	−0.0016 (5)	0.0040 (5)	0.0003 (5)
C2	0.0355 (6)	0.0250 (6)	0.0247 (6)	0.0019 (5)	0.0050 (5)	0.0026 (5)
C3	0.0324 (6)	0.0303 (6)	0.0303 (6)	−0.0029 (5)	0.0042 (5)	−0.0004 (5)
C4	0.0299 (6)	0.0301 (6)	0.0300 (6)	0.0029 (5)	0.0055 (5)	0.0002 (5)
C5	0.0331 (6)	0.0238 (6)	0.0247 (6)	0.0027 (5)	0.0035 (5)	0.0034 (5)
C6	0.0316 (6)	0.0282 (6)	0.0319 (6)	−0.0020 (5)	0.0044 (5)	0.0004 (5)
C7	0.0315 (6)	0.0294 (6)	0.0332 (6)	0.0032 (5)	0.0077 (5)	−0.0002 (5)
C8	0.0416 (7)	0.0241 (6)	0.0267 (6)	0.0010 (5)	0.0019 (5)	0.0035 (5)
C9	0.0305 (6)	0.0242 (6)	0.0251 (6)	0.0007 (5)	0.0022 (5)	0.0010 (4)
C10	0.0320 (6)	0.0233 (6)	0.0256 (6)	0.0025 (5)	0.0049 (5)	0.0016 (4)
C11	0.0299 (6)	0.0308 (6)	0.0326 (6)	−0.0030 (5)	0.0034 (5)	0.0018 (5)
C12	0.0436 (7)	0.0270 (6)	0.0281 (6)	−0.0043 (5)	0.0023 (5)	−0.0006 (5)
C13	0.0431 (7)	0.0280 (6)	0.0290 (6)	0.0053 (5)	0.0079 (5)	−0.0008 (5)
C14	0.0310 (6)	0.0320 (6)	0.0333 (7)	0.0041 (5)	0.0067 (5)	0.0014 (5)
N1A	0.0298 (12)	0.0274 (13)	0.033 (2)	0.0028 (12)	0.0048 (13)	−0.0035 (9)
O1A	0.0296 (12)	0.0240 (12)	0.0300 (19)	0.0007 (10)	0.0047 (14)	−0.0014 (7)
O1B	0.0296 (12)	0.0240 (12)	0.0300 (19)	0.0007 (10)	0.0047 (14)	−0.0014 (7)
N1B	0.0298 (12)	0.0274 (13)	0.033 (2)	0.0028 (12)	0.0048 (13)	−0.0035 (9)

Geometric parameters (Å, º)

C1—C1^i	1.331 (2)	C8—O1a	1.382 (4)
C1—C2	1.4656 (17)	C8—O1b	1.382 (4)
C1—H1	0.95	C9—O1b	1.377 (3)
C2—C3	1.3981 (17)	C9—C14	1.3845 (17)
C2—C7	1.3990 (17)	C9—C10	1.3878 (17)
C3—C4	1.3853 (17)	C9—N1a	1.405 (4)
C3—H3	0.95	C10—O1a	1.377 (3)
C4—C5	1.3917 (17)	C10—C11	1.3802 (17)
C4—H4	0.95	C10—N1b	1.405 (4)
C5—C6	1.3957 (17)	C11—C12	1.3855 (17)
C5—C8	1.4520 (17)	C11—H11	0.95
C6—C7	1.3760 (17)	C12—C13	1.3935 (18)
C6—H6	0.95	C12—H12	0.95
C7—H7	0.95	C13—C14	1.3862 (18)
C8—N1a	1.270 (5)	C13—H13	0.95
C8—N1b	1.270 (5)	C14—H14	0.95
C1^i—C1—C2	126.56 (15)	O1B—C9—C14	128.0 (2)
C1^i—C1—H1	116.7	O1B—C9—C10	111.0 (2)
C2—C1—H1	116.7	C14—C9—C10	121.04 (11)
C3—C2—C7	117.83 (11)	C14—C9—N1A	132.4 (2)
C3—C2—C1	118.91 (11)	C10—C9—N1A	106.5 (2)
C7—C2—C1	123.25 (11)	O1A—C10—C11	127.97 (17)
C4—C3—C2	121.65 (11)	O1A—C10—C9	109.03 (15)
C4—C3—H3	119.2	C11—C10—C9	122.99 (11)
C2—C3—H3	119.2	C11—C10—N1B	132.4 (3)
C3—C4—C5	119.63 (11)	C9—C10—N1B	104.6 (3)
C3—C4—H4	120.2	C10—C11—C12	115.86 (11)
C5—C4—H4	120.2	C10—C11—H11	122.1
C4—C5—C6	119.29 (11)	C12—C11—H11	122.1
C4—C5—C8	120.69 (11)	C11—C12—C13	121.67 (11)
C6—C5—C8	120.02 (11)	C11—C12—H12	119.2
C7—C6—C5	120.68 (11)	C13—C12—H12	119.2
C7—C6—H6	119.7	C14—C13—C12	121.90 (11)
C5—C6—H6	119.7	C14—C13—H13	119.1
C6—C7—C2	120.91 (11)	C12—C13—H13	119.1
C6—C7—H7	119.5	C9—C14—C13	116.53 (12)
C2—C7—H7	119.5	C9—C14—H14	121.7
N1A—C8—O1A	115.02 (12)	C13—C14—H14	121.7
N1B—C8—O1B	114.91 (13)	C8—N1A—C9	106.3 (3)
N1A—C8—C5	125.47 (19)	C10—O1A—C8	103.1 (2)
N1B—C8—C5	119.6 (2)	C9—O1B—C8	101.9 (3)
O1A—C8—C5	119.51 (16)	C8—N1B—C10	107.6 (4)
O1B—C8—C5	125.51 (17)

Symmetry code: (i) −x+3/2, −y−1/2, −z.

(I_375K) E)-4,4'-Bis(1,3-benzoxazol-2-yl)stilbene

Crystal data

C28H18N2O2	F(000) = 864
Mr = 414.44	Dx = 1.357 Mg m^−3
Monoclinic, C2/c	Cu Kα radiation, λ = 1.54178 Å
Hall symbol: -C 2yc	Cell parameters from 4605 reflections
a = 11.3459 (5) Å	θ = 3.0–68.5°
b = 6.0578 (3) Å	µ = 0.69 mm^−1
c = 29.6234 (15) Å	T = 375 K
β = 95.073 (3)°	Plate, yellow
V = 2028.08 (17) Å^3	0.60 × 0.18 × 0.05 mm
Z = 4

Data collection

Bruker SMART 6000 diffractometer	12519 independent reflections
Radiation source: rotating anode	9599 reflections with I > 2σ(I)
Montel 200 optics monochromator	Rint = 0.000
Detector resolution: 5.5 pixels mm^-1	θmax = 72.6°, θmin = 3.0°
ω scans	h = −13→13
Absorption correction: multi-scan (SADABS; Bruker, 2009)	k = −7→6
Tmin = 0.825, Tmax = 0.966	l = −36→36
13180 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.058	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.176	H-atom parameters constrained
S = 1.09	w = 1/[σ^2(Fo^2) + (0.0676P)^2 + 1.1894P] where P = (Fo^2 + 2Fc^2)/3
12519 reflections	(Δ/σ)max = 0.001
153 parameters	Δρmax = 0.19 e Å^−3
4 restraints	Δρmin = −0.16 e Å^−3

Special details

Experimental. X-ray crystallographic data for I were collected from a single-crystal sample, which was mounted on a loop fiber. Data were collected using a Bruker Platform diffractometer, equipped with a Bruker SMART 4 K Charged-Coupled Device (CCD) Area Detector using the program APEX2 and a Nonius FR591 rotating anode equiped with a Montel 200 optics The crystal-to-detector distance was 5.0 cm, and the data collection was carried out in 512 x 512 pixel mode. The initial unit-cell parameters were determined by a least-squares fit of the angular setting of strong reflections, collected by a 10.0 degree scan in 33 frames over three different parts of the reciprocal space (99 frames total). One complete sphere of data was collected, to better than 0.80Å resolution.

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
C1	0.70538 (11)	−0.21093 (19)	0.01000 (4)	0.0773 (3)
H1	0.6344	−0.2874	0.0049	0.093*
C2	0.70411 (10)	−0.01668 (17)	0.03946 (3)	0.0686 (3)
C3	0.59831 (10)	0.05354 (18)	0.05463 (4)	0.0764 (3)
H3	0.5296	−0.0250	0.0460	0.092*
C4	0.59146 (10)	0.23654 (18)	0.08223 (4)	0.0723 (3)
H4	0.5191	0.2794	0.0919	0.087*
C5	0.69340 (9)	0.35597 (16)	0.09541 (3)	0.0634 (3)
C6	0.79972 (10)	0.28613 (18)	0.08112 (4)	0.0753 (3)
H6	0.8686	0.3631	0.0903	0.090*
C7	0.80544 (11)	0.10393 (18)	0.05346 (4)	0.0774 (3)
H7	0.8780	0.0609	0.0440	0.093*
C8	0.68727 (10)	0.54776 (16)	0.12424 (3)	0.0660 (3)
C9	0.63072 (9)	0.81324 (16)	0.16504 (3)	0.0641 (3)
C10	0.75130 (9)	0.82895 (17)	0.16422 (3)	0.0643 (3)
C11	0.81765 (11)	0.99400 (19)	0.18614 (4)	0.0766 (3)
H11	0.8992	1.0034	0.1851	0.092*
C12	0.75515 (11)	1.14495 (19)	0.20983 (4)	0.0808 (3)
H12	0.7958	1.2587	0.2255	0.097*
C13	0.63459 (12)	1.13064 (19)	0.21072 (4)	0.0824 (3)
H13	0.5958	1.2352	0.2270	0.099*
C14	0.56925 (11)	0.96587 (19)	0.18821 (4)	0.0793 (3)
H14	0.4875	0.9582	0.1887	0.095*
N1A	0.5948 (3)	0.6287 (9)	0.1390 (2)	0.0723 (7)	0.712 (7)
O1A	0.7906 (2)	0.6577 (8)	0.1385 (2)	0.0678 (7)	0.712 (7)
O1B	0.5856 (4)	0.6386 (16)	0.1389 (5)	0.0678 (7)	0.288 (7)
N1B	0.7806 (6)	0.657 (3)	0.1357 (7)	0.0723 (7)	0.288 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0892 (8)	0.0673 (7)	0.0764 (8)	0.0020 (6)	0.0125 (6)	−0.0004 (5)
C2	0.0828 (8)	0.0617 (7)	0.0620 (6)	0.0025 (5)	0.0100 (5)	0.0018 (5)
C3	0.0778 (8)	0.0759 (8)	0.0760 (7)	−0.0055 (5)	0.0102 (6)	−0.0058 (5)
C4	0.0682 (7)	0.0753 (8)	0.0739 (7)	0.0038 (5)	0.0087 (5)	−0.0049 (5)
C5	0.0717 (7)	0.0579 (6)	0.0610 (6)	0.0030 (5)	0.0076 (5)	0.0046 (4)
C6	0.0700 (7)	0.0705 (7)	0.0864 (8)	0.0001 (5)	0.0116 (6)	−0.0064 (6)
C7	0.0744 (7)	0.0732 (8)	0.0864 (8)	0.0090 (5)	0.0170 (6)	−0.0022 (6)
C8	0.0761 (7)	0.0553 (6)	0.0666 (6)	0.0022 (5)	0.0053 (5)	0.0046 (5)
C9	0.0672 (6)	0.0610 (6)	0.0640 (6)	0.0023 (5)	0.0055 (5)	−0.0001 (5)
C10	0.0714 (7)	0.0584 (6)	0.0636 (6)	−0.0011 (5)	0.0092 (5)	0.0040 (4)
C11	0.0744 (7)	0.0739 (8)	0.0815 (8)	−0.0107 (5)	0.0060 (6)	−0.0013 (5)
C12	0.0987 (10)	0.0696 (8)	0.0743 (8)	−0.0085 (6)	0.0075 (6)	−0.0060 (5)
C13	0.1009 (10)	0.0723 (8)	0.0757 (8)	0.0089 (6)	0.0174 (7)	−0.0080 (6)
C14	0.0740 (7)	0.0792 (8)	0.0857 (8)	0.0083 (6)	0.0129 (6)	−0.0062 (6)
N1A	0.0675 (10)	0.0665 (13)	0.0823 (13)	0.0081 (10)	0.0035 (11)	−0.0093 (9)
O1A	0.0660 (10)	0.0618 (9)	0.0767 (15)	−0.0030 (8)	0.0119 (11)	−0.0013 (7)
O1B	0.0660 (10)	0.0618 (9)	0.0767 (15)	−0.0030 (8)	0.0119 (11)	−0.0013 (7)
N1B	0.0675 (10)	0.0665 (13)	0.0823 (13)	0.0081 (10)	0.0035 (11)	−0.0093 (9)

Geometric parameters (Å, º)

C1—C1^i	1.306 (2)	C8—O1b	1.381 (3)
C1—C2	1.4659 (14)	C8—O1a	1.382 (3)
C1—H1	0.93	C9—C10	1.3737 (14)
C2—C3	1.3854 (15)	C9—C14	1.3773 (14)
C2—C7	1.3940 (16)	C9—O1b	1.383 (2)
C3—C4	1.3837 (14)	C9—N1a	1.398 (3)
C3—H3	0.93	C10—C11	1.3791 (15)
C4—C5	1.3906 (15)	C10—O1a	1.383 (2)
C4—H4	0.93	C10—N1b	1.398 (3)
C5—C6	1.3796 (14)	C11—C12	1.3854 (16)
C5—C8	1.4474 (14)	C11—H11	0.93
C6—C7	1.3796 (14)	C12—C13	1.3732 (17)
C6—H6	0.93	C12—H12	0.93
C7—H7	0.93	C13—C14	1.3795 (15)
C8—N1a	1.270 (3)	C13—H13	0.93
C8—N1b	1.270 (4)	C14—H14	0.93
C1^i—C1—C2	127.57 (15)	O1A—C8—C5	118.94 (12)
C1^i—C1—H1	116.2	C10—C9—C14	120.75 (10)
C2—C1—H1	116.2	C10—C9—O1B	111.26 (17)
C3—C2—C7	117.26 (10)	C14—C9—O1B	127.92 (17)
C3—C2—C1	119.61 (11)	C10—C9—N1A	106.70 (15)
C7—C2—C1	123.13 (11)	C14—C9—N1A	132.54 (16)
C4—C3—C2	122.23 (11)	C9—C10—C11	123.01 (11)
C4—C3—H3	118.9	C9—C10—O1A	109.13 (12)
C2—C3—H3	118.9	C11—C10—O1A	127.86 (13)
C3—C4—C5	119.6 (1)	C9—C10—N1B	104.5 (2)
C3—C4—H4	120.2	C11—C10—N1B	132.4 (2)
C5—C4—H4	120.2	C10—C11—C12	115.76 (11)
C6—C5—C4	118.84 (10)	C10—C11—H11	122.1
C6—C5—C8	121.07 (10)	C12—C11—H11	122.1
C4—C5—C8	120.07 (10)	C13—C12—C11	121.56 (11)
C5—C6—C7	121.06 (11)	C13—C12—H12	119.2
C5—C6—H6	119.5	C11—C12—H12	119.2
C7—C6—H6	119.5	C12—C13—C14	122.00 (11)
C6—C7—C2	121.01 (11)	C12—C13—H13	119
C6—C7—H7	119.5	C14—C13—H13	119
C2—C7—H7	119.5	C9—C14—C13	116.90 (11)
N1A—C8—N1B	113.6 (3)	C9—C14—H14	121.6
N1B—C8—O1B	114.06 (17)	C13—C14—H14	121.6
N1A—C8—O1A	114.36 (10)	C8—N1A—C9	106.8 (2)
N1A—C8—C5	126.70 (15)	C8—O1A—C10	102.94 (16)
N1B—C8—C5	119.65 (18)	C8—O1B—C9	101.7 (2)
O1B—C8—C5	126.12 (14)	C8—N1B—C10	108.2 (3)

Symmetry code: (i) −x+3/2, −y−1/2, −z.