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

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 69| Part 7| July 2013| Page o1051
https://doi.org/10.1107/S1600536813015535

2-Methyl-1,2,4-triazolo[4,3-a]pyridin-2-ium tetra­fluoroborate

Siping Wei,a* Li Wanga and Qin Wanga*

aDepartment of Medicinal Chemistry, Luzhou Medical College, Luzhou, Sichuan, 646000, People's Republic of China
*Correspondence e-mail: swei1225@gmail.com, wq_ring@hotmail.com

(Received 8 May 2013; accepted 4 June 2013; online 8 June 2013)

In the title salt, C7H8N3+·BF4−, the 1,2,4-triazolo[4,3-a]pyridinium cation is planar [maximum deviation of 0.016 (2) Å for all non-H atoms]. The cation and anion constitute a tight ionic pair with an F⋯N [2.911 (4) Å] inter­molecular attractive inter­action. The ionic pairs form dimers via stacking inter­actions between inversion-related cations, the normal distance between the cation planes being 3.376 (5) Å. The dimers are packed in stacks along the a axis and linked via C—H⋯F hydrogen bond, forming a three-dimensional network.

Related literature

For catalytic applications of triazoliums, see: Fisher et al. (2006[Fisher, C., Smith, S. W., Powell, D. A. & Fu, G. C. (2006). J. Am. Chem. Soc. 128, 1472-1473.]); Enders et al. (2006[Enders, D., Niemeier, O. & Balensiefer, T. (2006). Angew. Chem. Int. Ed. 45, 1463-1467.]); Wurz et al. (2012[Wurz, N. E., Daniliuc, C. G. & Glorius, F. (2012). Chem. Eur. J. 18, 16297-16301.]). For the synthesis of a related compound and for related structures, see: Ma et al. (2008[Ma, Y., Wei, S., Lan, J., Wang, J., Xie, R. & You, J. (2008). J. Org. Chem. 73, 8256-8264.]); Wei et al. (2009[Wei, S., Liu, B., Zhao, D., Wang, Z., Wu, J., Lan, J. & You, J. (2009). Org. Biomol. Chem. 7, 4241-4247.]).

[Scheme 1]

Experimental

Crystal data

  • C7H8N3+·BF4−

  • Mr = 220.97

  • Orthorhombic, P b c a

  • a = 7.1508 (10) Å

  • b = 12.3070 (18) Å

  • c = 21.431 (3) Å

  • V = 1886.0 (5) Å3

  • Z = 8

  • Mo Kα radiation

  • μ = 0.15 mm−1

  • T = 296 K

  • 0.30 × 0.20 × 0.20 mm
Data collection

  • Oxford Diffraction Xcalibur Eos diffractometer

  • Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2010[Oxford Diffraction (2010). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, England.]) Tmin = 0.956, Tmax = 0.970

  • 14891 measured reflections

  • 1903 independent reflections

  • 1616 reflections with I > 2σ(I)

  • Rint = 0.027
Refinement

  • R[F2 > 2σ(F2)] = 0.077

  • wR(F2) = 0.245

  • S = 1.05

  • 1903 reflections

  • 137 parameters

  • H-atom parameters constrained

  • Δρmax = 0.74 e Å−3

  • Δρmin = −0.50 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A D⋯A D—H⋯A
C1—H1⋯F4i 0.93 2.18 3.086 (3) 165
C5—H5⋯F2ii 0.93 2.38 3.169 (4) 143
C6—H6⋯F1iii 0.93 2.53 3.301 (5) 141
Symmetry codes: (i) [x-{\script{1\over 2}}, y, -z+{\script{3\over 2}}]; (ii) [x-{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]; (iii) x-1, y, z.

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[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: OLEX2 (Dolomanov et al., 2009[Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339-341.]); software used to prepare material for publication: OLEX2.

Supporting information

Crystal structure: contains datablocks luo7, I. DOI: https://doi.org/10.1107/S1600536813015535/kq2005sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536813015535/kq2005Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S1600536813015535/kq2005Isup3.cml

checkCIF report


Comment top

Recently, triazolium salts which can used as carbene precursors are widely using in organic catalysis for the formation of C—C bond reactions, such as benzoin reactions, Stetter reactions and Diels-Alder reactions (Fisher et al. 2006; Enders et al. 2006; Wurz et al. 2012), because of their good stability and excellent catalytic performance. Most research show that bicyclic 1,2,4-triazole carbene have excellent catalytic activity because they have weaker nucleophility than that of thiazole and imidazole carbene.

The crystal structure of the title compound shows that this salt containing the 1,2,4-triazolo[4,3-a]pyridinium cation and tetrafluoroborate anion. The cation adopts the planar structure (r.m.s. deviation is 0.009 Å). The cation and anion constitute a tight ionic pair by the N···F (2.911 (4) Å) intermolecular attractive interaction. The ionic pairs form centrosymmetrical dimers via the intermolecular stacking interactions between cations (the distance between the cation planes within the dimer is 3.376 (5) Å). The dimers are packed in stacks along the a axis and linked into three-dimensional framework by the C—H···F hydrogen bonds.

Related literature top

For catalytic applications of triazoliums, see: Fisher et al. (2006); Enders et al. (2006); Wurz et al. (2012). For the synthesis of a related compound and for related structures, see: Ma et al. (2008); Wei et al. (2009).

Experimental top

The title compound was prepared according to the method of Ma et al. (Ma et al., 2008) and Wei et al. (Wei et al., 2009). A flame-dried round-bottomed flask equipped with a reflux condenser was charged with trimethyloxonium tetrafluoroborate (0.88 g, 6 mmol), 1-(pyridin-2-yl)hydrazine (0.55 g, 5 mmol), and chlorobenzene (20 ml). The mixture was then stirred for 30 min, followed by addition of trimethyl orthoformate (1.65 ml, 15 mmol). After being heated at 110 °C for 10 h, the reaction mixture was concentrated in vacuo. The resulting residue was recrystallized from acetone to give 2-Methylpyrido[1,2-a][1,2,4]-triazol-2-ium tetrafluoroborate as colorless crystal in 88% yield. Mp 171 - 173 °C. 1H NMR (400 MHz, CD3OD) δ 4.40 (s, 3 H), 7.44 (t, J = 7.2 Hz, 1 H), 7.85 - 7.88 (m, 1 H), 7.96 (d, J = 9.6 Hz, 1 H), 8.75 (d, J = 7.8 Hz, 1 H). 13C NMR (100 MHz, CD3OD) δ 40.7, 116.4, 119.8, 127.0, 134.9, 149.5. MS (ESI+) m/z 133 [M - BF4 - H]+. Anal. Calcd for C7H8BF4N3: C, 38.05; H, 3.65; N, 19.02. Found: C, 37.96; H, 3.50; N, 19.25. Colourless crystals suitable for X-ray structural determination were grown by slow evaporation of a solution of the title compound in a petroleum ether/actone mixture (1:1, v/v) at room temperature.

Refinement top

All H atoms were positioned geometrically and refined in the riding model approximation with C—H = 0.93 (CH3) or 0.96 (CH) Å.

BF4- is a tetrahedral anion, the central boron atom is surrounded by four neighboring fluorine atoms. Consequently, the thermal movement of boron atom is limited, but not for the ending fluorine atoms. Therefore, the Ueq for the boron atom is low as compared to the neighboring fluorine atoms.

There are two relatively high positive peaks of 0.74 and 0.53 e/Å3 near the fluorine atoms of the BF4- anion that indicate a slight disorder of the anion. However, due to the low contribution of the second component it was neglected.

Structure description top

Recently, triazolium salts which can used as carbene precursors are widely using in organic catalysis for the formation of C—C bond reactions, such as benzoin reactions, Stetter reactions and Diels-Alder reactions (Fisher et al. 2006; Enders et al. 2006; Wurz et al. 2012), because of their good stability and excellent catalytic performance. Most research show that bicyclic 1,2,4-triazole carbene have excellent catalytic activity because they have weaker nucleophility than that of thiazole and imidazole carbene.

The crystal structure of the title compound shows that this salt containing the 1,2,4-triazolo[4,3-a]pyridinium cation and tetrafluoroborate anion. The cation adopts the planar structure (r.m.s. deviation is 0.009 Å). The cation and anion constitute a tight ionic pair by the N···F (2.911 (4) Å) intermolecular attractive interaction. The ionic pairs form centrosymmetrical dimers via the intermolecular stacking interactions between cations (the distance between the cation planes within the dimer is 3.376 (5) Å). The dimers are packed in stacks along the a axis and linked into three-dimensional framework by the C—H···F hydrogen bonds.

For catalytic applications of triazoliums, see: Fisher et al. (2006); Enders et al. (2006); Wurz et al. (2012). For the synthesis of a related compound and for related structures, see: Ma et al. (2008); Wei et al. (2009).

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: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), showing 50% probability displacement ellipsoids and the atomic numbering.
2-Methyl-1,2,4-triazolo[4,3-a]pyridin-2-ium tetrafluoroborate top
Crystal data top
C7H8N3+·BF4−F(000) = 896
Mr = 220.97Dx = 1.556 Mg m−3
Orthorhombic, PbcaMo Kα radiation, λ = 0.71073 Å
a = 7.1508 (10) ŵ = 0.15 mm−1
b = 12.3070 (18) ÅT = 296 K
c = 21.431 (3) ÅBlock, colourless
V = 1886.0 (5) Å30.30 × 0.20 × 0.20 mm
Z = 8
Data collection top
Oxford Diffraction Xcalibur Eos
diffractometer		1903 independent reflections
Radiation source: fine-focus sealed tube1616 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.027
Detector resolution: 16.0874 pixels mm-1θmax = 26.4°, θmin = 1.9°
ω scansh = −8→8
Absorption correction: multi-scan
(CrysAlis PRO; Oxford Diffraction, 2010)		k = −15→15
Tmin = 0.956, Tmax = 0.970l = −26→26
14891 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)] = 0.077Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.245H-atom parameters constrained
S = 1.05 w = 1/[σ2(Fo2) + (0.1597P)2 + 1.099P]
where P = (Fo2 + 2Fc2)/3
1903 reflections(Δ/σ)max < 0.001
137 parametersΔρmax = 0.74 e Å−3
0 restraintsΔρmin = −0.50 e Å−3
Crystal data top
C7H8N3+·BF4−V = 1886.0 (5) Å3
Mr = 220.97Z = 8
Orthorhombic, PbcaMo Kα radiation
a = 7.1508 (10) ŵ = 0.15 mm−1
b = 12.3070 (18) ÅT = 296 K
c = 21.431 (3) Å0.30 × 0.20 × 0.20 mm
Data collection top
Oxford Diffraction Xcalibur Eos
diffractometer		1903 independent reflections
Absorption correction: multi-scan
(CrysAlis PRO; Oxford Diffraction, 2010)		1616 reflections with I > 2σ(I)
Tmin = 0.956, Tmax = 0.970Rint = 0.027
14891 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0770 restraints
wR(F2) = 0.245H-atom parameters constrained
S = 1.05Δρmax = 0.74 e Å−3
1903 reflectionsΔρmin = −0.50 e Å−3
137 parameters
Special details top

Experimental. Absorption correction: CrysAlis PRO, Agilent Technologies, Version 1.171.35.19, empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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
F10.7647 (5)0.2546 (3)0.66913 (12)0.1094 (10)
F20.5247 (4)0.3344 (2)0.61787 (11)0.1026 (10)
F30.7464 (5)0.4320 (3)0.66199 (16)0.1321 (13)
F40.5444 (4)0.3483 (3)0.72252 (10)0.1119 (10)
N10.1517 (3)0.41555 (15)0.59033 (9)0.0398 (5)
N20.3053 (3)0.57217 (18)0.59455 (10)0.0500 (6)
N30.2503 (3)0.53825 (19)0.65195 (10)0.0500 (6)
C10.1599 (4)0.4458 (2)0.65054 (11)0.0476 (6)
H10.11100.40840.68450.057*
C20.2444 (3)0.49487 (18)0.55689 (11)0.0395 (6)
C30.2603 (3)0.4838 (2)0.49127 (12)0.0486 (7)
H30.32030.53640.46740.058*
C40.1859 (4)0.3948 (2)0.46456 (13)0.0564 (8)
H40.19520.38590.42160.068*
C50.0940 (5)0.3147 (2)0.50043 (15)0.0599 (8)
H50.04540.25380.48050.072*
C60.0751 (4)0.3243 (2)0.56234 (15)0.0544 (7)
H60.01300.27180.58560.065*
C70.2944 (6)0.6039 (3)0.70666 (15)0.0775 (10)
H7A0.22050.66900.70610.116*
H7B0.42470.62270.70610.116*
H7C0.26710.56320.74380.116*
B10.6389 (4)0.3369 (3)0.66829 (12)0.0498 (7)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
F10.126 (2)0.124 (2)0.0777 (16)0.0613 (17)−0.0112 (13)0.0018 (12)
F20.0934 (17)0.150 (2)0.0640 (13)0.0390 (15)−0.0291 (11)−0.0343 (13)
F30.121 (3)0.133 (2)0.142 (3)−0.044 (2)−0.0029 (18)0.0240 (19)
F40.0957 (18)0.191 (3)0.0492 (12)−0.0054 (18)0.0215 (11)−0.0277 (13)
N10.0366 (10)0.0397 (10)0.0431 (10)0.0044 (8)0.0029 (7)0.0056 (7)
N20.0533 (12)0.0509 (12)0.0456 (12)−0.0067 (9)0.0023 (9)0.0053 (9)
N30.0536 (13)0.0574 (13)0.0389 (11)0.0006 (10)0.0010 (8)0.0016 (9)
C10.0477 (14)0.0564 (14)0.0386 (12)0.0048 (11)0.0060 (9)0.0102 (10)
C20.0329 (10)0.0455 (12)0.0401 (13)0.0038 (8)0.0022 (8)0.0082 (9)
C30.0420 (13)0.0621 (15)0.0416 (13)0.0070 (11)0.0045 (10)0.0087 (11)
C40.0525 (15)0.0716 (18)0.0452 (14)0.0193 (13)0.0003 (11)−0.0086 (12)
C50.0613 (17)0.0502 (15)0.0682 (18)0.0065 (12)−0.0054 (14)−0.0129 (12)
C60.0544 (15)0.0413 (12)0.0674 (17)−0.0007 (11)0.0006 (13)0.0023 (11)
C70.096 (3)0.088 (2)0.0488 (16)−0.0100 (19)−0.0080 (17)−0.0151 (15)
B10.0478 (16)0.0710 (19)0.0305 (12)0.0042 (13)0.0016 (10)0.0002 (11)
Geometric parameters (Å, º) top
F1—B11.356 (4)C2—C31.418 (4)
F2—B11.355 (3)C3—C41.345 (4)
F3—B11.407 (5)C3—H30.9300
F4—B11.352 (3)C4—C51.412 (5)
N1—C11.344 (3)C4—H40.9300
N1—C21.380 (3)C5—C61.339 (4)
N1—C61.386 (3)C5—H50.9300
N2—C21.322 (3)C6—H60.9300
N2—N31.357 (3)C7—H7A0.9600
N3—C11.309 (4)C7—H7B0.9600
N3—C71.459 (4)C7—H7C0.9600
C1—H10.9300
C1—N1—C2106.3 (2)C6—C5—C4121.7 (3)
C1—N1—C6131.1 (2)C6—C5—H5119.2
C2—N1—C6122.5 (2)C4—C5—H5119.2
C2—N2—N3103.7 (2)C5—C6—N1117.4 (2)
C1—N3—N2112.9 (2)C5—C6—H6121.3
C1—N3—C7127.4 (2)N1—C6—H6121.3
N2—N3—C7119.7 (3)N3—C7—H7A109.5
N3—C1—N1106.5 (2)N3—C7—H7B109.5
N3—C1—H1126.7H7A—C7—H7B109.5
N1—C1—H1126.7N3—C7—H7C109.5
N2—C2—N1110.5 (2)H7A—C7—H7C109.5
N2—C2—C3130.4 (2)H7B—C7—H7C109.5
N1—C2—C3119.1 (2)F4—B1—F2112.8 (3)
C4—C3—C2118.0 (2)F4—B1—F1113.4 (3)
C4—C3—H3121.0F2—B1—F1113.2 (3)
C2—C3—H3121.0F4—B1—F3105.6 (3)
C3—C4—C5121.4 (3)F2—B1—F3105.8 (3)
C3—C4—H4119.3F1—B1—F3105.1 (3)
C5—C4—H4119.3
C2—N2—N3—C1−0.2 (3)C1—N1—C2—C3179.2 (2)
C2—N2—N3—C7179.7 (3)C6—N1—C2—C30.8 (3)
N2—N3—C1—N1−0.3 (3)N2—C2—C3—C4179.2 (3)
C7—N3—C1—N1179.8 (3)N1—C2—C3—C4−0.9 (3)
C2—N1—C1—N30.7 (3)C2—C3—C4—C50.2 (4)
C6—N1—C1—N3179.0 (2)C3—C4—C5—C60.7 (4)
N3—N2—C2—N10.7 (3)C4—C5—C6—N1−0.9 (4)
N3—N2—C2—C3−179.5 (2)C1—N1—C6—C5−177.9 (3)
C1—N1—C2—N2−0.9 (2)C2—N1—C6—C50.1 (4)
C6—N1—C2—N2−179.3 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C1—H1···F4i0.932.183.086 (3)165
C5—H5···F2ii0.932.383.169 (4)143
C6—H6···F1iii0.932.533.301 (5)141
Symmetry codes: (i) x−1/2, y, −z+3/2; (ii) x−1/2, −y+1/2, −z+1; (iii) x−1, y, z.

Experimental details

Crystal data
Chemical formulaC7H8N3+·BF4−
Mr220.97
Crystal system, space groupOrthorhombic, Pbca
Temperature (K)296
a, b, c (Å)7.1508 (10), 12.3070 (18), 21.431 (3)
V (Å3)1886.0 (5)
Z8
Radiation typeMo Kα
µ (mm−1)0.15
Crystal size (mm)0.30 × 0.20 × 0.20
Data collection
DiffractometerOxford Diffraction Xcalibur Eos
Absorption correctionMulti-scan
(CrysAlis PRO; Oxford Diffraction, 2010)
Tmin, Tmax0.956, 0.970
No. of measured, independent and
observed [I > 2σ(I)] reflections		14891, 1903, 1616
Rint0.027
(sin θ/λ)max (Å−1)0.625
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.077, 0.245, 1.05
No. of reflections1903
No. of parameters137
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å−3)0.74, −0.50

Computer programs: CrysAlis PRO (Oxford Diffraction, 2010), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), OLEX2 (Dolomanov et al., 2009).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C1—H1···F4i0.932.183.086 (3)165
C5—H5···F2ii0.932.383.169 (4)143
C6—H6···F1iii0.932.533.301 (5)141
Symmetry codes: (i) x−1/2, y, −z+3/2; (ii) x−1/2, −y+1/2, −z+1; (iii) x−1, y, z.
 

Acknowledgements

The authors are grateful to the Key Program of the Education Department of Sichuan Province (No. 13ZA0232), the Key Project of Luzhou Medical College (No. 2012ZD-01), the Program for New Century Excellent Talents in University (NCET-10–0945), the Key Project of the Chinese Ministry of Education (No. 211160) and the Scientific Fund of Sichuan Province for Outstanding Young Scientists (No. 2009-26–417) for financial support.

References

First citationDolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339–341.  Web of Science CrossRef CAS IUCr Journals Google Scholar
 First citationEnders, D., Niemeier, O. & Balensiefer, T. (2006). Angew. Chem. Int. Ed. 45, 1463–1467.  Web of Science CrossRef CAS Google Scholar
 First citationFisher, C., Smith, S. W., Powell, D. A. & Fu, G. C. (2006). J. Am. Chem. Soc. 128, 1472–1473.  Web of Science PubMed Google Scholar
 First citationMa, Y., Wei, S., Lan, J., Wang, J., Xie, R. & You, J. (2008). J. Org. Chem. 73, 8256–8264.  Web of Science CSD CrossRef PubMed CAS Google Scholar
 First citationOxford Diffraction (2010). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, England.  Google Scholar
 First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
 First citationWei, S., Liu, B., Zhao, D., Wang, Z., Wu, J., Lan, J. & You, J. (2009). Org. Biomol. Chem. 7, 4241–4247.  Web of Science CSD CrossRef PubMed CAS Google Scholar
 First citationWurz, N. E., Daniliuc, C. G. & Glorius, F. (2012). Chem. Eur. J. 18, 16297–16301.  Web of Science CSD CrossRef CAS PubMed Google Scholar

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Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 69| Part 7| July 2013| Page o1051
https://doi.org/10.1107/S1600536813015535
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