Stable polymorph of morphine

Gelbrich, T.; Braun, D.E.; Griesser, U.J.

doi:10.1107/S1600536812048945

organic compounds

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Volume 69| Part 1| January 2013| Page o2

https://doi.org/10.1107/S1600536812048945

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Stable polymorph of morphine¹

Thomas Gelbrich,^a ^* Doris E. Braun ^a and Ulrich J. Griesser ^a

^aInstitute of Pharmacy, University of Innsbruck, Innrain 52c, 6020 Innsbruck, Austria
^*Correspondence e-mail: thomas.gelbrich@uibk.ac.at

(Received 19 November 2012; accepted 28 November 2012; online 5 December 2012)

In the stable polymorph of the title compound, C₁₇H₁₉NO₃ [systematic name: (5α,6α)-7,8-didehydro-4,5-epoxy-17-methylmorphinan-3,6-diol], the molecular conformation is in agreement with the characteristics of previously reported morphine forms. The molecule displays the typical T-shape and its piperidine ring adopts a slightly distorted chair conformation. Intermolecular O—H⋯O hydrogen bonds link the molecules into helical chains parallel to the b axis. Intramolecular O—H⋯O hydrogen bonds are also observed.

Related literature

For related structures, see: Guguta et al. (2008 ); Gylbert (1973 ); Mackay & Hodgkin (1955 ); Bye (1976 ); Wongweichintana et al. (1984 ); Lutz & Spek (1998 ); Scheins et al. (2005 ); Gelbrich et al. (2012 ). For decriptions of morphine polymorphs, see: Kofler (1933 ); Kuhnert-Brandstätter et al. (1975 ). For a description of the Cambridge Structural Database, see: Allen (2002 ). For the program XPac, see: Gelbrich & Hursthouse (2005 ).

Experimental

Crystal data

C₁₇H₁₉NO₃
M_r = 285.33
Orthorhombic, P 2₁ 2₁ 2₁
a = 7.6989 (10) Å
b = 12.737 (4) Å
c = 13.740 (4) Å
V = 1347.4 (6) Å³
Z = 4
Cu Kα radiation
μ = 0.78 mm⁻¹
T = 173 K
0.15 × 0.10 × 0.03 mm

Data collection

Oxford Diffraction Xcalibur (Ruby, Gemini ultra) diffractometer
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2003 $[Oxford Diffraction (2003). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd., Abingdon, Oxfordshire, England.]$ ) T_min = 0.624, T_max = 1.000
13009 measured reflections
1408 independent reflections
977 reflections with I > 2σ(I)
R_int = 0.118

Refinement

R[F² > 2σ(F²)] = 0.068
wR(F²) = 0.141
S = 1.01
1408 reflections
192 parameters
H-atom parameters constrained
Δρ_max = 0.27 e Å⁻³
Δρ_min = −0.26 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯O3ⁱ	0.84	1.96	2.757 (6)	159
O3—H3⋯O2	0.84	2.17	2.629 (6)	114
Symmetry code: (i) $[-x, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ .

Data collection: CrysAlis PRO (Oxford Diffraction, 2003 $[Oxford Diffraction (2003). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd., Abingdon, Oxfordshire, England.]$ ); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Bruker, 1998 ) and Mercury (Bruno et al., 2002 ); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536812048945/im2413sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536812048945/im2413Isup2.hkl

checkCIF report

Comment top

Morphine is the main alkaloid of opium, the dried latex of the opium poppy (Papaver somniferum). The Cambridge Structural Database (CSD; version 5.33 and updates; Allen, 2002) contains a number of free base and salt structures of morphine: a monohydrate (Bye, 1976), a hydrochloride trihydrate (Gylbert, 1973), a hydroiodide dihydrate (Mackay & Hodgkin, 1955), a complex with β-phenylhydracrylic acid (Lutz & Spek, 1998) and a bis(morphinium) dihydrogensulfate pentahydrate (Wongweichintana et al., 1984). A hydrochloride anhydrate structure was recently reported by us (Gelbrich et al., 2012). The title structure was previously solved from powder data by Guguta et al. (2008), however the corresponding atomic coordinates are not available from the CSD or from supplementary materials accompanying this report.

According to Kofler (1933), morphine can exist in two distinct polymorphic modifications, and the characteristics of the crystals investigated by us match Kofler's description of the stable form. Our thermomicroscopy experiments have shown that the investigated crystals melt under decomposition at 254 °C (the applied heating rate was 5 °C per minute). This behaviour is in agreement with reports given by Kofler (1933) and Kuhnert-Brandstätter et al. (1975).

The geometry of the molecular morphine scaffold (Figure 1) with its five rings agrees with the characteristics of the related salt and free base structures mentioned above. The title structure displays two sets of O—H···O bonds, one of which is intramolecular and the other is intermolecular (Table 1). Intermolecular hydrogen bonds link the morphine molecules into an infinite helical chain that propagates parallel to the b-axis (Figure 2).

The packing of the geometrically inflexible morphine moieties in the title structure was compared with corresponding packing arrangements present in the six morphine forms mentioned above (Bye, 1976; Gelbrich et al., 2012; Gylbert, 1973; Mackay & Hodgkin, 1955; Lutz & Spek, 1998; Wongweichintana et al., 1984), using the program XPac (Gelbrich & Hursthouse, 2005). These comparisons have shown that the packing mode of morphine molecules in the stable form is unique and has no supramolecular constructs in common with any of the other structures in this group.

Related literature top

For related structures, see: Guguta et al. (2008); Gylbert (1973); Mackay & Hodgkin (1955); Bye (1976); Wongweichintana et al. (1984); Lutz & Spek (1998); Scheins et al. (2005); Gelbrich et al. (2012). For decriptions of morphine polymorphs, see: Kofler (1933); Kuhnert-Brandstätter et al. (1975). For a description of the Cambridge Structural Database, see: Allen (2002). For the program XPac, see: Gelbrich & Hursthouse (2005).

Experimental top

Morphine was obtained from Heilmittelwerke Wien, Austria. Very thin, plate-shaped crystals of the stable polymorph were yielded from a sublimation experiment carried out on a Kofler hot bench at approximately 150 °C, using two glass slides separated by a spacer ring of 1 cm height.

Structure description top

For related structures, see: Guguta et al. (2008); Gylbert (1973); Mackay & Hodgkin (1955); Bye (1976); Wongweichintana et al. (1984); Lutz & Spek (1998); Scheins et al. (2005); Gelbrich et al. (2012). For decriptions of morphine polymorphs, see: Kofler (1933); Kuhnert-Brandstätter et al. (1975). For a description of the Cambridge Structural Database, see: Allen (2002). For the program XPac, see: Gelbrich & Hursthouse (2005).

Computing details top

Data collection: CrysAlis PRO (Oxford Diffraction, 2003); cell refinement: CrysAlis PRO (Oxford Diffraction, 2003); data reduction: CrysAlis PRO (Oxford Diffraction, 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Bruker, 1998) and Mercury (Bruno et al., 2002); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

	Fig. 1. Molcular structure of morphine with displacement ellipsoids are drawn at the 50% probability level and hydrogen atoms shown as spheres of arbitrary size.
	Fig. 2. Hydrogen bonded helical chain. Intramolecular and intermolecular O—H···O bonds are drawn as broken lines; H and O atoms involved in hydrogen bonding are drawn as balls [symmetry code: (i) -x, y + 1/2, -z + 3/2.].

(5α,6α)-7,8-Didehydro-4,5-epoxy-17-methylmorphinan-3,6-diol top

Crystal data top

C₁₇H₁₉NO₃	F(000) = 608
M_r = 285.33	D_x = 1.407 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Cu Kα radiation, λ = 1.54180 Å
Hall symbol: P 2ac 2ab	Cell parameters from 1360 reflections
a = 7.6989 (10) Å	θ = 3.2–68.2°
b = 12.737 (4) Å	µ = 0.78 mm⁻¹
c = 13.740 (4) Å	T = 173 K
V = 1347.4 (6) Å³	Plate, colourless
Z = 4	0.15 × 0.10 × 0.03 mm

Data collection top

Oxford Diffraction Xcalibur (Ruby, Gemini ultra) diffractometer	1408 independent reflections
Radiation source: Enhance (Mo) X-ray Source	977 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.118
Detector resolution: 10.3575 pixels mm^-1	θ_max = 68.2°, θ_min = 4.7°
ω scans	h = −9→8
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2003)	k = −14→15
T_min = 0.624, T_max = 1.000	l = −16→16
13009 measured reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.068	H-atom parameters constrained
wR(F²) = 0.141	w = 1/[σ²(F_o²) + (0.0112P)² + 2.P] where P = (F_o² + 2F_c²)/3
S = 1.01	(Δ/σ)_max < 0.001
1408 reflections	Δρ_max = 0.27 e Å⁻³
192 parameters	Δρ_min = −0.26 e Å⁻³
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0043 (4)

Crystal data top

C₁₇H₁₉NO₃	V = 1347.4 (6) Å³
M_r = 285.33	Z = 4
Orthorhombic, P2₁2₁2₁	Cu Kα radiation
a = 7.6989 (10) Å	µ = 0.78 mm⁻¹
b = 12.737 (4) Å	T = 173 K
c = 13.740 (4) Å	0.15 × 0.10 × 0.03 mm

Data collection top

Oxford Diffraction Xcalibur (Ruby, Gemini ultra) diffractometer	1408 independent reflections
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2003)	977 reflections with I > 2σ(I)
T_min = 0.624, T_max = 1.000	R_int = 0.118
13009 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.068	0 restraints
wR(F²) = 0.141	H-atom parameters constrained
S = 1.01	Δρ_max = 0.27 e Å⁻³
1408 reflections	Δρ_min = −0.26 e Å⁻³
192 parameters

Special details top

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.

The Flack x parameter (Flack, 1983) and the Hooft y parameter (Hooft et al., 2008) were both indeterminate due to a lack of significant resonant scattering. Accordingly, Friedel opposites were merged prior to the final refinement. [Flack, H. D. (1983). Acta Cryst. A39, 876–881; Hooft, R. W. W., Straver, L. H. & Spek, A. L. (2008). J. Appl. Cryst. 41, 96–103.]

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

	x	y	z	U_iso*/U_eq
O1	0.0998 (5)	0.6564 (3)	0.7856 (3)	0.0520 (12)
H1	0.0431	0.7103	0.7705	0.062*
O2	0.3165 (5)	0.4742 (3)	0.7958 (3)	0.0466 (11)
O3	0.1429 (6)	0.2969 (3)	0.7838 (3)	0.0546 (12)
H3	0.1096	0.3587	0.7941	0.066*
N1	0.8422 (6)	0.4378 (4)	0.5555 (4)	0.0492 (14)
C1	0.3549 (8)	0.6662 (5)	0.5563 (5)	0.0458 (15)
H1A	0.3611	0.7068	0.4984	0.055*
C2	0.2382 (8)	0.6935 (5)	0.6290 (5)	0.0466 (16)
H2	0.1665	0.7534	0.6198	0.056*
C3	0.2223 (7)	0.6362 (5)	0.7147 (5)	0.0429 (15)
C4	0.3281 (7)	0.5499 (4)	0.7238 (5)	0.0408 (14)
C5	0.2959 (8)	0.2985 (5)	0.7233 (5)	0.0494 (17)
H5	0.3554	0.2293	0.7320	0.059*
C6	0.4208 (7)	0.3836 (5)	0.7615 (5)	0.0462 (16)
H6	0.4902	0.3548	0.8168	0.055*
C7	0.2554 (9)	0.3091 (5)	0.6180 (5)	0.0499 (17)
H7	0.1398	0.2980	0.5961	0.060*
C8	0.3781 (9)	0.3338 (5)	0.5537 (5)	0.0506 (17)
H8	0.3524	0.3340	0.4861	0.061*
C9	0.6652 (8)	0.4267 (5)	0.5160 (5)	0.0450 (15)
H9	0.6748	0.3841	0.4551	0.054*
C10	0.5732 (8)	0.5321 (5)	0.4878 (5)	0.0491 (17)
H10A	0.6630	0.5838	0.4686	0.059*
H10B	0.4984	0.5194	0.4304	0.059*
C11	0.4634 (7)	0.5792 (5)	0.5682 (4)	0.0410 (14)
C12	0.4530 (7)	0.5257 (5)	0.6546 (4)	0.0386 (14)
C13	0.5465 (8)	0.4258 (5)	0.6810 (4)	0.0415 (15)
C14	0.5584 (8)	0.3617 (5)	0.5888 (5)	0.0466 (16)
H14	0.6227	0.2953	0.6033	0.056*
C15	0.7290 (7)	0.4477 (5)	0.7212 (5)	0.0443 (15)
H15A	0.7199	0.4948	0.7783	0.053*
H15B	0.7818	0.3809	0.7432	0.053*
C16	0.8453 (8)	0.4978 (5)	0.6457 (5)	0.0521 (17)
H16A	0.8056	0.5704	0.6329	0.062*
H16B	0.9657	0.5012	0.6708	0.062*
C17	0.9652 (8)	0.4788 (6)	0.4841 (5)	0.060 (2)
H17A	0.9335	0.5510	0.4672	0.090*
H17B	0.9621	0.4350	0.4254	0.090*
H17C	1.0826	0.4778	0.5117	0.090*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.040 (2)	0.053 (2)	0.063 (3)	0.012 (2)	0.008 (2)	0.002 (2)
O2	0.031 (2)	0.048 (2)	0.060 (3)	0.0019 (19)	0.004 (2)	0.000 (2)
O3	0.040 (2)	0.050 (2)	0.074 (3)	−0.006 (2)	0.014 (3)	−0.002 (2)
N1	0.026 (2)	0.063 (3)	0.059 (3)	0.001 (3)	0.005 (2)	0.003 (3)
C1	0.040 (3)	0.043 (3)	0.055 (4)	0.003 (3)	0.002 (3)	0.006 (3)
C2	0.035 (3)	0.044 (3)	0.061 (5)	0.008 (3)	−0.004 (3)	0.000 (3)
C3	0.027 (3)	0.047 (3)	0.055 (4)	0.003 (3)	0.003 (3)	−0.003 (3)
C4	0.025 (3)	0.046 (3)	0.051 (4)	0.000 (3)	0.001 (3)	0.000 (3)
C5	0.034 (3)	0.048 (4)	0.066 (5)	−0.006 (3)	0.009 (3)	−0.001 (3)
C6	0.030 (3)	0.048 (4)	0.061 (4)	0.000 (3)	−0.001 (3)	0.003 (3)
C7	0.039 (3)	0.047 (4)	0.064 (5)	−0.005 (3)	0.006 (3)	−0.005 (3)
C8	0.044 (3)	0.052 (4)	0.056 (4)	−0.005 (3)	0.003 (3)	−0.008 (3)
C9	0.037 (3)	0.048 (4)	0.050 (4)	0.004 (3)	0.003 (3)	−0.003 (3)
C10	0.040 (3)	0.058 (4)	0.050 (4)	0.008 (3)	0.007 (3)	0.006 (3)
C11	0.030 (3)	0.047 (3)	0.045 (4)	0.004 (3)	0.003 (3)	−0.006 (3)
C12	0.024 (3)	0.044 (3)	0.048 (4)	0.002 (3)	−0.003 (3)	0.001 (3)
C13	0.030 (3)	0.046 (3)	0.048 (4)	0.000 (3)	−0.002 (3)	0.000 (3)
C14	0.038 (3)	0.038 (3)	0.065 (5)	−0.001 (3)	−0.001 (3)	0.002 (3)
C15	0.032 (3)	0.051 (4)	0.050 (4)	0.001 (3)	−0.005 (3)	0.000 (3)
C16	0.028 (3)	0.064 (4)	0.064 (4)	−0.003 (3)	0.000 (3)	0.000 (4)
C17	0.033 (3)	0.080 (5)	0.066 (5)	0.000 (4)	0.008 (3)	0.008 (4)

Geometric parameters (Å, º) top

O1—C3	1.380 (7)	C7—H7	0.9500
O1—H1	0.8400	C8—C14	1.512 (9)
O2—C4	1.385 (7)	C8—H8	0.9500
O2—C6	1.483 (7)	C9—C14	1.538 (9)
O3—C5	1.442 (8)	C9—C10	1.566 (9)
O3—H3	0.8400	C9—H9	1.0000
N1—C16	1.456 (8)	C10—C11	1.516 (8)
N1—C17	1.460 (8)	C10—H10A	0.9900
N1—C9	1.474 (8)	C10—H10B	0.9900
C1—C2	1.387 (9)	C11—C12	1.371 (8)
C1—C11	1.397 (8)	C12—C13	1.507 (8)
C1—H1A	0.9500	C13—C14	1.511 (9)
C2—C3	1.390 (9)	C13—C15	1.535 (8)
C2—H2	0.9500	C14—H14	1.0000
C3—C4	1.374 (8)	C15—C16	1.512 (8)
C4—C12	1.387 (8)	C15—H15A	0.9900
C5—C7	1.486 (9)	C15—H15B	0.9900
C5—C6	1.542 (8)	C16—H16A	0.9900
C5—H5	1.0000	C16—H16B	0.9900
C6—C13	1.563 (9)	C17—H17A	0.9800
C6—H6	1.0000	C17—H17B	0.9800
C7—C8	1.331 (9)	C17—H17C	0.9800

C3—O1—H1	109.5	C11—C10—C9	114.3 (5)
C4—O2—C6	106.2 (4)	C11—C10—H10A	108.7
C5—O3—H3	109.5	C9—C10—H10A	108.7
C16—N1—C17	112.0 (5)	C11—C10—H10B	108.7
C16—N1—C9	112.2 (5)	C9—C10—H10B	108.7
C17—N1—C9	112.7 (5)	H10A—C10—H10B	107.6
C2—C1—C11	120.1 (6)	C12—C11—C1	117.4 (6)
C2—C1—H1A	119.9	C12—C11—C10	117.9 (5)
C11—C1—H1A	119.9	C1—C11—C10	124.2 (6)
C1—C2—C3	122.3 (6)	C11—C12—C4	121.6 (5)
C1—C2—H2	118.8	C11—C12—C13	126.9 (5)
C3—C2—H2	118.8	C4—C12—C13	110.7 (5)
C4—C3—O1	119.3 (6)	C12—C13—C14	106.5 (5)
C4—C3—C2	116.4 (6)	C12—C13—C15	111.7 (5)
O1—C3—C2	124.1 (5)	C14—C13—C15	110.1 (5)
C3—C4—O2	125.7 (5)	C12—C13—C6	99.5 (5)
C3—C4—C12	121.7 (6)	C14—C13—C6	116.4 (5)
O2—C4—C12	112.4 (5)	C15—C13—C6	112.0 (5)
O3—C5—C7	113.0 (5)	C13—C14—C8	109.8 (5)
O3—C5—C6	108.9 (5)	C13—C14—C9	106.7 (5)
C7—C5—C6	113.5 (5)	C8—C14—C9	114.2 (6)
O3—C5—H5	107.0	C13—C14—H14	108.7
C7—C5—H5	107.0	C8—C14—H14	108.7
C6—C5—H5	107.0	C9—C14—H14	108.7
O2—C6—C5	108.5 (5)	C16—C15—C13	111.9 (5)
O2—C6—C13	107.1 (5)	C16—C15—H15A	109.2
C5—C6—C13	112.8 (5)	C13—C15—H15A	109.2
O2—C6—H6	109.5	C16—C15—H15B	109.2
C5—C6—H6	109.5	C13—C15—H15B	109.2
C13—C6—H6	109.5	H15A—C15—H15B	107.9
C8—C7—C5	121.3 (6)	N1—C16—C15	110.7 (5)
C8—C7—H7	119.4	N1—C16—H16A	109.5
C5—C7—H7	119.4	C15—C16—H16A	109.5
C7—C8—C14	119.7 (6)	N1—C16—H16B	109.5
C7—C8—H8	120.1	C15—C16—H16B	109.5
C14—C8—H8	120.1	H16A—C16—H16B	108.1
N1—C9—C14	107.8 (5)	N1—C17—H17A	109.5
N1—C9—C10	115.3 (5)	N1—C17—H17B	109.5
C14—C9—C10	112.4 (5)	H17A—C17—H17B	109.5
N1—C9—H9	107.0	N1—C17—H17C	109.5
C14—C9—H9	107.0	H17A—C17—H17C	109.5
C10—C9—H9	107.0	H17B—C17—H17C	109.5

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O3ⁱ	0.84	1.96	2.757 (6)	159
O3—H3···O2	0.84	2.17	2.629 (6)	114

Symmetry code: (i) −x, y+1/2, −z+3/2.

Experimental details

Crystal data
Chemical formula	C₁₇H₁₉NO₃
M_r	285.33
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	173
a, b, c (Å)	7.6989 (10), 12.737 (4), 13.740 (4)
V (Å³)	1347.4 (6)
Z	4
Radiation type	Cu Kα
µ (mm⁻¹)	0.78
Crystal size (mm)	0.15 × 0.10 × 0.03

Data collection
Diffractometer	Oxford Diffraction Xcalibur (Ruby, Gemini ultra)
Absorption correction	Multi-scan (CrysAlis PRO; Oxford Diffraction, 2003)
T_min, T_max	0.624, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	13009, 1408, 977
R_int	0.118
(sin θ/λ)_max (Å⁻¹)	0.602

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.068, 0.141, 1.01
No. of reflections	1408
No. of parameters	192
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.27, −0.26

Computer programs: CrysAlis PRO (Oxford Diffraction, 2003), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), XP in SHELXTL (Bruker, 1998) and Mercury (Bruno et al., 2002), publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O3ⁱ	0.84	1.96	2.757 (6)	159.4
O3—H3···O2	0.84	2.17	2.629 (6)	114.4

Symmetry code: (i) −x, y+1/2, −z+3/2.

Footnotes

¹CAS number: 57–27–2.

Acknowledgements

We thank Volker Kahlenberg for access to the X-ray instrument used in this study. DEB acknowledges financial support from the Hertha Firnberg Programme of the Austrian Science Fund (FWF, project No. T593–N19).

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