1,3-Bis(pyridin-2-yl)-1H-benzimidazol-3-ium tetra­fluoridoborate

Grieco, G.; Blacque, O.; Berke, H.

doi:10.1107/S1600536811027942

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 67| Part 8| August 2011| Pages o2066-o2067

doi:10.1107/S1600536811027942

Open

access

1,3-Bis(pyridin-2-yl)-1H-benzimidazol-3-ium tetrafluoridoborate

Gabriele Grieco,^a Olivier Blacque ^a ^* and Heinz Berke ^a

^aInstitute of Inorganic Chemistry, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
^*Correspondence e-mail: oblacque@aci.uzh.ch

(Received 29 June 2011; accepted 12 July 2011; online 16 July 2011)

The asymmetric unit of the title compound, C₁₇H₁₃N₄⁺·BF₄⁻, contains one half of the benzimidazolium cation and one half of the tetrafluoridoborate anion, with crystallographic mirror planes bisecting the molecules. One F atom of the tetrafluoridoborate is equally disordered about a crystallographic mirror plane. In the crystal, C—H⋯F interactions link the cations and anions into layers parallel to (100). The crystal packing is further stabilized by F⋯π contacts involving the tetrafluoridoborate anions and the five-membered rings [F⋯centroid = 2.811 (2) Å].

Related literature

For applications of N,N′-bis(2-pyridyl)aryldiamines, see: Stoessel et al. (2010 ); Goldfarb (2009 ) and of imidazolium salts, see: Berlin et al. (2007 ); Bold et al. (2005 ); Huang et al. (2005 ); Murakami et al. (2007 ); Teles et al. (1996 ). For pharmaceuticals based on the aniline–pyridine scaffold, see: Kim et al. (1996 ); Wu et al. (2001 ). For the synthesis of the starting material N,N′-bis(pyridin-2-yl)benzene-1,2-diamine, see: Gdaniec et al. (2004 ).

Experimental

Crystal data

C₁₇H₁₃N₄⁺·BF₄⁻
M_r = 360.12
Orthorhombic, P n m a
a = 7.3412 (2) Å
b = 17.5051 (5) Å
c = 12.2426 (3) Å
V = 1573.28 (7) Å³
Z = 4
Mo Kα radiation
μ = 0.13 mm⁻¹
T = 183 K
0.44 × 0.31 × 0.11 mm

Data collection

Oxford Diffraction Xcalibur diffractometer with a Ruby detector
Absorption correction: analytical [CrysAlis PRO (Oxford Diffraction, 2010 $[Oxford Diffraction (2010). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, England.]$ ) based on Clark & Reid (1995 )] T_min = 0.964, T_max = 0.991
8816 measured reflections
2014 independent reflections
1543 reflections with I > 2σ(I)
R_int = 0.022

Refinement

R[F² > 2σ(F²)] = 0.042
wR(F²) = 0.117
S = 1.08
2014 reflections
130 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.27 e Å⁻³
Δρ_min = −0.36 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C1—H1⋯F3	0.95 (2)	2.14 (2)	3.094 (2)	178 (2)
C9—H9⋯F1ⁱ	0.93	2.62	3.4759 (19)	154
Symmetry code: (i) $[-x+{\script{3\over 2}}, -y, z-{\script{1\over 2}}]$ .

Data collection: CrysAlis PRO (Oxford Diffraction, 2010 $[Oxford Diffraction (2010). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, England.]$ ); 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: Mercury (Macrae et al., 2006 ), ORTEP-3 for Windows (Farrugia, 1997) and POV-RAY for Windows (Cason, 2003 ); software used to prepare material for publication: WinGX (Farrugia, 1999 ) and publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811027942/su2291sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811027942/su2291Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536811027942/su2291Isup3.cml

checkCIF report

Comment top

N,N'-bis(2-pyridyl)aryldiamines are an important class of compounds that are useful as intermediates in the syntheses of organic electroluminescent devices (LED) (Stoessel et al., 2010), or as compounds useful for altering the lifespan of eukaryotic organisms in the yeast (Goldfarb, 2009). Imidazolium salts based on the benzoimidazole scaffold are used in electronics (Bold et al., 2005; Murakami et al., 2007) and in catalytic processes involving the use of the benzimidazolium salt as it is (Teles et al., 1996), or bound to a metal (Berlin et al., 2007; Huang et al., 2005).

We used the N,N'-bis(2-pyridyl)-benzene-1,2-diamine compound as a starting material for the synthesis of the title compound, a new imidazolium salt. Despite the fact that the synthesis of the starting material N,N'-bis(pyridin-2-yl)benzene-1,2-diamine had been reported previously (Gdaniec et al., 2004), we optimized the procedure to obtain a better yield (91 instead of 70%) using the reaction reported in the Experimental section (Fig. 4) with a microwave technique. A similar procedure was succesfully used to synthesize the title compound in a very high yield (99.7%). It is the first example of a coupling between a halo pyridine and an aniline made with microwave heating that does not imply the use of any metal. This method to couple halo pyridines and anilines can be very useful to produce compounds with pharmaceutical activity since many pharmaceuticals are based on the aniline-pyridine scaffold (Kim et al., 1996; Wu et al., 2001).

The asymmetric unit of the title compound, C₁₇H₁₃N₄⁺.BF₄^-, contains one half-molecule of the benzimidazolium cation and one half-molecule of the anion, crystallographic mirror planes bisecting the molecules (Fig. 1). One F atom of the tetrafluoroborate is disordered over two positions. The second position being generated by a crystallographic mirror plane, the site-occupancy factor is 0.5. The benzimidazole and pyridine rings are not coplanar, the dihedral angle between the mean planes is 26.67 (4)°.

In the crystal intermolecular C—H···F interactions link the cations and anions into layers parallel to the (100) crystallographic plane (Fig. 2, Table 1). The crystal packing is further stabilizes by F···π contacts (Fig. 3) involving the tetrafluoridoborate anions and the five-membered rings of the benzimidazole rings [F···centroid = 2.811 (2) Å].

Related literature top

For background to applications of N,N'-bis(2-pyridyl)aryldiamines, see: Stoessel et al. (2010); Goldfarb (2009) and to applications of imidazolium salts, see: Berlin et al. (2007); Bold et al. (2005); Huang et al. (2005); Murakami et al. (2007); Teles et al. (1996). For pharmaceuticals based on the aniline–pyridine scaffold, see: Kim et al. (1996); Wu et al. (2001). For the synthesis of the starting material N,N'-bis(pyridin-2-yl)benzene-1,2-diamine, see: Gdaniec et al. (2004).

Experimental top

To benzene-1,2-diamine (2.7 g, 24.97 mmol) in a microwave vial, 2-chloropyridine (9 ml, 46.95 mmol) was added. The vial was then closed with a cap consisting of a Teflon septum and the reaction mixture was heated for 35 mins at 458 K. Monitoring with TLC (thin layer chromatography) and GC—MS (gas chromatography - mass spectrometry) showed that the benzene-1,2-diamine was consumed after this time and the mixture was allowed to cool to room temperature. The crude mixture was dissolved in water (15 ml) and dropped into a solution of concentrated ammonia in water (25 ml of NH₄OH 24.5% in 250 ml of water). The resulting pink-red precipitate was filtered off, washed with water (50 ml) and was subsequently dried in air to give N,N'-bis(pyridin-2-yl)benzene-1,2-diamine. Further recrystallization from ethanol gave a very pure product (yield: 2.902 g, 91%).

To N,N'-bis(pyridin-2-yl)benzene-1,2-diamine (500 mg, 1.91 mmol) in a microwave vial, finely ground ammonium tetrafluoroborate (204 mg, 1.91 mmol) was added followed by the triethyl orthoformate (10 ml, 59 mmol). The vial with the red pink suspension was then closed with a cap consisting of a Teflon septum and the reaction mixture was heated for 25 minutes at 413 K and then for further 20 minutes to 433 K. After that time inside the vial a blue-violet solid was present and TLC analysis showed that the starting material had been consumed. The solid was separated off and then stirred with ethyl acetate (3x50 ml) for 15 minutes. It was then collected by suction filtration, washed with diethyl ether and dried to afford a deep violet-blue compound (yield: 686 mg, 99.7%). Recrystallization from a hot saturated solution of water/methanol (9/2) afforded red plate-like crystals of the title compound, suitable for X-ray analysis. Spectroscopic data for the title compound are given in the archived CIF.

Computing details top

Data collection: CrysAlis PRO (Oxford Diffraction, 2010); cell refinement: CrysAlis PRO (Oxford Diffraction, 2010); data reduction: CrysAlis PRO (Oxford Diffraction, 2010); 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), ORTEP-3 for Windows (Farrugia, 1997) and POV-RAY for Windows (Cason, 2003); software used to prepare material for publication: WinGX (Farrugia, 1999) and publCIF (Westrip, 2010).

Figures top

	Fig. 1. The molecular structure of the title compound, with the numbering scheme and displacement ellipsoids drawn at the 50% probability level (H-atoms are shown as spheres of arbitrary size). Symmetry code: (i) -x + 3/2, -y, z - 1/2.
	Fig. 2. View normal to (100) of the two-dimensional network of the title compound, formed by intermolecular C—H···F interactions (dashed lines; see Table 1 for details).
	Fig. 3. View normal to (001) of the three-dimensional network of the title compound, formed by intermolecular B—F···π interactions (dashed lines; see Comment section for details).
	Fig. 4. Reaction scheme.

1,3-Bis(pyridin-2-yl)-1H-benzimidazol-3-ium tetrafluoridoborate top

Crystal data top

C₁₇H₁₃N₄⁺·BF₄⁻	F(000) = 736
M_r = 360.12	D_x = 1.52 Mg m⁻³
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 4054 reflections
a = 7.3412 (2) Å	θ = 2.8–32.6°
b = 17.5051 (5) Å	µ = 0.13 mm⁻¹
c = 12.2426 (3) Å	T = 183 K
V = 1573.28 (7) Å³	Plate, red
Z = 4	0.44 × 0.31 × 0.11 mm

Data collection top

Oxford Diffraction Xcalibur diffractometer with a Ruby detector	1543 reflections with I > 2σ(I)
ω scans	R_int = 0.022
Absorption correction: analytical [CrysAlis PRO (Oxford Diffraction, 2010) based on expressions derived by Clark & Reid (1995)]	θ_max = 28.3°, θ_min = 3.2°
T_min = 0.964, T_max = 0.991	h = −9→9
8816 measured reflections	k = −20→23
2014 independent reflections	l = −12→16

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.042	w = 1/[σ²(F_o²) + (0.062P)² + 0.2418P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.117	(Δ/σ)_max < 0.001
S = 1.08	Δρ_max = 0.27 e Å⁻³
2014 reflections	Δρ_min = −0.36 e Å⁻³
130 parameters

Crystal data top

C₁₇H₁₃N₄⁺·BF₄⁻	V = 1573.28 (7) Å³
M_r = 360.12	Z = 4
Orthorhombic, Pnma	Mo Kα radiation
a = 7.3412 (2) Å	µ = 0.13 mm⁻¹
b = 17.5051 (5) Å	T = 183 K
c = 12.2426 (3) Å	0.44 × 0.31 × 0.11 mm

Data collection top

Oxford Diffraction Xcalibur diffractometer with a Ruby detector	2014 independent reflections
Absorption correction: analytical [CrysAlis PRO (Oxford Diffraction, 2010) based on expressions derived by Clark & Reid (1995)]	1543 reflections with I > 2σ(I)
T_min = 0.964, T_max = 0.991	R_int = 0.022
8816 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.042	0 restraints
wR(F²) = 0.117	H atoms treated by a mixture of independent and constrained refinement
S = 1.08	Δρ_max = 0.27 e Å⁻³
2014 reflections	Δρ_min = −0.36 e Å⁻³
130 parameters

Special details top

Experimental. Spectroscopic data for the title compound:

¹H-NMR in CD₃CN: δ = 10.07 (s, 1H), δ = 8.837 (dd, 2H), δ = 8.48 (m, 2H), δ = 8.29 (m,2H), δ = 8.04 (t, 1H), δ = 8.01 (t, 1H), δ = 7.87 (m, 2H) δ = 7.77 (m, 2H).

¹³C-NMR in CD₃CN: δ = 150.95, 141.60, 129.49, 126.93, 118.83, 118.26,116.86.

¹⁹F-NMR in CD₃CN: δ = -152.32.

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	Occ. (<1)
C1	0.7110 (2)	0.25	0.56060 (15)	0.0232 (4)
C2	0.64692 (16)	0.21032 (7)	0.39260 (10)	0.0211 (3)
C3	0.60860 (17)	0.16850 (8)	0.29898 (10)	0.0243 (3)
H3	0.6088	0.1154	0.299	0.029*
C4	0.57020 (17)	0.20992 (8)	0.20603 (11)	0.0263 (3)
H4	0.5436	0.1841	0.1416	0.032*
C5	0.69854 (17)	0.11073 (8)	0.53968 (11)	0.0245 (3)
C6	0.6441 (2)	0.09450 (9)	0.64542 (12)	0.0336 (3)
H6	0.6026	0.1324	0.6925	0.04*
C7	0.6546 (2)	0.01864 (9)	0.67741 (13)	0.0397 (4)
H7	0.622	0.0045	0.748	0.048*
C8	0.7136 (2)	−0.03573 (9)	0.60414 (14)	0.0374 (4)
H8	0.7192	−0.087	0.624	0.045*
C9	0.7640 (2)	−0.01265 (8)	0.50081 (14)	0.0345 (4)
H9	0.8038	−0.0496	0.4517	0.041*
N1	0.68805 (14)	0.18768 (6)	0.49998 (9)	0.0223 (3)
N2	0.75864 (17)	0.06028 (7)	0.46749 (10)	0.0302 (3)
F1	0.58623 (16)	0.18658 (7)	0.89742 (12)	0.0763 (4)
F2	0.8041 (3)	0.2711 (2)	0.98569 (15)	0.0680 (16)	0.5
F3	0.8073 (2)	0.25	0.80661 (11)	0.0577 (4)
B1	0.6969 (3)	0.25	0.89769 (19)	0.0338 (5)
H1	0.743 (3)	0.25	0.6360 (19)	0.024 (5)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0249 (9)	0.0230 (10)	0.0217 (9)	0	−0.0010 (7)	0
C2	0.0210 (6)	0.0224 (7)	0.0200 (6)	0.0008 (5)	0.0019 (5)	0.0021 (5)
C3	0.0254 (6)	0.0229 (7)	0.0245 (7)	−0.0016 (5)	0.0012 (5)	−0.0029 (5)
C4	0.0263 (6)	0.0313 (7)	0.0212 (6)	−0.0013 (5)	0.0002 (5)	−0.0043 (5)
C5	0.0257 (6)	0.0215 (7)	0.0263 (7)	−0.0014 (5)	−0.0046 (5)	0.0030 (5)
C6	0.0450 (8)	0.0289 (8)	0.0269 (7)	−0.0052 (6)	−0.0002 (6)	0.0010 (6)
C7	0.0521 (9)	0.0371 (9)	0.0297 (7)	−0.0092 (7)	−0.0045 (7)	0.0114 (7)
C8	0.0416 (9)	0.0249 (8)	0.0457 (9)	−0.0009 (6)	−0.0092 (7)	0.0117 (7)
C9	0.0388 (8)	0.0235 (8)	0.0411 (8)	0.0055 (6)	−0.0036 (6)	0.0020 (6)
N1	0.0258 (5)	0.0211 (6)	0.0200 (5)	0.0001 (4)	−0.0006 (4)	0.0015 (4)
N2	0.0353 (6)	0.0230 (6)	0.0325 (6)	0.0033 (5)	0.0002 (5)	0.0019 (5)
F1	0.0558 (7)	0.0436 (7)	0.1295 (12)	−0.0010 (5)	0.0195 (7)	0.0143 (7)
F2	0.0400 (9)	0.132 (5)	0.0315 (9)	−0.0042 (12)	−0.0083 (7)	−0.0174 (14)
F3	0.0646 (10)	0.0810 (12)	0.0276 (7)	0	0.0114 (6)	0
B1	0.0284 (11)	0.0494 (16)	0.0236 (11)	0	−0.0016 (9)	0

Geometric parameters (Å, º) top

C1—N1	1.3302 (15)	C6—C7	1.387 (2)
C1—H1	0.95 (2)	C6—H6	0.93
C2—C3	1.3887 (18)	C7—C8	1.378 (2)
C2—C2ⁱ	1.389 (3)	C7—H7	0.93
C2—N1	1.4060 (16)	C8—C9	1.379 (2)
C3—C4	1.3784 (18)	C8—H8	0.93
C3—H3	0.93	C9—N2	1.3408 (19)
C4—C4ⁱ	1.403 (3)	C9—H9	0.93
C4—H4	0.93	F1—B1	1.3756 (18)
C5—N2	1.3249 (18)	F2—B1	1.384 (3)
C5—C6	1.384 (2)	F3—B1	1.379 (3)
C5—N1	1.4341 (17)

N1—C1—N1ⁱ	110.20 (16)	C8—C7—H7	120.2
N1—C1—H1	124.88 (9)	C6—C7—H7	120.2
N1ⁱ—C1—H1	124.88 (9)	C7—C8—C9	118.64 (14)
C3—C2—C2ⁱ	121.81 (8)	C7—C8—H8	120.7
C3—C2—N1	131.81 (12)	C9—C8—H8	120.7
C2ⁱ—C2—N1	106.37 (7)	N2—C9—C8	123.39 (15)
C4—C3—C2	116.46 (13)	N2—C9—H9	118.3
C4—C3—H3	121.8	C8—C9—H9	118.3
C2—C3—H3	121.8	C1—N1—C2	108.53 (11)
C3—C4—C4ⁱ	121.74 (8)	C1—N1—C5	125.06 (12)
C3—C4—H4	119.1	C2—N1—C5	126.39 (11)
C4ⁱ—C4—H4	119.1	C5—N2—C9	116.19 (13)
N2—C5—C6	125.68 (13)	F1—B1—F1ⁱ	107.61 (19)
N2—C5—N1	114.70 (12)	F1—B1—F3	110.21 (13)
C6—C5—N1	119.61 (12)	F1—B1—F2ⁱ	97.01 (18)
C5—C6—C7	116.38 (14)	F1—B1—F2	123.6 (2)
C5—C6—H6	121.8	F1ⁱ—B1—F2	97.01 (18)
C7—C6—H6	121.8	F3—B1—F2	107.17 (18)
C8—C7—C6	119.69 (14)

Symmetry code: (i) x, −y+1/2, z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1···F3	0.95 (2)	2.14 (2)	3.094 (2)	178 (2)
C9—H9···F1ⁱⁱ	0.93	2.62	3.4759 (19)	154

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

Experimental details

Crystal data
Chemical formula	C₁₇H₁₃N₄⁺·BF₄⁻
M_r	360.12
Crystal system, space group	Orthorhombic, Pnma
Temperature (K)	183
a, b, c (Å)	7.3412 (2), 17.5051 (5), 12.2426 (3)
V (Å³)	1573.28 (7)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.13
Crystal size (mm)	0.44 × 0.31 × 0.11

Data collection
Diffractometer	Oxford Diffraction Xcalibur diffractometer with a Ruby detector
Absorption correction	Analytical [CrysAlis PRO (Oxford Diffraction, 2010) based on expressions derived by Clark & Reid (1995)]
T_min, T_max	0.964, 0.991
No. of measured, independent and observed [I > 2σ(I)] reflections	8816, 2014, 1543
R_int	0.022

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.042, 0.117, 1.08
No. of reflections	2014
No. of parameters	130
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.27, −0.36

Computer programs: CrysAlis PRO (Oxford Diffraction, 2010), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), Mercury (Macrae et al., 2006), ORTEP-3 for Windows (Farrugia, 1997) and POV-RAY for Windows (Cason, 2003), WinGX (Farrugia, 1999) and publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1···F3	0.95 (2)	2.14 (2)	3.094 (2)	178.4 (18)
C9—H9···F1ⁱ	0.93	2.62	3.4759 (19)	154

Symmetry code: (i) −x+3/2, −y, z−1/2.

References

Berlin, J. M., Campbell, K., Ritter, T., Funk, T. W., Chlenov, A. & Grubbs, R. H. (2007). Org. Lett. 9, 1339–1342. Web of Science CrossRef PubMed CAS Google Scholar
Bold, M., Lennartz, C., Prinz, M., Schmidt, H.-W., Thelakkat, M., Baete, M., Neuber, C., Kowalsky, W., Schildknecht, C. & Johannes, H.-H. (2005). PCT Int. Appl. WO 2005019373. Google Scholar
Cason, C. J. (2003). POV-RAY. Persistence of Vision Raytracer Pty. Ltd, Victoria, Australia. Google Scholar
Clark, R. C. & Reid, J. S. (1995). Acta Cryst. A51, 887–897. CrossRef CAS Web of Science IUCr Journals Google Scholar
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. CrossRef IUCr Journals Google Scholar
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838. CrossRef CAS IUCr Journals Google Scholar
Gdaniec, M., Bensemann, I. & Połoński, T. (2004). Acta Cryst. C60, o215–o216. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Goldfarb, D. S. (2009). US Patent Appl. Publ. US 20090163545. Google Scholar
Huang, W., Guo, J., Xiao, Y., Zhu, M., Zou, G. & Tang, J. (2005). Tetrahedron, 61, 9783–9790. CrossRef CAS Google Scholar
Kim, H.-J., Han, Y.-H., Chung, S.-J., Lee, M.-H. & Shim, C.-K. (1996). Arch. Pharm. Res. 19, 297–301. CrossRef CAS Web of Science Google Scholar
Macrae, C. F., Edgington, P. R., McCabe, P., Pidcock, E., Shields, G. P., Taylor, R., Towler, M. & van de Streek, J. (2006). J. Appl. Cryst. 39, 453–457. Web of Science CrossRef CAS IUCr Journals Google Scholar
Murakami, T., Yagi, K., Ichijima, S., Igarashi, T. & Satou, T. (2007). WO 2007034985. Google Scholar
Oxford Diffraction (2010). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, England. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Stoessel, P., Heil, H., Joosten, D., Pflumm, C. & Gerhard, A. (2010). PCT Int. Appl. WO 2010099852. Google Scholar
Teles, J. H., Melder, J.-P., Ebel, K., Schneider, R., Gehrer, E., Harder, W., Brode, S., Enders, D., Breuer, K. & Raabe, G. (1996). Helv. Chim. Acta, 79, 61–83. CAS Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar
Wu, S. N., Jan, C. R. & Chiang, H. T. (2001). J. Investig. Med. 49, 522–533. Web of Science CrossRef PubMed CAS Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 67| Part 8| August 2011| Pages o2066-o2067

doi:10.1107/S1600536811027942

Open

access