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ISSN: 2056-9890

2-Amino-1H-benzoimidazol-3-ium 4,4,4-tri­fluoro-1,3-dioxo-1-phenyl­butan-2-ide

aCollege of Chemistry and Chemical Engineering, Xuchang University, Xuchang, Henan Province 461000, People's Republic of China, and bSchool of Chemistry and Chemical Engineering, and Key Laboratory of Biotechnology for Medicinal Plants, Xuzhou Normal University, Xuzhou 221116, People's Republic of China
*Correspondence e-mail: actaeli@mail.google.com

(Received 12 October 2008; accepted 12 November 2008; online 26 November 2008)

In the title compound, C7H8N3+·C10H6F3O2, 1H-benzoimidazol-2-amine system adopts a planar conformation with an r.m.s. deviation of 0.0174 Å. The cation and anion in the asymmetric unit are linked by N—H⋯O hydrogen bonds. There are also additional inter­molecular N—H⋯O hydrogen bonds and ππ stacking inter­actions between the phenyl rings of neighbouring anions with centroid–centroid distances of 4.0976 (13) Å.

Related literature

For details of the bioactivity of organofluorine compounds, see: Hermann et al. (2003[Hermann, B., Erwin, H. & Hansjorg, K. (2003). US Patent No. 2 003 176 284.]); Ulrich (2004[Ulrich, H. (2004). US Patent No. 2 004 033 897.]).

[Scheme 1]

Experimental

Crystal data
  • C7H8N3+·C10H6F3O2

  • Mr = 349.31

  • Orthorhombic, P b c a

  • a = 16.755 (3) Å

  • b = 10.552 (2) Å

  • c = 18.497 (4) Å

  • V = 3270.0 (11) Å3

  • Z = 8

  • Mo Kα radiation

  • μ = 0.12 mm−1

  • T = 113 (2) K

  • 0.12 × 0.10 × 0.06 mm

Data collection
  • Rigaku Saturn CCD diffractometer

  • Absorption correction: multi-scan (CrystalClear; Rigaku/MSC, 2002[Rigaku/MSC (2002). CrystalClear. Rigaku/MSC Inc., The Woodlands, Texas, USA.]) Tmin = 0.986, Tmax = 0.993

  • 31132 measured reflections

  • 2881 independent reflections

  • 2609 reflections with I > 2σ(I)

  • Rint = 0.050

Refinement
  • R[F2 > 2σ(F2)] = 0.039

  • wR(F2) = 0.107

  • S = 1.06

  • 2881 reflections

  • 243 parameters

  • 5 restraints

  • H atoms treated by a mixture of independent and constrained refinement

  • Δρmax = 0.21 e Å−3

  • Δρmin = −0.20 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N1—H1A⋯O2i 0.877 (9) 2.004 (11) 2.7803 (18) 146.8 (16)
N3—H3A⋯O1i 0.895 (9) 1.949 (13) 2.7651 (17) 150.9 (19)
N3—H3A⋯O2i 0.895 (9) 2.363 (18) 2.9912 (18) 127.3 (17)
N1—H1B⋯O1 0.879 (9) 2.030 (10) 2.8662 (18) 158.4 (16)
N2—H2A⋯O2 0.905 (10) 1.862 (11) 2.7360 (18) 161.8 (19)
Symmetry code: (i) [-x+2, y-{\script{1\over 2}}, -z+{\script{1\over 2}}].

Data collection: CrystalClear (Rigaku/MSC, 2002[Rigaku/MSC (2002). CrystalClear. Rigaku/MSC Inc., The Woodlands, Texas, USA.]); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXTL.

Supporting information


Comment top

Compounds that contain fluorine exhibit particular bioactivity, for example, flumioxazin is a widely used herbicide (Hermann et al., 2003; Ulrich,2004). This led us to pay much attention to the synthesis and structure of similar fluoro-compounds. During the synthesis of trifluoromethylated heterocyclic compounds, an intermediate, the title compound,(I), Fig.1, was isolated and we report its crystal structure here.

The 1H-benzo[d]imizol-2-amine cation adopts a planar conformation with an rms deviation of 0.0174 for the fitted atoms. The phenyl ring is almost perpendicular to the fused heterocyclic rings, with a dihedral angle of 81.84 (4)° between them. The cation and anion in the asymmetric unit are linked by N1—H1B···O1 and N2—H2A···O2 hydrogen bonds.

The crystal packing is further stabilized by additional intermolecular N—H···O hydrogen bonds (Table 1, Fig. 2) and intermolecular π···π stacking interactions between the C5-C10 phenyl rings (symmetry code: 2-x, -y, -z) of neighbouring anions with centroid-to-centroid distances, plane-plane distances and displacement distances of 4.0976 (13), 3.786 and 1.565Å respectively.

Related literature top

For details of the bioactivity of organofluorine compounds, see: Hermann et al. (2003); Ulrich (2004).

Experimental top

The title compound was synthesized by the reaction of 4,4,4-trifluoro-1- phenylbutane-1,3-dione (1 mmol) and 1H-benzo[d]imidazol-2-amine (1 mmol) in refluxing ethanol (20 mL) for a certain time (monitored by TLC). Cooling, the reaction mixture slowly to room temperature, gave single crystals suitable for X-ray diffraction.

Refinement top

Hydrogen atoms bound to nitrogen atoms were located in a difference Fourier map and were refined with d(N—H) restrained to 0.90 (1) Å and d(H1A···H1B) restrained to 1.50 (1) Å. Other H atoms were placed in calculated positions, d(C—H) = 0.93 Å, and included in the final cycles of refinement using a riding model, with Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: CrystalClear (Rigaku/MSC, 2002); cell refinement: CrystalClear (Rigaku/MSC, 2002); data reduction: CrystalClear (Rigaku/MSC, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The asymmetric unit of the title compound, showing 30% probability displacement ellipsoids and the atom-numbering scheme. Hydrogen bonds are drawn as dashed lines.
[Figure 2] Fig. 2. The packing diagram of the title compound. Intermolecular hydrogen bonds are shown as dashed lines.
2-Amino-1H-benzoimidazol-3-ium 4,4,4-trifluoro-1,3-dioxo-1-phenylbutan-2-ide top
Crystal data top
C7H8N3+·C10H6F3O2F(000) = 1440
Mr = 349.31Dx = 1.419 Mg m3
Orthorhombic, PbcaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2abCell parameters from 6974 reflections
a = 16.755 (3) Åθ = 2.2–27.9°
b = 10.552 (2) ŵ = 0.12 mm1
c = 18.497 (4) ÅT = 113 K
V = 3270.0 (11) Å3Block, yellow
Z = 80.12 × 0.10 × 0.06 mm
Data collection top
Rigaku Saturn CCD
diffractometer
2881 independent reflections
Radiation source: rotating anode2609 reflections with I > 2σ(I)
Confocal monochromatorRint = 0.050
ω scansθmax = 25.0°, θmin = 2.2°
Absorption correction: multi-scan
(CrystalClear; Rigaku/MSC, 2002)
h = 1919
Tmin = 0.986, Tmax = 0.993k = 1212
31132 measured reflectionsl = 2221
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 atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.107 w = 1/[σ2(Fo2) + (0.0613P)2 + 0.895P]
where P = (Fo2 + 2Fc2)/3
S = 1.06(Δ/σ)max = 0.001
2881 reflectionsΔρmax = 0.21 e Å3
243 parametersΔρmin = 0.20 e Å3
5 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0073 (10)
Crystal data top
C7H8N3+·C10H6F3O2V = 3270.0 (11) Å3
Mr = 349.31Z = 8
Orthorhombic, PbcaMo Kα radiation
a = 16.755 (3) ŵ = 0.12 mm1
b = 10.552 (2) ÅT = 113 K
c = 18.497 (4) Å0.12 × 0.10 × 0.06 mm
Data collection top
Rigaku Saturn CCD
diffractometer
2881 independent reflections
Absorption correction: multi-scan
(CrystalClear; Rigaku/MSC, 2002)
2609 reflections with I > 2σ(I)
Tmin = 0.986, Tmax = 0.993Rint = 0.050
31132 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0395 restraints
wR(F2) = 0.107H atoms treated by a mixture of independent and constrained refinement
S = 1.06Δρmax = 0.21 e Å3
2881 reflectionsΔρmin = 0.20 e Å3
243 parameters
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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
xyzUiso*/Ueq
F10.74257 (7)0.54639 (12)0.05657 (5)0.0552 (3)
F20.77552 (6)0.66729 (9)0.14532 (6)0.0473 (3)
F30.71669 (6)0.49082 (11)0.16580 (6)0.0467 (3)
O11.01117 (6)0.37243 (10)0.11875 (6)0.0301 (3)
O20.88568 (6)0.49842 (10)0.19269 (6)0.0303 (3)
N11.03832 (8)0.19158 (15)0.23172 (8)0.0379 (4)
N20.90662 (8)0.26462 (13)0.25377 (7)0.0298 (3)
N30.94668 (8)0.09546 (13)0.31266 (7)0.0295 (3)
C10.77211 (10)0.54628 (16)0.12397 (9)0.0335 (4)
C20.85307 (9)0.48052 (14)0.13136 (8)0.0277 (3)
C30.88043 (9)0.40780 (15)0.07420 (8)0.0290 (4)
H30.84670.39550.03490.035*
C40.95774 (9)0.35055 (14)0.07232 (8)0.0264 (3)
C50.97828 (9)0.26266 (14)0.01141 (8)0.0263 (3)
C61.05759 (10)0.25313 (16)0.01066 (9)0.0324 (4)
H61.09620.30300.01160.039*
C71.07968 (10)0.17084 (17)0.06508 (10)0.0378 (4)
H71.13270.16650.07970.045*
C81.02270 (11)0.09443 (16)0.09797 (9)0.0368 (4)
H81.03760.03790.13410.044*
C90.94389 (10)0.10278 (15)0.07679 (9)0.0346 (4)
H90.90570.05180.09890.042*
C100.92111 (10)0.18696 (15)0.02263 (8)0.0308 (4)
H100.86780.19280.00910.037*
C110.96806 (9)0.18451 (15)0.26443 (8)0.0296 (4)
C120.84329 (9)0.22790 (15)0.29854 (8)0.0275 (4)
C130.76879 (9)0.28105 (17)0.31021 (8)0.0321 (4)
H130.75180.35270.28530.038*
C140.72078 (10)0.22158 (17)0.36124 (9)0.0349 (4)
H140.67050.25480.37100.042*
C150.74579 (10)0.11347 (17)0.39833 (9)0.0339 (4)
H150.71180.07630.43190.041*
C160.82038 (10)0.06027 (15)0.38614 (8)0.0309 (4)
H160.83710.01200.41060.037*
C170.86862 (9)0.11999 (14)0.33575 (8)0.0273 (3)
H1A1.0783 (9)0.1439 (16)0.2457 (10)0.046 (5)*
H1B1.0438 (10)0.2461 (14)0.1961 (8)0.043 (5)*
H2A0.9093 (12)0.3377 (13)0.2283 (10)0.051 (6)*
H3A0.9769 (11)0.0317 (15)0.3290 (11)0.051 (6)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
F10.0509 (7)0.0792 (8)0.0356 (6)0.0313 (6)0.0129 (5)0.0053 (6)
F20.0462 (6)0.0331 (6)0.0628 (7)0.0093 (4)0.0013 (5)0.0034 (5)
F30.0293 (5)0.0561 (7)0.0546 (7)0.0022 (5)0.0024 (5)0.0043 (5)
O10.0292 (6)0.0319 (6)0.0291 (6)0.0017 (5)0.0052 (5)0.0008 (5)
O20.0307 (6)0.0322 (6)0.0279 (6)0.0019 (5)0.0042 (4)0.0015 (5)
N10.0316 (8)0.0461 (9)0.0358 (8)0.0102 (7)0.0039 (6)0.0122 (7)
N20.0306 (7)0.0313 (7)0.0274 (7)0.0048 (6)0.0006 (5)0.0055 (6)
N30.0298 (7)0.0304 (7)0.0284 (7)0.0056 (6)0.0008 (5)0.0029 (6)
C10.0353 (9)0.0355 (9)0.0296 (8)0.0026 (7)0.0016 (7)0.0005 (7)
C20.0275 (8)0.0253 (8)0.0301 (8)0.0030 (6)0.0033 (6)0.0048 (6)
C30.0295 (8)0.0312 (8)0.0263 (8)0.0009 (6)0.0056 (6)0.0006 (6)
C40.0296 (8)0.0239 (8)0.0256 (7)0.0038 (6)0.0027 (6)0.0053 (6)
C50.0291 (8)0.0251 (7)0.0249 (7)0.0002 (6)0.0030 (6)0.0044 (6)
C60.0285 (8)0.0337 (9)0.0350 (9)0.0024 (7)0.0036 (7)0.0011 (7)
C70.0309 (9)0.0418 (10)0.0407 (9)0.0010 (7)0.0045 (7)0.0035 (8)
C80.0452 (10)0.0324 (9)0.0327 (9)0.0025 (7)0.0014 (7)0.0036 (7)
C90.0391 (9)0.0286 (8)0.0360 (9)0.0057 (7)0.0058 (7)0.0025 (7)
C100.0287 (8)0.0306 (8)0.0330 (8)0.0030 (6)0.0021 (6)0.0020 (7)
C110.0301 (9)0.0336 (8)0.0250 (8)0.0036 (7)0.0028 (6)0.0009 (6)
C120.0293 (8)0.0305 (8)0.0227 (7)0.0001 (6)0.0027 (6)0.0021 (6)
C130.0300 (9)0.0369 (9)0.0292 (8)0.0055 (7)0.0047 (6)0.0011 (7)
C140.0260 (8)0.0453 (10)0.0332 (9)0.0007 (7)0.0029 (6)0.0045 (8)
C150.0300 (8)0.0421 (10)0.0298 (8)0.0074 (7)0.0005 (7)0.0015 (7)
C160.0348 (9)0.0300 (8)0.0279 (8)0.0032 (7)0.0049 (6)0.0018 (6)
C170.0279 (8)0.0290 (8)0.0249 (7)0.0008 (6)0.0056 (6)0.0033 (6)
Geometric parameters (Å, º) top
F1—C11.3415 (19)C5—C101.397 (2)
F2—C11.338 (2)C6—C71.380 (2)
F3—C11.3429 (19)C6—H60.9300
O1—C41.2618 (18)C7—C81.390 (3)
O2—C21.2732 (18)C7—H70.9300
N1—C111.326 (2)C8—C91.380 (2)
N1—H1A0.877 (9)C8—H80.9300
N1—H1B0.879 (9)C9—C101.392 (2)
N2—C111.346 (2)C9—H90.9300
N2—C121.401 (2)C10—H100.9300
N2—H2A0.905 (10)C12—C131.385 (2)
N3—C111.344 (2)C12—C171.396 (2)
N3—C171.400 (2)C13—C141.390 (2)
N3—H3A0.895 (9)C13—H130.9300
C1—C21.530 (2)C14—C151.395 (2)
C2—C31.385 (2)C14—H140.9300
C3—C41.430 (2)C15—C161.388 (2)
C3—H30.9300C15—H150.9300
C4—C51.499 (2)C16—C171.385 (2)
C5—C61.394 (2)C16—H160.9300
C11—N1—H1A120.8 (12)C8—C7—H7120.0
C11—N1—H1B118.1 (11)C9—C8—C7119.73 (16)
H1A—N1—H1B121.1 (14)C9—C8—H8120.1
C11—N2—C12108.60 (13)C7—C8—H8120.1
C11—N2—H2A125.0 (13)C8—C9—C10120.49 (15)
C12—N2—H2A125.5 (13)C8—C9—H9119.8
C11—N3—C17108.79 (13)C10—C9—H9119.8
C11—N3—H3A126.8 (14)C9—C10—C5120.07 (15)
C17—N3—H3A124.4 (14)C9—C10—H10120.0
F2—C1—F1106.81 (13)C5—C10—H10120.0
F2—C1—F3105.99 (13)N1—C11—N3125.36 (14)
F1—C1—F3106.30 (13)N1—C11—N2125.23 (15)
F2—C1—C2111.64 (13)N3—C11—N2109.40 (14)
F1—C1—C2114.24 (14)C13—C12—C17121.81 (14)
F3—C1—C2111.35 (13)C13—C12—N2131.50 (15)
O2—C2—C3128.36 (14)C17—C12—N2106.66 (13)
O2—C2—C1113.13 (14)C12—C13—C14116.39 (15)
C3—C2—C1118.47 (14)C12—C13—H13121.8
C2—C3—C4123.55 (14)C14—C13—H13121.8
C2—C3—H3118.2C13—C14—C15121.95 (15)
C4—C3—H3118.2C13—C14—H14119.0
O1—C4—C3123.29 (14)C15—C14—H14119.0
O1—C4—C5117.51 (13)C16—C15—C14121.39 (15)
C3—C4—C5119.18 (13)C16—C15—H15119.3
C6—C5—C10118.71 (14)C14—C15—H15119.3
C6—C5—C4118.92 (13)C17—C16—C15116.78 (15)
C10—C5—C4122.34 (14)C17—C16—H16121.6
C7—C6—C5120.98 (15)C15—C16—H16121.6
C7—C6—H6119.5C16—C17—C12121.68 (14)
C5—C6—H6119.5C16—C17—N3131.78 (14)
C6—C7—C8120.01 (16)C12—C17—N3106.52 (13)
C6—C7—H7120.0
F2—C1—C2—O248.38 (18)C4—C5—C10—C9177.14 (14)
F1—C1—C2—O2169.71 (14)C17—N3—C11—N1179.40 (15)
F3—C1—C2—O269.86 (17)C17—N3—C11—N21.38 (17)
F2—C1—C2—C3133.69 (15)C12—N2—C11—N1179.13 (15)
F1—C1—C2—C312.4 (2)C12—N2—C11—N31.64 (18)
F3—C1—C2—C3108.07 (16)C11—N2—C12—C13177.01 (16)
O2—C2—C3—C47.8 (3)C11—N2—C12—C171.26 (17)
C1—C2—C3—C4174.64 (14)C17—C12—C13—C140.3 (2)
C2—C3—C4—O18.1 (2)N2—C12—C13—C14177.71 (16)
C2—C3—C4—C5173.70 (14)C12—C13—C14—C150.6 (2)
O1—C4—C5—C627.7 (2)C13—C14—C15—C160.3 (2)
C3—C4—C5—C6150.58 (15)C14—C15—C16—C170.3 (2)
O1—C4—C5—C10150.25 (14)C15—C16—C17—C120.5 (2)
C3—C4—C5—C1031.4 (2)C15—C16—C17—N3177.26 (15)
C10—C5—C6—C70.1 (2)C13—C12—C17—C160.2 (2)
C4—C5—C6—C7178.13 (15)N2—C12—C17—C16178.68 (14)
C5—C6—C7—C81.0 (3)C13—C12—C17—N3178.06 (14)
C6—C7—C8—C91.1 (3)N2—C12—C17—N30.42 (16)
C7—C8—C9—C100.1 (3)C11—N3—C17—C16177.45 (16)
C8—C9—C10—C50.8 (2)C11—N3—C17—C120.57 (16)
C6—C5—C10—C90.9 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···O2i0.88 (1)2.00 (1)2.7803 (18)147 (2)
N3—H3A···O1i0.90 (1)1.95 (1)2.7651 (17)151 (2)
N3—H3A···O2i0.90 (1)2.36 (2)2.9912 (18)127 (2)
N1—H1B···O10.88 (1)2.03 (1)2.8662 (18)158 (2)
N2—H2A···O20.91 (1)1.86 (1)2.7360 (18)162 (2)
Symmetry code: (i) x+2, y1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaC7H8N3+·C10H6F3O2
Mr349.31
Crystal system, space groupOrthorhombic, Pbca
Temperature (K)113
a, b, c (Å)16.755 (3), 10.552 (2), 18.497 (4)
V3)3270.0 (11)
Z8
Radiation typeMo Kα
µ (mm1)0.12
Crystal size (mm)0.12 × 0.10 × 0.06
Data collection
DiffractometerRigaku Saturn CCD
diffractometer
Absorption correctionMulti-scan
(CrystalClear; Rigaku/MSC, 2002)
Tmin, Tmax0.986, 0.993
No. of measured, independent and
observed [I > 2σ(I)] reflections
31132, 2881, 2609
Rint0.050
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.039, 0.107, 1.06
No. of reflections2881
No. of parameters243
No. of restraints5
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.21, 0.20

Computer programs: CrystalClear (Rigaku/MSC, 2002), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···O2i0.877 (9)2.004 (11)2.7803 (18)146.8 (16)
N3—H3A···O1i0.895 (9)1.949 (13)2.7651 (17)150.9 (19)
N3—H3A···O2i0.895 (9)2.363 (18)2.9912 (18)127.3 (17)
N1—H1B···O10.879 (9)2.030 (10)2.8662 (18)158.4 (16)
N2—H2A···O20.905 (10)1.862 (11)2.7360 (18)161.8 (19)
Symmetry code: (i) x+2, y1/2, z+1/2.
 

Acknowledgements

The authors thank the Natural Science Foundation of Henan Province, China (grant No. 082300420110) and the Natural Science Foundation of Henan Province Education Department, China (grant No. 2007150036) for financial support.

References

First citationHermann, B., Erwin, H. & Hansjorg, K. (2003). US Patent No. 2 003 176 284.  Google Scholar
First citationRigaku/MSC (2002). CrystalClear. Rigaku/MSC Inc., The Woodlands, Texas, USA.  Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationUlrich, H. (2004). US Patent No. 2 004 033 897.  Google Scholar

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