Bis[eth­yl(2-hydroxy­ethyl)aza­nium] 2,2′-disulfanediyldibenzoate

Broker, G.A.; Tiekink, E.R.T.

doi:10.1107/S1600536810006781

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 66| Part 3| March 2010| Page o705

doi:10.1107/S1600536810006781

Open

access

Bis[ethyl(2-hydroxyethyl)azanium] 2,2′-disulfanediyldibenzoate

Grant A. Broker ^a and Edward R. T. Tiekink ^b ^*

^a5959 FM 1960 Road West, Houston, Texas 77069, USA, and ^bDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
^*Correspondence e-mail: edward.tiekink@gmail.com

(Received 18 February 2010; accepted 22 February 2010; online 27 February 2010)

The asymmetric unit of the title salt, 2C₄H₁₂NO⁺·C₁₄H₈O₄S₂²⁻, contains an ethyl(2-hydroxy)aminium cation and half a 2,2′-disulfanediyldibenzoate anion, with the latter disposed about a twofold axis. The cation is a straight chain with the exception of the terminal hydroxy group [the N—C—C—O torsion angle is 66.5 (2)°]. A twisted conformation is found for the anion [the C—S—S—C torsion angle is 91.51 (9)° and the dihedral angle between the rings is 81.01 (4)°]. A supramolecular chain with base vector [101] and a tubular topology is formed in the crystal structure mediated by charge-assisted O—H⋯O⁻ and N⁺—H⋯O⁻ hydrogen bonding.

Related literature

For related studies on co-crystal/salt formation involving 2-[(2-carboxyphenyl)disulfanyl]benzoic acid, see: Broker & Tiekink (2007 ); Broker et al. (2008 ). For software used to search the Cambridge Structural Database, see: Bruno et al. (2002 ).

Experimental

Crystal data

2C₄H₁₂NO⁺·C₁₄H₈O₄S₂²⁻
M_r = 484.64
Monoclinic, C 2/c
a = 22.949 (5) Å
b = 8.2429 (16) Å
c = 14.766 (3) Å
β = 119.80 (3)°
V = 2423.9 (11) Å³
Z = 4
Mo Kα radiation
μ = 0.26 mm⁻¹
T = 173 K
0.40 × 0.25 × 0.10 mm

Data collection

Rigaku AFC12/SATURN724 CCD-detector diffractometer
Absorption correction: multi-scan (ABSCOR; Higashi, 1995 ) T_min = 0.800, T_max = 1.000
7823 measured reflections
2503 independent reflections
2367 reflections with I > 2σ(I)
R_int = 0.032

Refinement

R[F² > 2σ(F²)] = 0.039
wR(F²) = 0.100
S = 1.14
2503 reflections
148 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.34 e Å⁻³
Δρ_min = −0.22 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯O1ⁱ	0.92	1.94	2.840 (2)	164
N1—H1B⋯O2	0.92	1.85	2.7617 (19)	171
O3—H3⋯O2ⁱ	0.84	1.92	2.763 (2)	177
Symmetry code: (i) $[-x+{\script{1\over 2}}, -y+{\script{3\over 2}}, -z+1]$ .

Data collection: CrystalClear (Rigaku/MSC, 2005 ); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPII (Johnson, 1976 ) and DIAMOND (Brandenburg, 2006 ); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810006781/zs2030sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536810006781/zs2030Isup2.hkl

checkCIF report

Comment top

The title salt, (I), was obtained during crystallisation experiments involving 2-[(2-carboxyphenyl)disulfanyl]benzoic acid with various N-containing species (Broker & Tiekink, 2007; Broker et al., 2008). The asymmetric unit comprises an aminium cation (Fig. 1) and half a dithiodibenzoate anion (Fig. 2), with the latter disposed about a crystallographic 2-fold axis. The cation is linear with the exception of the terminal hydroxy group which is twisted out of the chain as seen in the O3–C8–C9–N1 torsion angle [66.5 (2)°]. Confirmation of protonation of the amine-N1 atom during crystallisation is seen in the pattern of hydrogen-bonding interactions (see below). A search of the CSD (Bruno et al., 2002) suggests that this is the first structural characterisation reported for the ethyl(2-hydroxyethyl)aminium cation. The dithiodibenzoate anion is twisted [torsion angle C3–S1–S1ⁱ–C3ⁱ = 91.51 (9)°: for symmetry code i, -x, y, 1/2-z] in accord with expectation, with the conformation stabilised by an intramolecular S···O interaction of 2.7351 (16) Å (Broker & Tiekink (2007). The carboxylate group is twisted out of the plane of the benzene ring to which it is connected with the C3–C2–C1–O1 torsion angle being -25.0 (2) °. Confirmation of deprotonation of the carboxylic acid is consistent with the observed near equivalence of the C1–O1 and C1–O2 bond distances [1.2499 (19) and 1.270 (2) Å] with the weaker C1–O2 bond correlated to the participation of the O2 atom in two hydrogen bonding interactions compared to one for the O1 atom. The crystal packing is dominated by charge-assisted O–H···O^- and N⁺–H···O^- hydrogen bonding (Table 1). Each of the aminium-H atoms connects to a carboxylate-O atom and the O2 atom is also hydrogen-bonded to the hydroxy group. The result of these interactions is a supramolecular chain with base vector [1 0 1] (Fig. 3), which has a tubular topology (Fig. 4).

Related literature top

For related studies on co-crystal/salt formation involving 2-[(2-carboxyphenyl)disulfanyl]benzoic acid, see: Broker & Tiekink (2007); Broker et al. (2008). For software used to search the Cambridge Structural Database, see: Bruno et al. (2002).

Experimental top

The title salt (I) was obtained by dissolving 2-[(2-carboxyphenyl)disulfanyl]benzoic acid (0.100 g, Fluka) in ethanol (20 ml) to which was added the amine in 1:1, 1:2 and 1:3 stoichiometric ratios in three separate experiments. Regardless of the stoichiometry, only crystals of (I) were harvested as proved by multiple unit cell determinations, m.p. 429–431 K

Computing details top

Data collection: CrystalClear (Rigaku/MSC, 2005); cell refinement: CrystalClear (Rigaku/MSC, 2005); data reduction: CrystalClear (Rigaku/MSC, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPII (Johnson, 1976) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

	Fig. 1. Molecular structure of the cation in (I) showing atom-labelling scheme and displacement ellipsoids at the 50% probability level.
	Fig. 2. Molecular structure of the anion in (I) showing atom-labelling scheme and displacement ellipsoids at the 50% probability level. The anion has crystallographic 2-fold symmetry; i: -x, y, 1/2-z.
	Fig. 3. Supramolecular chain formation in (I) mediated by charge-assisted O–H···O^- (orange dashed lines) and N⁺–H···O^- (blue dashed lines) hydrogen bonding. Colour code: S, yellow; O, red; N, blue; C, grey; H, green.
	Fig. 4. An end-on view of the supramolecular chain shown in Fig. 3 highlighting the tubular topology. The charge-assisted O–H···O^- and N⁺–H···O^- hydrogen-bonding interactions are indicated by orange and blue dashed lines, respectively. Colour code: S, yellow; O, red; N, blue; C, grey; H, green.

Ethyl(2-hydroxyethyl)azanium 2,2'-disulfanediyldibenzoate top

Crystal data top

2C₄H₁₂NO⁺·C₁₄H₈O₄S₂²⁻	F(000) = 1032
M_r = 484.64	D_x = 1.328 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 5747 reflections
a = 22.949 (5) Å	θ = 3.6–30.5°
b = 8.2429 (16) Å	µ = 0.26 mm⁻¹
c = 14.766 (3) Å	T = 173 K
β = 119.80 (3)°	Block, colourless
V = 2423.9 (11) Å³	0.40 × 0.25 × 0.10 mm
Z = 4

Data collection top

Rigaku AFC12K/SATURN724 CCD-detector diffractometer	2503 independent reflections
Radiation source: fine-focus sealed tube	2367 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.032
ω scans	θ_max = 26.5°, θ_min = 3.6°
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	h = −28→25
T_min = 0.800, T_max = 1.000	k = −10→10
7823 measured reflections	l = −18→18

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.100	H-atom parameters constrained
S = 1.14	w = 1/[σ²(F_o²) + (0.0437P)² + 1.6814P] where P = (F_o² + 2F_c²)/3
2503 reflections	(Δ/σ)_max = 0.001
148 parameters	Δρ_max = 0.34 e Å⁻³
1 restraint	Δρ_min = −0.22 e Å⁻³

Crystal data top

2C₄H₁₂NO⁺·C₁₄H₈O₄S₂²⁻	V = 2423.9 (11) Å³
M_r = 484.64	Z = 4
Monoclinic, C2/c	Mo Kα radiation
a = 22.949 (5) Å	µ = 0.26 mm⁻¹
b = 8.2429 (16) Å	T = 173 K
c = 14.766 (3) Å	0.40 × 0.25 × 0.10 mm
β = 119.80 (3)°

Data collection top

Rigaku AFC12K/SATURN724 CCD-detector diffractometer	2503 independent reflections
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	2367 reflections with I > 2σ(I)
T_min = 0.800, T_max = 1.000	R_int = 0.032
7823 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.039	1 restraint
wR(F²) = 0.100	H-atom parameters constrained
S = 1.14	Δρ_max = 0.34 e Å⁻³
2503 reflections	Δρ_min = −0.22 e Å⁻³
148 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 > 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
S1	0.04587 (2)	0.42885 (5)	0.31713 (3)	0.02621 (14)
O1	0.17238 (6)	0.44668 (13)	0.48609 (9)	0.0272 (3)
O2	0.21265 (6)	0.67861 (14)	0.57133 (9)	0.0269 (3)
O3	0.17235 (7)	0.9908 (2)	0.29494 (10)	0.0453 (4)
H3	0.2072	0.9376	0.3338	0.068*
N1	0.20710 (7)	1.00243 (16)	0.51963 (10)	0.0231 (3)
H1A	0.2410	1.0242	0.5052	0.028*
H1B	0.2069	0.8923	0.5296	0.028*
C1	0.16465 (8)	0.58217 (18)	0.51667 (12)	0.0223 (3)
C2	0.09497 (8)	0.63551 (18)	0.48785 (12)	0.0222 (3)
C3	0.03728 (8)	0.57605 (18)	0.39935 (12)	0.0236 (3)
C4	−0.02554 (9)	0.6307 (2)	0.37906 (14)	0.0329 (4)
H4	−0.0647	0.5931	0.3187	0.039*
C5	−0.03181 (10)	0.7382 (2)	0.44505 (15)	0.0376 (4)
H5	−0.0752	0.7728	0.4303	0.045*
C6	0.02468 (9)	0.7965 (2)	0.53293 (14)	0.0335 (4)
H6	0.0203	0.8701	0.5787	0.040*
C7	0.08727 (9)	0.74627 (19)	0.55301 (13)	0.0269 (4)
H7	0.1261	0.7877	0.6124	0.032*
C8	0.12733 (9)	0.9551 (2)	0.33125 (14)	0.0351 (4)
H8A	0.1298	0.8376	0.3468	0.042*
H8B	0.0810	0.9794	0.2753	0.042*
C9	0.14185 (9)	1.0497 (2)	0.42769 (13)	0.0306 (4)
H9A	0.1427	1.1670	0.4139	0.037*
H9B	0.1053	1.0309	0.4437	0.037*
C10	0.22223 (9)	1.0870 (2)	0.61827 (14)	0.0316 (4)
H10A	0.1855	1.0671	0.6336	0.038*
H10B	0.2252	1.2053	0.6099	0.038*
C11	0.28740 (10)	1.0267 (3)	0.70735 (15)	0.0430 (5)
H11A	0.2967	1.0832	0.7716	0.065*
H11B	0.3238	1.0477	0.6924	0.065*
H11C	0.2842	0.9098	0.7162	0.065*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S1	0.0231 (2)	0.0274 (2)	0.0238 (2)	0.00348 (15)	0.00832 (17)	−0.00108 (15)
O1	0.0244 (6)	0.0241 (6)	0.0319 (6)	0.0018 (5)	0.0131 (5)	−0.0030 (5)
O2	0.0229 (6)	0.0252 (6)	0.0285 (6)	−0.0020 (5)	0.0097 (5)	−0.0005 (5)
O3	0.0373 (8)	0.0698 (10)	0.0298 (7)	0.0153 (7)	0.0174 (6)	0.0157 (7)
N1	0.0237 (7)	0.0218 (7)	0.0246 (7)	0.0019 (5)	0.0126 (6)	0.0006 (5)
C1	0.0239 (8)	0.0234 (8)	0.0194 (7)	0.0006 (6)	0.0107 (7)	0.0047 (6)
C2	0.0239 (8)	0.0194 (7)	0.0243 (8)	0.0022 (6)	0.0128 (7)	0.0051 (6)
C3	0.0234 (8)	0.0231 (8)	0.0243 (8)	0.0029 (6)	0.0118 (7)	0.0039 (6)
C4	0.0237 (9)	0.0377 (10)	0.0326 (9)	0.0040 (8)	0.0105 (8)	−0.0010 (8)
C5	0.0288 (10)	0.0427 (10)	0.0431 (10)	0.0101 (8)	0.0192 (9)	−0.0002 (9)
C6	0.0386 (10)	0.0316 (9)	0.0370 (9)	0.0056 (8)	0.0239 (8)	−0.0013 (8)
C7	0.0307 (9)	0.0239 (8)	0.0261 (8)	−0.0002 (7)	0.0142 (7)	0.0004 (7)
C8	0.0273 (9)	0.0471 (10)	0.0247 (9)	0.0033 (8)	0.0083 (7)	0.0042 (8)
C9	0.0256 (9)	0.0318 (9)	0.0311 (9)	0.0069 (7)	0.0117 (8)	0.0062 (7)
C10	0.0373 (10)	0.0296 (9)	0.0323 (9)	−0.0014 (7)	0.0207 (8)	−0.0073 (7)
C11	0.0356 (11)	0.0634 (13)	0.0266 (9)	−0.0058 (10)	0.0128 (8)	−0.0115 (9)

Geometric parameters (Å, º) top

S1—C3	1.7953 (16)	C5—C6	1.387 (3)
S1—S1ⁱ	2.0528 (13)	C5—H5	0.9500
O1—C1	1.2499 (19)	C6—C7	1.378 (2)
O2—C1	1.270 (2)	C6—H6	0.9500
O3—C8	1.411 (2)	C7—H7	0.9500
O3—H3	0.8401	C8—C9	1.509 (3)
N1—C9	1.489 (2)	C8—H8A	0.9900
N1—C10	1.492 (2)	C8—H8B	0.9900
N1—H1A	0.9200	C9—H9A	0.9900
N1—H1B	0.9200	C9—H9B	0.9900
C1—C2	1.502 (2)	C10—C11	1.503 (3)
C2—C7	1.400 (2)	C10—H10A	0.9900
C2—C3	1.407 (2)	C10—H10B	0.9900
C3—C4	1.393 (2)	C11—H11A	0.9800
C4—C5	1.377 (3)	C11—H11B	0.9800
C4—H4	0.9500	C11—H11C	0.9800

C3—S1—S1ⁱ	104.39 (6)	C6—C7—H7	119.3
C8—O3—H3	105.1	C2—C7—H7	119.3
C9—N1—C10	114.12 (13)	O3—C8—C9	113.00 (16)
C9—N1—H1A	108.7	O3—C8—H8A	109.0
C10—N1—H1A	108.7	C9—C8—H8A	109.0
C9—N1—H1B	108.7	O3—C8—H8B	109.0
C10—N1—H1B	108.7	C9—C8—H8B	109.0
H1A—N1—H1B	107.6	H8A—C8—H8B	107.8
O1—C1—O2	123.69 (15)	N1—C9—C8	112.07 (14)
O1—C1—C2	118.79 (14)	N1—C9—H9A	109.2
O2—C1—C2	117.52 (14)	C8—C9—H9A	109.2
C7—C2—C3	118.91 (15)	N1—C9—H9B	109.2
C7—C2—C1	118.46 (14)	C8—C9—H9B	109.2
C3—C2—C1	122.62 (14)	H9A—C9—H9B	107.9
C4—C3—C2	118.84 (15)	N1—C10—C11	110.34 (14)
C4—C3—S1	121.51 (13)	N1—C10—H10A	109.6
C2—C3—S1	119.63 (12)	C11—C10—H10A	109.6
C5—C4—C3	121.12 (17)	N1—C10—H10B	109.6
C5—C4—H4	119.4	C11—C10—H10B	109.6
C3—C4—H4	119.4	H10A—C10—H10B	108.1
C4—C5—C6	120.48 (17)	C10—C11—H11A	109.5
C4—C5—H5	119.8	C10—C11—H11B	109.5
C6—C5—H5	119.8	H11A—C11—H11B	109.5
C7—C6—C5	119.15 (16)	C10—C11—H11C	109.5
C7—C6—H6	120.4	H11A—C11—H11C	109.5
C5—C6—H6	120.4	H11B—C11—H11C	109.5
C6—C7—C2	121.48 (16)

O1—C1—C2—C7	153.69 (15)	C2—C3—C4—C5	−1.4 (3)
O2—C1—C2—C7	−26.3 (2)	S1—C3—C4—C5	177.14 (15)
O1—C1—C2—C3	−25.0 (2)	C3—C4—C5—C6	0.9 (3)
O2—C1—C2—C3	155.09 (14)	C4—C5—C6—C7	0.5 (3)
C7—C2—C3—C4	0.6 (2)	C5—C6—C7—C2	−1.3 (3)
C1—C2—C3—C4	179.26 (15)	C3—C2—C7—C6	0.7 (2)
C7—C2—C3—S1	−177.96 (12)	C1—C2—C7—C6	−177.99 (15)
C1—C2—C3—S1	0.7 (2)	C10—N1—C9—C8	−177.21 (14)
S1ⁱ—S1—C3—C4	16.34 (15)	O3—C8—C9—N1	−66.5 (2)
S1ⁱ—S1—C3—C2	−165.14 (11)	C9—N1—C10—C11	177.61 (15)

Symmetry code: (i) −x, y, −z+1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1ⁱⁱ	0.92	1.94	2.840 (2)	164
N1—H1B···O2	0.92	1.85	2.7617 (19)	171
O3—H3···O2ⁱⁱ	0.84	1.92	2.763 (2)	177

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

Experimental details

Crystal data
Chemical formula	2C₄H₁₂NO⁺·C₁₄H₈O₄S₂²⁻
M_r	484.64
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	173
a, b, c (Å)	22.949 (5), 8.2429 (16), 14.766 (3)
β (°)	119.80 (3)
V (Å³)	2423.9 (11)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.26
Crystal size (mm)	0.40 × 0.25 × 0.10

Data collection
Diffractometer	Rigaku AFC12K/SATURN724 CCD-detector diffractometer
Absorption correction	Multi-scan (ABSCOR; Higashi, 1995)
T_min, T_max	0.800, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	7823, 2503, 2367
R_int	0.032
(sin θ/λ)_max (Å⁻¹)	0.628

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.039, 0.100, 1.14
No. of reflections	2503
No. of parameters	148
No. of restraints	1
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.34, −0.22

Computer programs: CrystalClear (Rigaku/MSC, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEPII (Johnson, 1976) and DIAMOND (Brandenburg, 2006), publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1ⁱ	0.92	1.94	2.840 (2)	164
N1—H1B···O2	0.92	1.85	2.7617 (19)	171
O3—H3···O2ⁱ	0.84	1.92	2.763 (2)	177

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

References

Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany. Google Scholar
Broker, G. A., Bettens, R. P. A. & Tiekink, E. R. T. (2008). CrystEngComm, 10, 879–887. Web of Science CSD CrossRef CAS Google Scholar
Broker, G. A. & Tiekink, E. R. T. (2007). CrystEngComm, 9, 1096–1109. Web of Science CSD CrossRef CAS Google Scholar
Bruno, I. J., Cole, J. C., Edgington, P. R., Kessler, M., Macrae, C. F., McCabe, P., Pearson, J. & Taylor, R. (2002). Acta Cryst. B58, 389–397. Web of Science CrossRef CAS IUCr Journals Google Scholar
Higashi, T. (1995). ABSCOR. Rigaku Corporation, Tokyo, Japan. Google Scholar
Johnson, C. K. (1976). ORTEPII. Report ORNL-5138. Oak Ridge National Laboratory, Tennessee, USA. Google Scholar
Rigaku/MSC (2005). CrystalClear. Rigaku/MSC Inc., The Woodlands, Texas, USA. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Westrip, S. P. (2010). publCIF. In preparation. 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 66| Part 3| March 2010| Page o705

doi:10.1107/S1600536810006781

Open

access