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The CuI-catalysed 1,3-dipolar cyclo­addition of an azide and a terminal alkyne is becoming an increasingly popular tool for synthetic chemists. This is the most representative of the so-called `click reactions' and it is used to generate 1,4-di­substituted triazoles in high yield. During studies on such cyclo­addition reactions, a reduced reactivity of an α-glucosyl azide with respect to the corresponding β-anomer was observed. With the aim of understanding this phenomenon, the structure of the title compound, C14H19N3O9, has been determined at 140 K. The glucopyranosyl ring appears in a regular 4C1 chair conformation with all the substituents in equatorial positions, except for the anomeric azide group, which adopts an axial orientation. The observed bond lengths are consistent with a strong anomeric effect, which is reflected in a change in dipolar character and hence reduced reactivity of the α-glucosyl azide.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270108020702/bm3053sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270108020702/bm3053Isup2.hkl
Contains datablock I

CCDC reference: 700033

Comment top

Glycosyl azides represent important and versatile building blocks in carbohydrate chemistry (Györgydeák & Thiem, 2006). They have been widely used as synthetic intermediates for the preparation of glycosyl amines, asparagine-linked glycopeptides (Herzner et al., 2000) and, more recently, triazole-linked neoglycoconjugates (Dedola et al., 2007; Dondoni, 2007). These last became available as a result of the discovery of the highly efficient CuI-catalysed cycloaddition reaction between azides and terminal alkynes (Rostovtsev et al., 2002; Tornøe et al., 2002), which is commonly referred to as `click chemistry'. This cycloaddition process has been extensively used for the synthesis of a variety of neoglycoconjugates (Dedola et al., 2007; Dondoni, 2007). In the course of our work on the synthesis of starch-like molecules, we experienced major problems with stereocontrol in the synthesis of inter-sugar chain glycosidic linkages (Marmuse et al., 2005a). We therefore resorted to the preparation of pseudo-starch fragments based on glucosyl triazole linkages (Marmuse et al., 2005b; Nepogodiev et al., 2007). Initial studies were based on the immediately accessible β-linked sugar azides, which do not mirror the anomeric stereochemistry of starch. Here, we report the structural analysis of the title compound, (I) (Bianchi & Bernardi, 2006). The X-ray structure of the corresponding β-linked anomer, 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl azide, (II), has already been reported (Temelkoff et al., 2004). Crystals of (I) suitable for X-ray crystallographic analysis were obtained by recrystallization from methanol [Ethanol in prep - which is correct?].

The six-membered pyranose ring in (I) adopts a chair conformation, with all exocyclic substituents adopting an equatorial arrangement, except the anomeric azide which has the expected axial orientation (Fig. 1). Compared with the structure of the corresponding β-anomer, (II) (Temelkoff et al., 2004), the geometry of the pyranose ring and the orientation of the acetate groups of (I) are very similar. However, whereas the length of the C1—O5 bond in (I) [1.423 (3) Å] is the same as in (II) [1.420 (2) Å], the C1—N11 [1.510 (3) versus 1.460 (2) Å] and C5—O5 [1.459 (3) versus 1.432 (2) Å] distances in (I) are significantly longer than in (II). As in the β-anomer, (II), the azido group in (I) appears as a nearly linear fragment [N11—N12—N13 = 173.0 (3)°, compared with 171.4 (2)° for the β-anomer] and shows a very similar C1—N11—N12 bond angle [113.7 (2) versus 113.74 (14)° for the β-anomer].

However, the N—N bond lengths for the azide group and C1—N11 distances in (I) and (II) are different. The structural differences between the anomeric glucosyl azides are all in keeping with the expected influence of the anomeric effect (Briggs et al., 1984; Wolfe et al., 1979). For the β-azide, (II), the terminal N12—N13 bond [1.119 (3) Å] is shorter than the N11—N12 bond [1.243 (2) Å], whereas in the α-azide, (I), these are similar [1.195 (4) and 1.165 (3) Å, respectively]. One might therefore anticipate a significant reactivity difference between compounds (I) and (II) in dipolar cycloaddition chemistry, which we have indeed observed: a much lower reactivity of α-azide (I) compared with β-azide (II) is evident in the CuI-catalysed synthesis of triazoles. This is consistent with other experimental observations (Wilkinson et al., 2006) and in accord with computational studies, which show the crucial role that a partial negative charge on atom N11 plays in the mechanism of the CuI-catalysed cycloaddition of azides and alkynes (Himo et al., 2005).

Experimental top

2,3,4,6-Tetra-O-acetyl-α-D-glucopyranosyl azide, (I), was prepared along with the β-anomer, (II), in a 9:1 ratio (determined by 1H NMR spectroscopy), as described previously (Bianchi & Bernardi, 2006), using tetra-O-acetyl-β-D-glucopyranosyl chloride (Korytnyk & Mills, 1959) and Me3SiN3 (Soli et al., 1999). Single isomers were obtained using purification by silica-gel column chromatography. Crystals of (I) suitable for X-ray diffraction analysis were obtained as colourless blocks by recrystallization from ethanol [Methanol in comment - which is correct?].

Refinement top

Non-H atoms were refined with anisotropic displacement parameters, except those in the CH2OCOMe group of C6 where there is suspected disorder; the major [79.9 (5)%] component C6/O6/C61/O61/C62 was refined anisotropically, but the minor [20.1 (5)%] component C7/O7/C71/O71/C72 was not fully resolved and its C and O atoms were refined isotropically; the methyl C atom represented by C62/C72 was found to be common to both orientations and was refined with full occupancy for that site, using the EXYZ and EADP restraints in SHELXL97 (Sheldrick, 2008).

H atoms were included in idealized positions, with C—H distances for the methyl, methylene and methine groups set to 0.96, 0.97 and 0.98 Å, respectively, and with Uiso(H) = 1.5Ueq(C) for the methyl group and 1.2Ueq(C) for the remaining groups.

The absolute configuration of the C atoms cannot be determined from the X-ray data; its assignment was based on the known configuration of the starting material.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2007); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED (Oxford Diffraction, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and publCIF (Westrip, 2008).

Figures top
[Figure 1] Fig. 1. A view of the molecular structure of (I), showing the atom-numbering scheme. For clarity, only the major component of the disordered CH2OCOMe group at C6 is shown. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as capped sticks.
2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl azide top
Crystal data top
C14H19N3O9F(000) = 392
Mr = 373.32Dx = 1.387 Mg m3
Monoclinic, P21Mo Kα radiation, λ = 0.71073 Å
a = 10.806 (4) ÅCell parameters from 474 reflections
b = 7.9840 (13) Åθ = 3.9–25°
c = 11.0107 (8) ŵ = 0.12 mm1
β = 109.742 (2)°T = 140 K
V = 894.1 (3) Å3Block, colourless
Z = 20.45 × 0.43 × 0.30 mm
Data collection top
Oxford Diffraction Xcalibur3/CCD
diffractometer
3125 independent reflections
Radiation source: Enhance (Mo) X-ray Source2216 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.039
Detector resolution: 16.0050 pixels mm-1θmax = 25.0°, θmin = 3.9°
Thin–slice ϕ and ω scansh = 1212
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2006)
k = 99
Tmin = 0.940, Tmax = 1.060l = 1313
8905 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.039H-atom parameters constrained
wR(F2) = 0.087 w = 1/[σ2(Fo2) + (0.0523P)2]
where P = (Fo2 + 2Fc2)/3
S = 0.90(Δ/σ)max = 0.007
3125 reflectionsΔρmax = 0.15 e Å3
257 parametersΔρmin = 0.16 e Å3
1 restraintAbsolute structure: Flack (1983), with how many Friedel pairs?
Primary atom site location: structure-invariant direct methodsAbsolute structure parameter: 0.6 (12)
Crystal data top
C14H19N3O9V = 894.1 (3) Å3
Mr = 373.32Z = 2
Monoclinic, P21Mo Kα radiation
a = 10.806 (4) ŵ = 0.12 mm1
b = 7.9840 (13) ÅT = 140 K
c = 11.0107 (8) Å0.45 × 0.43 × 0.30 mm
β = 109.742 (2)°
Data collection top
Oxford Diffraction Xcalibur3/CCD
diffractometer
3125 independent reflections
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2006)
2216 reflections with I > 2σ(I)
Tmin = 0.940, Tmax = 1.060Rint = 0.039
8905 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.039H-atom parameters constrained
wR(F2) = 0.087Δρmax = 0.15 e Å3
S = 0.90Δρmin = 0.16 e Å3
3125 reflectionsAbsolute structure: Flack (1983), with how many Friedel pairs?
257 parametersAbsolute structure parameter: 0.6 (12)
1 restraint
Special details top

Experimental. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
C10.4935 (2)0.4785 (3)0.8762 (3)0.0365 (7)
H10.52580.42750.96220.044*
N110.60522 (19)0.5749 (3)0.8561 (2)0.0316 (5)
N120.6708 (2)0.6454 (3)0.9479 (3)0.0450 (6)
N130.7454 (3)0.7240 (4)1.0341 (3)0.0659 (8)
C20.4493 (2)0.3376 (3)0.7762 (3)0.0346 (7)
H20.39420.25950.80410.041*
O20.56490 (15)0.2480 (2)0.77214 (17)0.0392 (4)
C210.5704 (3)0.0787 (3)0.7919 (2)0.0360 (6)
O210.4879 (2)0.0022 (2)0.8188 (2)0.0533 (5)
C220.6916 (3)0.0095 (4)0.7734 (3)0.0522 (8)
H22A0.68730.11060.77170.078*
H22B0.76760.04500.84340.078*
H22C0.69740.04970.69340.078*
C30.3714 (2)0.3984 (3)0.6407 (3)0.0327 (6)
H30.42930.45350.60120.039*
O30.30652 (14)0.2529 (2)0.56419 (16)0.0338 (4)
C310.3639 (2)0.1759 (3)0.4855 (2)0.0342 (6)
O310.46248 (16)0.2268 (3)0.46931 (18)0.0490 (5)
C320.2893 (2)0.0208 (3)0.4269 (3)0.0412 (7)
H32A0.32320.07280.48310.062*
H32B0.29920.00010.34480.062*
H32C0.19790.03570.41530.062*
C40.2630 (2)0.5170 (3)0.6461 (2)0.0345 (6)
H40.19750.45530.67190.041*
O40.20107 (15)0.5914 (2)0.51965 (17)0.0390 (5)
C410.0706 (3)0.5590 (3)0.4578 (3)0.0416 (7)
O410.0051 (2)0.4730 (3)0.5040 (2)0.0624 (6)
C420.0191 (3)0.6445 (4)0.3296 (3)0.0522 (8)
H42A0.07340.66460.30810.078*
H42B0.03370.57460.26480.078*
H42C0.06390.74930.33360.078*
C50.3220 (2)0.6586 (3)0.7430 (2)0.0393 (7)
H50.38910.71590.71680.047*
O50.38603 (16)0.5849 (2)0.87015 (17)0.0418 (5)
C60.2211 (3)0.7870 (5)0.7490 (5)0.0398 (11)0.799 (5)
H6A0.26120.86820.81640.048*0.799 (5)
H6B0.18690.84590.66740.048*0.799 (5)
O60.1157 (2)0.6995 (3)0.7761 (3)0.0445 (8)0.799 (5)
C610.1025 (4)0.7172 (6)0.8924 (4)0.0472 (10)0.799 (5)
O610.1712 (3)0.8089 (4)0.9752 (3)0.0785 (11)0.799 (5)
C620.0065 (3)0.5920 (7)0.9073 (4)0.0917 (15)0.799 (5)
H62A0.02630.62020.98350.138*0.799 (5)
H62B0.02590.47920.91420.138*0.799 (5)
H62C0.08480.60130.83310.138*0.799 (5)
C70.212 (2)0.746 (2)0.7968 (18)0.038 (5)*0.201 (5)
H7A0.25570.82330.86610.046*0.201 (5)
H7B0.14970.80950.72780.046*0.201 (5)
O70.1410 (9)0.6185 (14)0.8444 (10)0.037 (3)*0.201 (5)
C710.020 (2)0.653 (3)0.856 (2)0.057 (6)*0.201 (5)
O710.0305 (15)0.793 (2)0.8063 (16)0.111 (6)*0.201 (5)
C720.0065 (3)0.5920 (7)0.9073 (4)0.0917 (15)0.201 (5)
H72A0.10080.59420.87970.138*0.201 (5)
H72B0.02890.63480.99370.138*0.201 (5)
H72C0.02290.47890.90530.138*0.201 (5)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0354 (14)0.0290 (15)0.0456 (17)0.0025 (13)0.0145 (13)0.0054 (13)
N110.0273 (11)0.0258 (11)0.0417 (14)0.0030 (10)0.0117 (10)0.0006 (11)
N120.0411 (14)0.0472 (15)0.0514 (16)0.0132 (13)0.0218 (13)0.0147 (14)
N130.0573 (16)0.079 (2)0.0597 (18)0.0045 (16)0.0172 (14)0.0126 (18)
C20.0320 (14)0.0252 (14)0.0511 (19)0.0006 (12)0.0200 (14)0.0003 (13)
O20.0339 (9)0.0233 (10)0.0623 (12)0.0041 (8)0.0188 (8)0.0064 (9)
C210.0505 (16)0.0229 (14)0.0330 (15)0.0022 (14)0.0120 (13)0.0009 (12)
O210.0709 (14)0.0283 (10)0.0710 (14)0.0057 (10)0.0373 (12)0.0012 (10)
C220.0528 (17)0.0314 (16)0.069 (2)0.0097 (14)0.0164 (16)0.0013 (16)
C30.0293 (13)0.0267 (14)0.0442 (16)0.0024 (12)0.0151 (12)0.0009 (12)
O30.0323 (9)0.0259 (10)0.0468 (11)0.0047 (8)0.0182 (8)0.0061 (9)
C310.0329 (14)0.0278 (14)0.0424 (16)0.0069 (13)0.0137 (12)0.0004 (13)
O310.0463 (11)0.0441 (12)0.0677 (14)0.0058 (10)0.0336 (10)0.0126 (10)
C320.0415 (15)0.0352 (16)0.0476 (17)0.0022 (13)0.0160 (13)0.0073 (14)
C40.0298 (13)0.0262 (14)0.0465 (16)0.0018 (12)0.0117 (12)0.0030 (13)
O40.0295 (9)0.0314 (10)0.0525 (12)0.0004 (8)0.0092 (8)0.0023 (9)
C410.0317 (16)0.0282 (16)0.0619 (19)0.0046 (13)0.0120 (14)0.0100 (14)
O410.0361 (10)0.0660 (15)0.0792 (15)0.0098 (11)0.0118 (10)0.0055 (13)
C420.0436 (16)0.0457 (18)0.0595 (19)0.0044 (14)0.0072 (14)0.0100 (16)
C50.0308 (13)0.0336 (15)0.0493 (18)0.0032 (13)0.0079 (13)0.0047 (14)
O50.0415 (10)0.0376 (10)0.0496 (12)0.0028 (9)0.0197 (9)0.0038 (10)
C60.038 (2)0.040 (3)0.041 (3)0.0038 (18)0.013 (2)0.002 (2)
O60.0362 (14)0.0508 (19)0.0487 (18)0.0012 (13)0.0172 (12)0.0135 (15)
C610.050 (2)0.050 (3)0.042 (2)0.001 (2)0.016 (2)0.006 (2)
O610.098 (2)0.083 (2)0.061 (2)0.0313 (19)0.0354 (18)0.0252 (18)
C620.064 (2)0.147 (5)0.064 (3)0.018 (3)0.021 (2)0.009 (3)
C720.064 (2)0.147 (5)0.064 (3)0.018 (3)0.021 (2)0.009 (3)
Geometric parameters (Å, º) top
C1—O51.423 (3)C4—H40.9800
C1—N111.510 (3)O4—C411.367 (3)
C1—C21.533 (4)C41—O411.214 (4)
C1—H10.9800C41—C421.496 (4)
N11—N121.165 (3)C42—H42A0.9600
N12—N131.195 (4)C42—H42B0.9600
C2—O21.453 (3)C42—H42C0.9600
C2—C31.523 (4)C5—O51.459 (3)
C2—H20.9800C5—C61.514 (4)
O2—C211.367 (3)C5—C71.652 (18)
C21—O211.198 (3)C5—H50.9800
C21—C221.497 (4)C6—O61.450 (5)
C22—H22A0.9600C6—H6A0.9700
C22—H22B0.9600C6—H6B0.9700
C22—H22C0.9600O6—C611.343 (5)
C3—O31.467 (3)C61—O611.209 (5)
C3—C41.522 (3)C61—C621.595 (7)
C3—H30.9800C62—H62A0.9600
O3—C311.369 (3)C62—H62B0.9600
C31—O311.209 (3)C62—H62C0.9600
C31—C321.499 (4)C7—O71.47 (2)
C32—H32A0.9600C7—H7A0.9700
C32—H32B0.9600C7—H7B0.9700
C32—H32C0.9600O7—C711.39 (2)
C4—O41.453 (3)C71—O711.28 (2)
C4—C51.538 (3)
O5—C1—N11111.7 (2)O4—C4—C3109.2 (2)
O5—C1—C2110.69 (19)O4—C4—C5108.27 (19)
N11—C1—C2109.9 (2)C3—C4—C5109.90 (18)
O5—C1—H1108.2O4—C4—H4109.8
N11—C1—H1108.2C3—C4—H4109.8
C2—C1—H1108.2C5—C4—H4109.8
N12—N11—C1113.7 (2)C41—O4—C4117.6 (2)
N11—N12—N13173.0 (3)O41—C41—O4123.2 (3)
O2—C2—C3108.9 (2)O41—C41—C42124.7 (2)
O2—C2—C1108.71 (18)O4—C41—C42112.1 (2)
C3—C2—C1113.9 (2)C41—C42—H42A109.5
O2—C2—H2108.4C41—C42—H42B109.5
C3—C2—H2108.4H42A—C42—H42B109.5
C1—C2—H2108.4C41—C42—H42C109.5
C21—O2—C2118.3 (2)H42A—C42—H42C109.5
O21—C21—O2123.2 (2)H42B—C42—H42C109.5
O21—C21—C22127.1 (2)O5—C5—C6110.3 (2)
O2—C21—C22109.7 (2)O5—C5—C4108.7 (2)
C21—C22—H22A109.5C6—C5—C4113.1 (2)
C21—C22—H22B109.5C4—C5—C7112.3 (8)
H22A—C22—H22B109.5O5—C5—H5108.2
C21—C22—H22C109.5C6—C5—H5108.2
H22A—C22—H22C109.5C4—C5—H5108.2
H22B—C22—H22C109.5C1—O5—C5113.63 (18)
O3—C3—C4106.88 (18)O6—C6—C5108.1 (3)
O3—C3—C2108.0 (2)O6—C6—H6A110.1
C4—C3—C2109.8 (2)C5—C6—H6A110.1
O3—C3—H3110.7O6—C6—H6B110.1
C4—C3—H3110.7C5—C6—H6B110.1
C2—C3—H3110.7H6A—C6—H6B108.4
C31—O3—C3119.25 (17)C61—O6—C6119.3 (3)
O31—C31—O3123.5 (2)O61—C61—O6123.2 (4)
O31—C31—C32125.9 (2)O61—C61—C62126.1 (3)
O3—C31—C32110.5 (2)O6—C61—C62110.6 (4)
C31—C32—H32A109.5O7—C7—C5111.1 (12)
C31—C32—H32B109.5O7—C7—H7A109.4
H32A—C32—H32B109.5C5—C7—H7A109.4
C31—C32—H32C109.5O7—C7—H7B109.4
H32A—C32—H32C109.5C5—C7—H7B109.4
H32B—C32—H32C109.5H7A—C7—H7B108.0
O5—C1—N11—N1280.0 (3)C4—O4—C41—O410.6 (4)
C2—C1—N11—N12156.8 (2)C4—O4—C41—C42179.4 (2)
O5—C1—C2—O2171.38 (19)O4—C4—C5—O5179.26 (17)
N11—C1—C2—O247.6 (3)C3—C4—C5—O560.1 (2)
O5—C1—C2—C349.8 (3)O4—C4—C5—C658.0 (3)
N11—C1—C2—C373.9 (2)C3—C4—C5—C6177.1 (3)
C3—C2—O2—C21110.9 (2)O4—C4—C5—C783.3 (7)
C1—C2—O2—C21124.6 (2)C3—C4—C5—C7157.6 (7)
C2—O2—C21—O214.0 (4)N11—C1—O5—C565.7 (3)
C2—O2—C21—C22175.6 (2)C2—C1—O5—C557.0 (3)
O2—C2—C3—O373.3 (2)C6—C5—O5—C1172.6 (2)
C1—C2—C3—O3165.26 (18)C4—C5—O5—C162.9 (2)
O2—C2—C3—C4170.52 (19)C7—C5—O5—C1176.4 (8)
C1—C2—C3—C449.1 (3)O5—C5—C6—O667.0 (3)
C4—C3—O3—C31144.5 (2)C4—C5—C6—O654.9 (4)
C2—C3—O3—C3197.4 (2)C7—C5—C6—O638 (2)
C3—O3—C31—O314.4 (3)C5—C6—O6—C61109.1 (4)
C3—O3—C31—C32174.2 (2)C6—O6—C61—O613.2 (6)
O3—C3—C4—O470.7 (2)C6—O6—C61—C62172.4 (3)
C2—C3—C4—O4172.40 (19)O5—C5—C7—O758.9 (12)
O3—C3—C4—C5170.7 (2)C6—C5—C7—O7148 (3)
C2—C3—C4—C553.8 (3)C4—C5—C7—O751.2 (13)
C3—C4—O4—C41117.6 (2)C5—C7—O7—C71159.7 (14)
C5—C4—O4—C41122.8 (2)C7—O7—C71—O719 (3)

Experimental details

Crystal data
Chemical formulaC14H19N3O9
Mr373.32
Crystal system, space groupMonoclinic, P21
Temperature (K)140
a, b, c (Å)10.806 (4), 7.9840 (13), 11.0107 (8)
β (°) 109.742 (2)
V3)894.1 (3)
Z2
Radiation typeMo Kα
µ (mm1)0.12
Crystal size (mm)0.45 × 0.43 × 0.30
Data collection
DiffractometerOxford Diffraction Xcalibur3/CCD
diffractometer
Absorption correctionMulti-scan
(CrysAlis RED; Oxford Diffraction, 2006)
Tmin, Tmax0.940, 1.060
No. of measured, independent and
observed [I > 2σ(I)] reflections
8905, 3125, 2216
Rint0.039
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.039, 0.087, 0.90
No. of reflections3125
No. of parameters257
No. of restraints1
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.15, 0.16
Absolute structureFlack (1983), with how many Friedel pairs?
Absolute structure parameter0.6 (12)

Computer programs: CrysAlis CCD (Oxford Diffraction, 2007), CrysAlis RED (Oxford Diffraction, 2006), SHELXS97 (Sheldrick, 2008), Mercury (Macrae et al., 2006), SHELXL97 (Sheldrick, 2008) and publCIF (Westrip, 2008).

 

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