organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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ISSN: 2056-9890

1,4-Diazo­nia­cyclo­hexane bis­­(3-carb­­oxy­pyrazine-2-carboxyl­ate) dihydrate

aDepartment of Chemistry, School of Sciences, Ferdowsi University of Mashhad, Mashhad 917791436, Iran, and bDepartment of Chemistry, Faculty of Science, Masaryk University, Kamenice 5, Brno, 625 00, Czech Republic
*Correspondence e-mail: heshtiagh@ferdowsi.um.ac.ir, mirzaei487@yahoo.com

(Received 9 September 2010; accepted 7 October 2010; online 13 October 2010)

In the title compound, C4H12N22+·2C6H3N2O4·2H2O or (1,4-dacH2)(pyzdcH)2·2H2O, the complete dication is generated by crystallographic inversion symmetry. An intra­molecular O—H⋯O hydrogen bond occurs in the anion. In the crystal, O—H⋯O, O—H⋯N, N—H⋯O and N—H⋯N hydrogen bonds result in the formation of a three-dimensional network. Additionally, ππ stacking inter­actions between the pyrazine rings with centroid–centroid distances of 3.7065 (2) Å are observed.

Related literature

For related structures dereived from pyrazine-2,3-dicarb­oxy­lic acid with various organic bases, see: Eshtiagh-Hosseini et al. (2010a[Eshtiagh-Hosseini, H., Hassanpoor, A., Canadillas-Delgado, L. & Mirzaei, M. (2010a). Acta Cryst. E66, o1368-o1369.],b[Eshtiagh-Hosseini, H., Gschwind, F., Alfi, N. & Mirzaei, M. (2010b). Acta Cryst. E66, m826-m827.],c[Eshtiagh-Hosseini, H., Aghabozorg, H. & Mirzaei, M. (2010c). Acta Cryst. E66, m882.],d[Eshtiagh-Hosseini, H., Hassanpoor, A., Alfi, N., Mirzaei, M., Fromm, K. M., Shokrollahi, A., Gschwind, F. & Karami, E. (2010d). J. Coord. Chem. 63, 3175-3186.]). For the biological properties of derivatives of 1,4-diazo­nia-cyclo­hexane derivatives, see Iqbal et al. (2001[Iqbal, Z., Nadeem, Q. K., Khan, M. N., Akhtar, M. S. & Waraich, F. N. (2001). Int. J. Agric. Biol. 3, 454-457.]), Greenberg et al. (1981[Greenberg, B. L., Gilman, R. H., Shapiro, H., Gilman, J. B., Mondal, G., Maksud, M., Khatoon, H. & Chowdhury, J. (1981). Am. J. Clin. Nutr. 34, 2508-2516.]).

[Scheme 1]

Experimental

Crystal data
  • C4H12N22+·2C6H3N2O4·2H2O

  • Mr = 458.40

  • Monoclinic, P 21 /c

  • a = 7.7519 (4) Å

  • b = 18.4576 (8) Å

  • c = 7.0292 (4) Å

  • β = 111.974 (6)°

  • V = 932.68 (8) Å3

  • Z = 2

  • Mo Kα radiation

  • μ = 0.14 mm−1

  • T = 120 K

  • 0.40 × 0.40 × 0.30 mm

Data collection
  • Oxford Diffraction Xcalibur diffractometer with a Sapphire2 detector

  • Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Yarnton, England.]) Tmin = 0.990, Tmax = 1.000

  • 4000 measured reflections

  • 2006 independent reflections

  • 1696 reflections with I > 2σ(I)

  • Rint = 0.010

Refinement
  • R[F2 > 2σ(F2)] = 0.033

  • wR(F2) = 0.087

  • S = 1.02

  • 2006 reflections

  • 165 parameters

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

  • Δρmax = 0.24 e Å−3

  • Δρmin = −0.38 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N3—H3B⋯O5i 0.92 (2) 2.01 (2) 2.800 (1) 144 (1)
N3—H3B⋯O4ii 0.92 (2) 2.46 (2) 3.061 (1) 124 (1)
N3—H3A⋯O2 0.92 (2) 1.97 (2) 2.763 (1) 143 (1)
N3—H3A⋯N1 0.92 (2) 2.34 (2) 3.107 (2) 141 (1)
O5—H5B⋯O4iii 0.85 (2) 2.25 (2) 2.923 (1) 136 (2)
O5—H5B⋯N2iii 0.85 (2) 2.34 (2) 3.107 (1) 151 (2)
O5—H5A⋯O2iv 0.95 (2) 1.90 (2) 2.841 (1) 172 (2)
O3—H1O⋯O1 1.13 (2) 1.29 (2) 2.414 (1) 174 (2)
Symmetry codes: (i) x, y, z+1; (ii) [-x+1, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]; (iii) [x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]; (iv) -x+1, -y+1, -z+1.

Data collection: CrysAlis CCD (Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Yarnton, England.]); cell refinement: CrysAlis RED (Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Yarnton, England.]); data reduction: CrysAlis RED; 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: DIAMOND (Crystal Impact, 2009[Crystal Impact (2009). DIAMOND. Crystal Impact GbR, Bonn, Germany.]); software used to prepare material for publication: publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Supporting information


Comment top

1,4-Dac derivatives are a broad class of chemical compounds, many with important pharmacological properties. 1,4-Dac was first introduced as an anthelmimic in 1953 to treat of common roundworms (ascariasis) and pinworms (enterobiasis; oxyuriasis) (Iqbal et al., 2001; Greenberg et al., 1981). The title structure reported herein contains one half of the dicationic fragment (1,4-dacH2)2+, a monoanionic fragment (pyzdcH)- (pyzdcH2 = pyrazine-2,3-dicarboxylic acid) and one solvent water molecule per asymmetric unit (Fig. 1). The center of the 1,4-diazonia-cyclohexane dication represents a crystallographic center of inversion. The crystal structure shows that just one of the protons of pyrazine-2,3-di-carboxylic acid has been transferred to nitrogen atom of the (1,4-dacH2)2+ ring. Hydrogen bond motifs involving anionic and cationic fragments and solvent water molecules result in the formation a one dimensional chain (Fig. 2). As is obvious from the packing diagram additional π···π interactions are present in the crystal structure between adjacent pyrazine rings with centroid-centroid distances of 3.774 Å (Fig. 3).

Related literature top

For related structures dereived from pyrazine-2,3-dicarboxylic acid with various organic bases, see: Eshtiagh-Hosseini et al. (2010a,b,c,d). For the biological properties of derivatives of 1,4-diazonia-cyclohexane derivatives, see Iqbal et al. (2001), Greenberg et al. (1981).

Experimental top

The title compound was synthesized via the reaction between pyzdcH2 (0.20 g, 1.1 mmol) and 1,4-dac (0.10 g, 1.1 mmol) in a aqueous solution (10 ml) stirred for 4 h in 338 K. Slow evaporation of the solvent at r.t. yielded (1,4-dacH2)(pyzdcH)2.2H2O as colorless crystals after one week (yield: 30%).

Refinement top

Carbon bound hydrogen atoms were positioned geometrically and refined as riding using standard SHELXTL constraints, with their Uiso set to 1.2Ueq of their parent atoms. Oxygen and nitrogen bound hydrogen atoms were located in a difference Fourier map and refined isotropically.

Structure description top

1,4-Dac derivatives are a broad class of chemical compounds, many with important pharmacological properties. 1,4-Dac was first introduced as an anthelmimic in 1953 to treat of common roundworms (ascariasis) and pinworms (enterobiasis; oxyuriasis) (Iqbal et al., 2001; Greenberg et al., 1981). The title structure reported herein contains one half of the dicationic fragment (1,4-dacH2)2+, a monoanionic fragment (pyzdcH)- (pyzdcH2 = pyrazine-2,3-dicarboxylic acid) and one solvent water molecule per asymmetric unit (Fig. 1). The center of the 1,4-diazonia-cyclohexane dication represents a crystallographic center of inversion. The crystal structure shows that just one of the protons of pyrazine-2,3-di-carboxylic acid has been transferred to nitrogen atom of the (1,4-dacH2)2+ ring. Hydrogen bond motifs involving anionic and cationic fragments and solvent water molecules result in the formation a one dimensional chain (Fig. 2). As is obvious from the packing diagram additional π···π interactions are present in the crystal structure between adjacent pyrazine rings with centroid-centroid distances of 3.774 Å (Fig. 3).

For related structures dereived from pyrazine-2,3-dicarboxylic acid with various organic bases, see: Eshtiagh-Hosseini et al. (2010a,b,c,d). For the biological properties of derivatives of 1,4-diazonia-cyclohexane derivatives, see Iqbal et al. (2001), Greenberg et al. (1981).

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2009); cell refinement: CrysAlis RED (Oxford Diffraction, 2009); data reduction: CrysAlis RED (Oxford Diffraction, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Crystal Impact, 2009); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. Molecular structure of the constituents of the title compound showing the atom labelling scheme. Thermal ellipsoids are presented at the 50% probability level.
[Figure 2] Fig. 2. A portion of pseudo-1D polymeric chain of the title compound.
[Figure 3] Fig. 3. Crystal packing of the title compound.
1,4-Diazoniacyclohexane bis(3-carboxypyrazine-2-carboxylate) dihydrate top
Crystal data top
C4H12N22+·2C6H3N2O4·2H2OF(000) = 480
Mr = 458.40Dx = 1.632 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 2589 reflections
a = 7.7519 (4) Åθ = 3.0–27.5°
b = 18.4576 (8) ŵ = 0.14 mm1
c = 7.0292 (4) ÅT = 120 K
β = 111.974 (6)°Prism, colourless
V = 932.68 (8) Å30.40 × 0.40 × 0.30 mm
Z = 2
Data collection top
Oxford Diffraction Xcalibur with a Sapphire2 detector
diffractometer
2006 independent reflections
Radiation source: Enhance (Mo) X-ray Source1696 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.010
Detector resolution: 8.4353 pixels mm-1θmax = 27.6°, θmin = 3.0°
ω scanh = 99
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2009)
k = 1523
Tmin = 0.990, Tmax = 1.000l = 68
4000 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.033Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.087H atoms treated by a mixture of independent and constrained refinement
S = 1.02 w = 1/[σ2(Fo2) + (0.0601P)2]
where P = (Fo2 + 2Fc2)/3
2006 reflections(Δ/σ)max = 0.001
165 parametersΔρmax = 0.24 e Å3
0 restraintsΔρmin = 0.38 e Å3
Crystal data top
C4H12N22+·2C6H3N2O4·2H2OV = 932.68 (8) Å3
Mr = 458.40Z = 2
Monoclinic, P21/cMo Kα radiation
a = 7.7519 (4) ŵ = 0.14 mm1
b = 18.4576 (8) ÅT = 120 K
c = 7.0292 (4) Å0.40 × 0.40 × 0.30 mm
β = 111.974 (6)°
Data collection top
Oxford Diffraction Xcalibur with a Sapphire2 detector
diffractometer
2006 independent reflections
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2009)
1696 reflections with I > 2σ(I)
Tmin = 0.990, Tmax = 1.000Rint = 0.010
4000 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0330 restraints
wR(F2) = 0.087H atoms treated by a mixture of independent and constrained refinement
S = 1.02Δρmax = 0.24 e Å3
2006 reflectionsΔρmin = 0.38 e Å3
165 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.66092 (11)0.30115 (5)0.67977 (14)0.0214 (2)
O20.47664 (11)0.38022 (4)0.74880 (14)0.0213 (2)
O30.70151 (11)0.17141 (5)0.70969 (13)0.0198 (2)
O40.54415 (12)0.07636 (5)0.74616 (13)0.0219 (2)
N10.19076 (13)0.29280 (5)0.62615 (15)0.0149 (2)
N20.22265 (13)0.14348 (6)0.61232 (14)0.0156 (2)
N30.15261 (14)0.46005 (6)0.64194 (15)0.0157 (2)
C10.35741 (15)0.26185 (6)0.66012 (16)0.0126 (2)
C20.04412 (16)0.24966 (6)0.58448 (18)0.0159 (3)
H20.07430.27040.56070.019*
C30.05966 (16)0.17478 (7)0.57477 (18)0.0162 (3)
H30.04870.14560.54060.019*
C40.37356 (15)0.18606 (6)0.65666 (17)0.0133 (3)
C50.51081 (16)0.31916 (7)0.70094 (17)0.0151 (3)
C60.55073 (16)0.14025 (7)0.70888 (17)0.0160 (3)
C70.04171 (16)0.44630 (7)0.62525 (19)0.0190 (3)
H7A0.04160.43070.76000.023*
H7B0.09680.40690.52520.023*
C80.15674 (16)0.48597 (7)0.44316 (18)0.0176 (3)
H8A0.10730.44780.33780.021*
H8B0.28680.49610.45880.021*
O50.23627 (12)0.52146 (5)0.03053 (14)0.0190 (2)
H3B0.202 (2)0.4944 (9)0.742 (2)0.027 (4)*
H3A0.222 (2)0.4184 (9)0.675 (2)0.032 (4)*
H5B0.271 (2)0.4805 (10)0.089 (3)0.045 (5)*
H5A0.330 (3)0.5564 (11)0.092 (3)0.071 (6)*
H1O0.683 (3)0.2317 (12)0.687 (3)0.070 (7)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0147 (4)0.0176 (5)0.0344 (5)0.0009 (4)0.0120 (4)0.0005 (4)
O20.0144 (4)0.0146 (5)0.0303 (5)0.0010 (4)0.0032 (4)0.0039 (4)
O30.0130 (4)0.0185 (5)0.0284 (5)0.0008 (4)0.0083 (4)0.0032 (4)
O40.0200 (5)0.0152 (5)0.0284 (5)0.0037 (4)0.0067 (4)0.0011 (4)
N10.0132 (5)0.0164 (5)0.0153 (5)0.0006 (4)0.0054 (4)0.0004 (4)
N20.0157 (5)0.0156 (5)0.0164 (5)0.0010 (4)0.0070 (4)0.0007 (4)
N30.0141 (5)0.0145 (5)0.0166 (5)0.0030 (4)0.0034 (4)0.0006 (4)
C10.0123 (6)0.0155 (6)0.0100 (5)0.0005 (5)0.0041 (4)0.0002 (4)
C20.0117 (6)0.0189 (6)0.0173 (6)0.0016 (5)0.0056 (4)0.0017 (5)
C30.0131 (6)0.0181 (6)0.0176 (6)0.0023 (5)0.0060 (4)0.0002 (5)
C40.0138 (6)0.0158 (6)0.0108 (5)0.0005 (5)0.0052 (4)0.0002 (4)
C50.0132 (6)0.0150 (6)0.0144 (6)0.0005 (5)0.0022 (4)0.0012 (5)
C60.0150 (6)0.0168 (6)0.0149 (6)0.0007 (5)0.0042 (4)0.0041 (4)
C70.0174 (6)0.0179 (6)0.0222 (6)0.0003 (5)0.0080 (5)0.0037 (5)
C80.0158 (6)0.0208 (6)0.0162 (6)0.0024 (5)0.0060 (5)0.0009 (5)
O50.0186 (5)0.0156 (5)0.0215 (5)0.0016 (4)0.0059 (4)0.0002 (4)
Geometric parameters (Å, º) top
O1—C51.2713 (14)C1—C41.4054 (16)
O1—H1O1.29 (2)C1—C51.5362 (16)
O2—C51.2330 (14)C2—C31.3912 (16)
O3—C61.3007 (14)C2—H20.9500
O3—H1O1.13 (2)C3—H30.9500
O4—C61.2133 (15)C4—C61.5359 (16)
N1—C21.3277 (15)C7—C8i1.5061 (17)
N1—C11.3496 (14)C7—H7A0.9900
N2—C31.3230 (15)C7—H7B0.9900
N2—C41.3455 (14)C8—C7i1.5061 (17)
N3—C71.4883 (15)C8—H8A0.9900
N3—C81.4886 (15)C8—H8B0.9900
N3—H3B0.915 (16)O5—H5B0.852 (19)
N3—H3A0.917 (17)O5—H5A0.95 (2)
C5—O1—H1O111.5 (8)C1—C4—C6128.41 (10)
C6—O3—H1O111.6 (10)O2—C5—O1124.78 (11)
C2—N1—C1117.97 (10)O2—C5—C1116.74 (10)
C3—N2—C4118.28 (10)O1—C5—C1118.47 (10)
C7—N3—C8110.95 (9)O4—C6—O3122.63 (11)
C7—N3—H3B107.4 (9)O4—C6—C4118.73 (10)
C8—N3—H3B110.3 (9)O3—C6—C4118.64 (10)
C7—N3—H3A110.9 (9)N3—C7—C8i110.15 (10)
C8—N3—H3A107.0 (9)N3—C7—H7A109.6
H3B—N3—H3A110.4 (14)C8i—C7—H7A109.6
N1—C1—C4120.25 (10)N3—C7—H7B109.6
N1—C1—C5111.37 (10)C8i—C7—H7B109.6
C4—C1—C5128.37 (10)H7A—C7—H7B108.1
N1—C2—C3121.59 (11)N3—C8—C7i110.39 (9)
N1—C2—H2119.2N3—C8—H8A109.6
C3—C2—H2119.2C7i—C8—H8A109.6
N2—C3—C2121.18 (11)N3—C8—H8B109.6
N2—C3—H3119.4C7i—C8—H8B109.6
C2—C3—H3119.4H8A—C8—H8B108.1
N2—C4—C1120.67 (10)H5B—O5—H5A109.8 (17)
N2—C4—C6110.85 (10)
Symmetry code: (i) x, y+1, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N3—H3B···O5ii0.92 (2)2.01 (2)2.800 (1)144 (1)
N3—H3B···O4iii0.92 (2)2.46 (2)3.061 (1)124 (1)
N3—H3A···O20.92 (2)1.97 (2)2.763 (1)143 (1)
N3—H3A···N10.92 (2)2.34 (2)3.107 (2)141 (1)
O5—H5B···O4iv0.85 (2)2.25 (2)2.923 (1)136 (2)
O5—H5B···N2iv0.85 (2)2.34 (2)3.107 (1)151 (2)
O5—H5A···O2v0.95 (2)1.90 (2)2.841 (1)172 (2)
O3—H1O···O11.13 (2)1.29 (2)2.414 (1)174 (2)
Symmetry codes: (ii) x, y, z+1; (iii) x+1, y+1/2, z+3/2; (iv) x, y+1/2, z1/2; (v) x+1, y+1, z+1.

Experimental details

Crystal data
Chemical formulaC4H12N22+·2C6H3N2O4·2H2O
Mr458.40
Crystal system, space groupMonoclinic, P21/c
Temperature (K)120
a, b, c (Å)7.7519 (4), 18.4576 (8), 7.0292 (4)
β (°) 111.974 (6)
V3)932.68 (8)
Z2
Radiation typeMo Kα
µ (mm1)0.14
Crystal size (mm)0.40 × 0.40 × 0.30
Data collection
DiffractometerOxford Diffraction Xcalibur with a Sapphire2 detector
Absorption correctionMulti-scan
(CrysAlis RED; Oxford Diffraction, 2009)
Tmin, Tmax0.990, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections
4000, 2006, 1696
Rint0.010
(sin θ/λ)max1)0.651
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.033, 0.087, 1.02
No. of reflections2006
No. of parameters165
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.24, 0.38

Computer programs: CrysAlis CCD (Oxford Diffraction, 2009), CrysAlis RED (Oxford Diffraction, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Crystal Impact, 2009), publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N3—H3B···O5i0.92 (2)2.01 (2)2.800 (1)144 (1)
N3—H3B···O4ii0.92 (2)2.46 (2)3.061 (1)124 (1)
N3—H3A···O20.92 (2)1.97 (2)2.763 (1)143 (1)
N3—H3A···N10.92 (2)2.34 (2)3.107 (2)141 (1)
O5—H5B···O4iii0.85 (2)2.25 (2)2.923 (1)136 (2)
O5—H5B···N2iii0.85 (2)2.34 (2)3.107 (1)151 (2)
O5—H5A···O2iv0.95 (2)1.90 (2)2.841 (1)172 (2)
O3—H1O···O11.13 (2)1.29 (2)2.414 (1)174 (2)
Symmetry codes: (i) x, y, z+1; (ii) x+1, y+1/2, z+3/2; (iii) x, y+1/2, z1/2; (iv) x+1, y+1, z+1.
 

Acknowledgements

Financial support as well as the provision of X-ray facilities by Ferdowsi University of Mashhad and Masaryk University are gratefully acknowledged by the authors.

References

First citationCrystal Impact (2009). DIAMOND. Crystal Impact GbR, Bonn, Germany.  Google Scholar
First citationEshtiagh-Hosseini, H., Aghabozorg, H. & Mirzaei, M. (2010c). Acta Cryst. E66, m882.  Web of Science CSD CrossRef IUCr Journals Google Scholar
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