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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 1| January 2013| Page o126
https://doi.org/10.1107/S1600536812050994

Triclinic polymorph of 4-[4-(4-formyl­phen­­oxy)but­­oxy]benzaldehyde

Tomislav Balić,a* Berislav Markovića and Ivana Balića

aDepartment of Chemistry, J. J. Strossmayer University, Osijek, Franje Kuhača 20, HR-31000 Osijek, Croatia
*Correspondence e-mail: tombalic@kemija.unios.hr

(Received 23 November 2012; accepted 16 December 2012; online 22 December 2012)

The title compound, C18H18O4, is a triclinic polymorph of the previously reported monoclinic polymorph [Han & Zhen (2005[Han, J.-R. & Zhen, X.-L. (2005). Acta Cryst. E61, o4358-o4359.]). Acta Cryst. E61, o4358–o4359]. In the crystal of the triclinic polymorph, molecules are linked by two pairs of C—H⋯O hydrogen bonds, forming a two-dimensional network parallel to (102), and enclosing loops with graph set motifs of R22(8) and R22(6).

Related literature

For the monoclinic polymorph, see: Han & Zhen (2005[Han, J.-R. & Zhen, X.-L. (2005). Acta Cryst. E61, o4358-o4359.]). For related structures and the synthesis of similar compounds, see: Balić et al. (2012[Balić, T., Marković, B. & Balić, I. (2012). Acta Cryst. E68, o2664.]); Ma & Cao (2011[Ma, Z. & Cao, Y. (2011). Acta Cryst. E67, o1503.]); Dehno Khalaji et al. (2011[Dehno Khalaji, A., Hafez Ghoran, S., Gotoh, K. & Ishida, H. (2011). Acta Cryst. E67, o2484.]); Narasimha Moorthy et al. (2005[Narasimha Moorthy, J., Natarajan, R. & Venugopalan, P. (2005). J. Mol. Struct. 741, 107-114.]); Ilhan et al. (2007[Ilhan, S., Temel, H., Yilmaz, I. & Kilic, A. (2007). Transition Met. Chem. 32, 344-349.]). For graph-set analysis of hydrogen bonds, see Bernstein et al. (1995[Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555-1573.]).

[Scheme 1]

Experimental

Crystal data

  • C18H18O4

  • Mr = 298.32

  • Triclinic, [P \overline 1]

  • a = 4.4969 (2) Å

  • b = 7.9507 (6) Å

  • c = 11.0679 (8) Å

  • α = 73.854 (6)°

  • β = 84.788 (5)°

  • γ = 80.903 (5)°

  • V = 374.86 (4) Å3

  • Z = 1

  • Mo Kα radiation

  • μ = 0.09 mm−1

  • T = 190 K

  • 0.59 × 0.35 × 0.21 mm
Data collection

  • Oxford Diffraction Xcalibur Sapphire3 diffractometer

  • Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, England.]) Tmin = 0.683, Tmax = 1.000

  • 2235 measured reflections

  • 1473 independent reflections

  • 1272 reflections with I > 2σ(I)

  • Rint = 0.010
Refinement

  • R[F2 > 2σ(F2)] = 0.043

  • wR(F2) = 0.123

  • S = 1.04

  • 1473 reflections

  • 100 parameters

  • H-atom parameters constrained

  • Δρmax = 0.29 e Å−3

  • Δρmin = −0.17 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A D⋯A D—H⋯A
C6—H6⋯O2i 0.95 2.58 3.4985 (16) 162
C1—H1⋯O1ii 0.95 2.59 3.3953 (18) 143
Symmetry codes: (i) -x+2, -y, -z+1; (ii) -x, -y-1, -z+2.

Data collection: CrysAlis PRO (Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, England.]); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SIR2004 (Burla et al., 2005[Burla, M. C., Caliandro, R., Camalli, M., Carrozzini, B., Cascarano, G. L., De Caro, L., Giacovazzo, C., Polidori, G. & Spagna, R. (2005). J. Appl. Cryst. 38, 381-388.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: ORTEP-3 (Farrugia, 2012[Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849-854.]); software used to prepare material for publication: WinGX (Farrugia, 2012[Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849-854.]), PARST97 (Nardelli, 1995[Nardelli, M. (1995). J. Appl. Cryst. 28, 659.]) and Mercury (Macrae et al., 2006[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.]).

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536812050994/ng5308sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536812050994/ng5308Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S1600536812050994/ng5308Isup3.cml

checkCIF report


Comment top

Reacent structural studies of dialdehydes (Balić et al. 2012; Narasimha Moorthy et al. 2005), or the so called two-arm aldehydes have proposed them as potential precursors for condensation reactions with primary amines (Ilhan et al. 2007; Ma & Cao 2011; Dehno Khalaji et al. 2011). In a relation to this structural studies a new triclinic polymorph of title compound was found. Previously reported monoclinic polymorph (Han & Zhen 2005) was reported in P21/c space group with Z=2. The new polymorph was found in P1 space group (Z=1), with different intermolecular interactions (Figure 1.).

The original polymorph crystallize in monoclinic space group P21/c, with a = 7.988 (2), b = 6.6635 (16), c= 14.260 (4) Å, β= 96.354 (4)° and Z = 2 (Han & Zhen 2005). The title compound crystallizes in the space group P1 with a = 4.5749 (7), b= 7.9467 (10), c = 14.260 (4) Å, α= 73.597 (11)°, β = 83.154 (11)°, γ = 80.533 (12)° and Z = 1. In the reported structure crystallographic inversion centre lies in the center of the molecule, so the asymmetric unit comprises only one half of the molecule. The molecular structure of the title compound is shown in Figure 2. In the triclinic polymorph the molecules are linked in centrosymetric dimers via weak C1— H1···O1 intermolecular interactions, as previously reported by Narasimha Moorthy et al. (2005) and Balić et al. (2012). Additional stabilization of crystal structure is accomplished by weak C4— H4···O2 (Figure 1.). In the previously reported monoclinic polymorph the dihedral angle between benzaldehyde group and four central carbon atoms is 62.82°, while in triclinic polymorph this angle is 42.07°. However, the largest difference between these two polymorphs is manifested by the presence of R22(6) and R22(8) (Bernstein et al. 1995) supramolecular motifs in the triclinic polymorph.

Related literature top

For the monoclinic polymorph, see: Han & Zhen (2005). For related structures and the synthesis of similar compounds, see: Balić et al. (2012); Ma & Cao (2011); Dehno Khalaji et al. (2011); Narasimha Moorthy et al. (2005); Ilhan et al. (2007). For graph-set analysis of hydrogen bonds, see Bernstein et al. (1995).

Experimental top

The title compound was prepared by folowing procedure: p-hydroxybenzaldehyde (50 mmol) and K2CO3 (50 mmol) were mixed in DMF and the mixture was brought to brisk reflux. 25 mmol of butane-1,4-dibrom dissolved in DMF was then added and the reaction mixture was refluxed for 5 h. After the reaction was complete, 100 ml of water was added and the resulting percipitate was filtered and washed with water. Single crystals suitable for X-ray diffraction were grown via slow evaporation from ethanol solution of the title compound.

Refinement top

All H atoms, were positioned geometrically and refined using a riding model with C—H = 0.93 - 0.97 Å and with Uiso(H) = 1.2 times Ueq(C).

Structure description top

Reacent structural studies of dialdehydes (Balić et al. 2012; Narasimha Moorthy et al. 2005), or the so called two-arm aldehydes have proposed them as potential precursors for condensation reactions with primary amines (Ilhan et al. 2007; Ma & Cao 2011; Dehno Khalaji et al. 2011). In a relation to this structural studies a new triclinic polymorph of title compound was found. Previously reported monoclinic polymorph (Han & Zhen 2005) was reported in P21/c space group with Z=2. The new polymorph was found in P1 space group (Z=1), with different intermolecular interactions (Figure 1.).

The original polymorph crystallize in monoclinic space group P21/c, with a = 7.988 (2), b = 6.6635 (16), c= 14.260 (4) Å, β= 96.354 (4)° and Z = 2 (Han & Zhen 2005). The title compound crystallizes in the space group P1 with a = 4.5749 (7), b= 7.9467 (10), c = 14.260 (4) Å, α= 73.597 (11)°, β = 83.154 (11)°, γ = 80.533 (12)° and Z = 1. In the reported structure crystallographic inversion centre lies in the center of the molecule, so the asymmetric unit comprises only one half of the molecule. The molecular structure of the title compound is shown in Figure 2. In the triclinic polymorph the molecules are linked in centrosymetric dimers via weak C1— H1···O1 intermolecular interactions, as previously reported by Narasimha Moorthy et al. (2005) and Balić et al. (2012). Additional stabilization of crystal structure is accomplished by weak C4— H4···O2 (Figure 1.). In the previously reported monoclinic polymorph the dihedral angle between benzaldehyde group and four central carbon atoms is 62.82°, while in triclinic polymorph this angle is 42.07°. However, the largest difference between these two polymorphs is manifested by the presence of R22(6) and R22(8) (Bernstein et al. 1995) supramolecular motifs in the triclinic polymorph.

For the monoclinic polymorph, see: Han & Zhen (2005). For related structures and the synthesis of similar compounds, see: Balić et al. (2012); Ma & Cao (2011); Dehno Khalaji et al. (2011); Narasimha Moorthy et al. (2005); Ilhan et al. (2007). For graph-set analysis of hydrogen bonds, see Bernstein et al. (1995).

Computing details top

Data collection: CrysAlis PRO (Oxford Diffraction, 2009); cell refinement: CrysAlis PRO (Oxford Diffraction, 2009); data reduction: CrysAlis PRO (Oxford Diffraction, 2009); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012), PARST97 (Nardelli, 1995) and Mercury (Macrae et al., 2006).

Figures top
[Figure 1] Fig. 1. Crystal packing of title compound viewed down the a axis with dased lines representing weak C— H···O [graph set R22(6), R22(8)] intermolecular interactions.
[Figure 2] Fig. 2. The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
4-[4-(4-Formylphenoxy)butoxy]benzaldehyde top
Crystal data top
C18H18O4Z = 1
Mr = 298.32F(000) = 158
Triclinic, P1Dx = 1.321 Mg m−3
a = 4.4969 (2) ÅMo Kα radiation, λ = 0.7107 Å
b = 7.9507 (6) ÅCell parameters from 1657 reflections
c = 11.0679 (8) Åθ = 4.6–28.5°
α = 73.854 (6)°µ = 0.09 mm−1
β = 84.788 (5)°T = 190 K
γ = 80.903 (5)°Block, colourless
V = 374.86 (4) Å30.59 × 0.35 × 0.21 mm
Data collection top
Oxford Diffraction Xcalibur Sapphire3
diffractometer		1473 independent reflections
Radiation source: Enhance (Mo) X-ray Source1272 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.010
Detector resolution: 16.3426 pixels mm-1θmax = 26.0°, θmin = 4.6°
ω scansh = −5→4
Absorption correction: multi-scan
(CrysAlis PRO; Oxford Diffraction, 2009)		k = −9→9
Tmin = 0.683, Tmax = 1.000l = −13→13
2235 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)] = 0.043Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.123H-atom parameters constrained
S = 1.04 w = 1/[σ2(Fo2) + (0.0676P)2 + 0.0807P]
where P = (Fo2 + 2Fc2)/3
1473 reflections(Δ/σ)max < 0.001
100 parametersΔρmax = 0.29 e Å−3
0 restraintsΔρmin = −0.17 e Å−3
Crystal data top
C18H18O4γ = 80.903 (5)°
Mr = 298.32V = 374.86 (4) Å3
Triclinic, P1Z = 1
a = 4.4969 (2) ÅMo Kα radiation
b = 7.9507 (6) ŵ = 0.09 mm−1
c = 11.0679 (8) ÅT = 190 K
α = 73.854 (6)°0.59 × 0.35 × 0.21 mm
β = 84.788 (5)°
Data collection top
Oxford Diffraction Xcalibur Sapphire3
diffractometer		1473 independent reflections
Absorption correction: multi-scan
(CrysAlis PRO; Oxford Diffraction, 2009)		1272 reflections with I > 2σ(I)
Tmin = 0.683, Tmax = 1.000Rint = 0.010
2235 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0430 restraints
wR(F2) = 0.123H-atom parameters constrained
S = 1.04Δρmax = 0.29 e Å−3
1473 reflectionsΔρmin = −0.17 e Å−3
100 parameters
Special details top

Experimental. (CrysAlis PRO RED; Oxford Diffraction, 2009)

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
O10.2410 (3)−0.49759 (14)0.85962 (11)0.0490 (4)
O20.8584 (2)0.19238 (11)0.61242 (8)0.0289 (3)
C10.2367 (3)−0.3608 (2)0.88964 (14)0.0377 (4)
H10.1248−0.34960.96470.045*
C20.3920 (3)−0.21240 (17)0.81809 (13)0.0283 (3)
C30.3932 (3)−0.06701 (18)0.86379 (12)0.0308 (3)
H30.2870−0.06270.94130.037*
C40.5460 (3)0.07238 (17)0.79893 (12)0.0280 (3)
H40.54530.17110.83150.034*
C50.7004 (3)0.06505 (16)0.68513 (12)0.0242 (3)
C60.6963 (3)−0.07927 (18)0.63690 (13)0.0292 (3)
H60.7991−0.08310.55860.035*
C70.5437 (3)−0.21533 (17)0.70273 (13)0.0305 (3)
H70.5410−0.31300.66940.037*
C80.8898 (3)0.33927 (16)0.65981 (12)0.0268 (3)
H8A0.99140.29700.74060.032*
H8B0.68920.40450.67420.032*
C91.0762 (3)0.45809 (17)0.56216 (12)0.0276 (3)
H9A1.27080.38830.54570.033*
H9B1.12060.55320.59670.033*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0659 (8)0.0366 (7)0.0488 (7)−0.0282 (5)0.0138 (6)−0.0119 (5)
O20.0378 (5)0.0208 (5)0.0297 (5)−0.0128 (4)0.0082 (4)−0.0076 (4)
C10.0431 (8)0.0373 (8)0.0326 (8)−0.0182 (6)0.0064 (6)−0.0048 (6)
C20.0292 (7)0.0262 (7)0.0282 (7)−0.0087 (5)−0.0004 (5)−0.0026 (5)
C30.0335 (7)0.0356 (8)0.0233 (6)−0.0095 (6)0.0045 (5)−0.0072 (6)
C40.0337 (7)0.0255 (7)0.0271 (7)−0.0079 (5)0.0007 (5)−0.0094 (5)
C50.0245 (6)0.0211 (6)0.0257 (6)−0.0057 (5)0.0005 (5)−0.0032 (5)
C60.0342 (7)0.0254 (7)0.0291 (7)−0.0087 (5)0.0073 (5)−0.0095 (6)
C70.0352 (7)0.0235 (7)0.0346 (7)−0.0101 (5)0.0047 (6)−0.0094 (6)
C80.0309 (7)0.0215 (7)0.0301 (7)−0.0083 (5)−0.0009 (5)−0.0080 (5)
C90.0275 (6)0.0230 (7)0.0328 (7)−0.0086 (5)−0.0023 (5)−0.0051 (6)
Geometric parameters (Å, º) top
O1—C11.2196 (18)C5—C61.3969 (18)
O2—C51.3593 (15)C6—C71.3704 (18)
O2—C81.4372 (15)C6—H60.9500
C1—C21.4652 (18)C7—H70.9500
C1—H10.9500C8—C91.5105 (17)
C2—C31.3857 (19)C8—H8A0.9900
C2—C71.396 (2)C8—H8B0.9900
C3—C41.3871 (18)C9—C9i1.525 (3)
C3—H30.9500C9—H9A0.9900
C4—C51.3933 (18)C9—H9B0.9900
C4—H40.9500
C5—O2—C8118.23 (10)C7—C6—H6120.1
O1—C1—C2124.62 (14)C5—C6—H6120.1
O1—C1—H1117.7C6—C7—C2120.93 (13)
C2—C1—H1117.7C6—C7—H7119.5
C3—C2—C7118.64 (12)C2—C7—H7119.5
C3—C2—C1120.77 (13)O2—C8—C9107.25 (10)
C7—C2—C1120.58 (13)O2—C8—H8A110.3
C2—C3—C4121.52 (12)C9—C8—H8A110.3
C2—C3—H3119.2O2—C8—H8B110.3
C4—C3—H3119.2C9—C8—H8B110.3
C3—C4—C5118.82 (12)H8A—C8—H8B108.5
C3—C4—H4120.6C8—C9—C9i113.78 (13)
C5—C4—H4120.6C8—C9—H9A108.8
O2—C5—C4124.74 (12)C9i—C9—H9A108.8
O2—C5—C6115.04 (11)C8—C9—H9B108.8
C4—C5—C6120.22 (12)C9i—C9—H9B108.8
C7—C6—C5119.85 (12)H9A—C9—H9B107.7
O1—C1—C2—C3−175.28 (14)C3—C4—C5—C61.0 (2)
O1—C1—C2—C74.3 (2)O2—C5—C6—C7179.96 (11)
C7—C2—C3—C4−1.3 (2)C4—C5—C6—C7−1.0 (2)
C1—C2—C3—C4178.22 (12)C5—C6—C7—C2−0.2 (2)
C2—C3—C4—C50.2 (2)C3—C2—C7—C61.4 (2)
C8—O2—C5—C45.11 (18)C1—C2—C7—C6−178.21 (12)
C8—O2—C5—C6−175.90 (10)C5—O2—C8—C9179.31 (10)
C3—C4—C5—O2179.95 (11)O2—C8—C9—C9i64.84 (16)
Symmetry code: (i) −x+2, −y+1, −z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C6—H6···O2ii0.952.583.4985 (16)162
C1—H1···O1iii0.952.593.3953 (18)143
Symmetry codes: (ii) −x+2, −y, −z+1; (iii) −x, −y−1, −z+2.

Experimental details

Crystal data
Chemical formulaC18H18O4
Mr298.32
Crystal system, space groupTriclinic, P1
Temperature (K)190
a, b, c (Å)4.4969 (2), 7.9507 (6), 11.0679 (8)
α, β, γ (°)73.854 (6), 84.788 (5), 80.903 (5)
V (Å3)374.86 (4)
Z1
Radiation typeMo Kα
µ (mm−1)0.09
Crystal size (mm)0.59 × 0.35 × 0.21
Data collection
DiffractometerOxford Diffraction Xcalibur Sapphire3
Absorption correctionMulti-scan
(CrysAlis PRO; Oxford Diffraction, 2009)
Tmin, Tmax0.683, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections		2235, 1473, 1272
Rint0.010
(sin θ/λ)max (Å−1)0.616
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.043, 0.123, 1.04
No. of reflections1473
No. of parameters100
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å−3)0.29, −0.17

Computer programs: CrysAlis PRO (Oxford Diffraction, 2009), SIR2004 (Burla et al., 2005), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 2012), WinGX (Farrugia, 2012), PARST97 (Nardelli, 1995) and Mercury (Macrae et al., 2006).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C6—H6···O2i0.952.583.4985 (16)161.9
C1—H1···O1ii0.952.593.3953 (18)143.0
Symmetry codes: (i) −x+2, −y, −z+1; (ii) −x, −y−1, −z+2.
 

Acknowledgements

This work was supported by the Ministry of Science, Education and Sports of the Republic of Croatia (grant No. 119–1193079-1084). The authors wish to thank Professor Dubravka Matković-Čalogović for help with the crystallography.

References

First citationBalić, T., Marković, B. & Balić, I. (2012). Acta Cryst. E68, o2664.  CSD CrossRef IUCr Journals Google Scholar
 First citationBernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555–1573.  CrossRef CAS Web of Science Google Scholar
 First citationBurla, M. C., Caliandro, R., Camalli, M., Carrozzini, B., Cascarano, G. L., De Caro, L., Giacovazzo, C., Polidori, G. & Spagna, R. (2005). J. Appl. Cryst. 38, 381–388.  Web of Science CrossRef CAS IUCr Journals Google Scholar
 First citationDehno Khalaji, A., Hafez Ghoran, S., Gotoh, K. & Ishida, H. (2011). Acta Cryst. E67, o2484.  Web of Science CSD CrossRef IUCr Journals Google Scholar
 First citationFarrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854.  Web of Science CrossRef CAS IUCr Journals Google Scholar
 First citationHan, J.-R. & Zhen, X.-L. (2005). Acta Cryst. E61, o4358–o4359.  Web of Science CSD CrossRef IUCr Journals Google Scholar
 First citationIlhan, S., Temel, H., Yilmaz, I. & Kilic, A. (2007). Transition Met. Chem. 32, 344–349.  Web of Science CrossRef CAS Google Scholar
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ISSN: 2056-9890
Volume 69| Part 1| January 2013| Page o126
https://doi.org/10.1107/S1600536812050994
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