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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 67| Part 9| September 2011| Page o2290
doi:10.1107/S1600536811031540

Caffeinium bis­­ulfate monohydrate

C. Vincent Jerina and S. Athimoolama*

aDepartment of Physics, University College of Engineering Nagercoil, Anna University of Technology Tirunelveli, Nagercoil 629 004, India
*Correspondence e-mail: athi81s@yahoo.co.in

(Received 2 August 2011; accepted 4 August 2011; online 11 August 2011)

In the title compound (systematic name: 1,3,7-trimethyl-2,6-dioxo-7H-purin-9-ium hydrogen sulfate monohydrate), C8H11N4O2+·HSO4−·H2O, the crystal packing is stabilized through N—H⋯O and O—H⋯O hydrogen bonds.

Related literature

For background to caffeine, see: Benowitz (1990[Benowitz, N. L. (1990). Annu. Rev. Med. 41, 277-288.]); Smith (2002[Smith, A. (2002). Food Chem. Toxicol. 40, 9, 1243-1255.]); Griesser & Burger (1995[Griesser, U. J. & Burger, A. (1995). Int. J. Pharm. 120, 83-93.]); Bothe & Cammenga (1980[Bothe, H. & Cammenga, H. K. (1980). Thermochim. Acta, 40, 29-39.]); Edwards et al. (1997[Edwards, H. G. M., Lawson, E., de Matas, M., Shields, L. & York, P. (1997). J. Chem. Soc. Perkin Trans. 2, pp. 1985-1990.]); Sutor (1958[Sutor, D. J. (1958). Acta Cryst. 11, 453-458.]); Trask et al. (2005[Trask, A. V., Motherwell, W. D. S. & Jones, W. (2005). Cryst. Growth Des. 5, 1013-1021.]). For hydrogen-bond motifs, see: Etter et al. (1990[Etter, M. C., MacDonald, J. C. & Bernstein, J. (1990). Acta Cryst. B46, 256-262.]).

[Scheme 1]

Experimental

Crystal data

  • C8H11N4O2+·HSO4−·H2O

  • Mr = 310.29

  • Monoclinic, P 21 /c

  • a = 9.8296 (10) Å

  • b = 6.2879 (6) Å

  • c = 21.340 (2) Å

  • β = 90.788 (2)°

  • V = 1318.8 (2) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.29 mm−1

  • T = 293 K

  • 0.21 × 0.18 × 0.13 mm
Data collection

  • Bruker SMART APEX CCD area-detector diffractometer

  • 11981 measured reflections

  • 2317 independent reflections

  • 2200 reflections with I > 2σ(I)

  • Rint = 0.020
Refinement

  • R[F2 > 2σ(F2)] = 0.039

  • wR(F2) = 0.111

  • S = 1.08

  • 2317 reflections

  • 201 parameters

  • 3 restraints

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

  • Δρmax = 0.43 e Å−3

  • Δρmin = −0.38 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A D⋯A D—H⋯A
N1—H1N⋯O13i 0.88 (2) 1.83 (2) 2.709 (2) 174 (2)
O14—H14⋯O1Wii 0.88 (3) 1.60 (4) 2.479 (3) 171 (3)
O1W—H1W⋯O13iii 0.94 (1) 1.82 (1) 2.742 (2) 168 (4)
O1W—H2W⋯O11 0.94 (1) 1.98 (3) 2.711 (2) 133 (3)
Symmetry codes: (i) -x+1, -y+1, -z+2; (ii) -x, -y+2, -z+2; (iii) -x, -y+1, -z+2.

Data collection: SMART (Bruker, 2001[Bruker (2001). SAINT and SMART . Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2001[Bruker (2001). SAINT and SMART . Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXTL/PC (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXTL/PC; molecular graphics: PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]); software used to prepare material for publication: SHELXTL/PC.

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811031540/bt5603sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811031540/bt5603Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536811031540/bt5603Isup3.cml

checkCIF report


Comment top

Caffeine is an alkaloid and structurally identified as 1,3,7-trimethylxanthine. It is one of several xanthine derivatives which occur naturally in cofee beans, tea leaves, kola nuts and cocoa beans. It is the most widely consumed stimulant drug in the world (Benowitz, 1990). Caffeine is a central nervous system stimulant and a smooth muscle relaxant, and is commonly employed as a formulation additive to analgesic remedies. Moderate consumption of caffeine increases alertness and reduces fatigues (Smith, 2002). Apart from the above, caffeine is a model pharmaceutical compound that is known to exhibit instability with respect to humidity, with the formation of a crystalline nonstoichiometric hydrate (Griesser & Burger, 1995). Its solid-state properties have been widely investigated; it is known to occur in two anhydrous crystal froms (α, β), one crystalline nonstoichiometric hydrate (Bothe & Cammenga, 1980) and a number of simple cocrystals and salts (Trask et al., 2005). The crystal structure of the hydrated form was determined a long time ago (Sutor, 1958) and confirmed recently (Edwards et al., 1997). In the present work, caffeine was treated with sulfuric acid and the structure of the title compound, (I), is reported here.

The asymmetric part of (I) contains a caffeinium cation, bisulfate anion and a lattice water molecule (Fig. 1). The protonation on the N site of the cation is confirmed from C—N bond distances and C—N—C bond angle. The presence of H atom in one of the O atoms of the bisulfate anion is confirmed from the asymmetric S—O bond distances. This ascertain the bisulfate nature of the anion. The crystal packing is stabilized through N–H···O and O–H···O hydrogen bonds (Table 1; Fig. 2). Anions are dimerized themselves through lattice water molecule and making two adjacent ring R44(12) motifs around the inversion centeres of the unit cell (Etter et al., 1990). Further, cations are linked to this anionic dimers through another N–H···O hydrogen bond.

Related literature top

For background to caffeine, see: Benowitz (1990); Smith (2002); Griesser & Burger (1995); Bothe & Cammenga (1980); Edwards et al. (1997); Sutor (1958); Trask et al. (2005). For hydrogen-bond motifs, see: Etter et al. (1990).

Experimental top

The title compound was crystallized from an aqueous mixture containing caffeine and sulfuric acid in the stoichiometric ratio of 1:1 at room temperature by slow evaporation technique.

Refinement top

All the H atoms, except the H atoms involved in the hydrogen bonds, were positioned geometrically and refined by the riding model approximation with d(C—H) = 0.93 Å and Uiso(H)= 1.2 Ueq(C) for aromatic H and d(C—H) = 0.96 Å and Uiso(H)= 1.5 Ueq(C) for methyl H. The H atoms of the –NH group of the cation and water molecule were located from difference fourier map and refined isotropically. The O-H distances of the water molecule are restrained to 0.95 (1)Å and the H···H distance to 1.64 (10)Å.

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXTL/PC (Sheldrick, 2008); program(s) used to refine structure: SHELXTL/PC (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXTL/PC (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound with atom numbering scheme and 50% probability displacement ellipsoids. H-bonds are shown as dashed lines.
[Figure 2] Fig. 2. Packing diagram of the title compound viewed down the b-axis. H-bonds are shown as dashed lines.
1,3,7-trimethyl-2,6-dioxo-7H-purin-9-ium hydrogen sulfate monohydrate top
Crystal data top
C8H11N4O2+·HSO4−·H2OF(000) = 648
Mr = 310.29Dx = 1.563 Mg m−3
Dm = 1.55 (1) Mg m−3
Dm measured by flotation technique using a liquid-mixture of xylene and bromoform
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 2986 reflections
a = 9.8296 (10) Åθ = 2.1–24.4°
b = 6.2879 (6) ŵ = 0.29 mm−1
c = 21.340 (2) ÅT = 293 K
β = 90.788 (2)°Block, colourless
V = 1318.8 (2) Å30.21 × 0.18 × 0.13 mm
Z = 4
Data collection top
Bruker SMART APEX CCD area-detector
diffractometer		2200 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.020
Graphite monochromatorθmax = 25.0°, θmin = 1.9°
ω scansh = −11→11
11981 measured reflectionsk = −7→7
2317 independent reflectionsl = −25→25
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) = 0.111 w = 1/[σ2(Fo2) + (0.0659P)2 + 0.5199P]
where P = (Fo2 + 2Fc2)/3
S = 1.08(Δ/σ)max = 0.001
2317 reflectionsΔρmax = 0.43 e Å−3
201 parametersΔρmin = −0.38 e Å−3
3 restraintsExtinction correction: SHELXTL/PC (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.030 (3)
Crystal data top
C8H11N4O2+·HSO4−·H2OV = 1318.8 (2) Å3
Mr = 310.29Z = 4
Monoclinic, P21/cMo Kα radiation
a = 9.8296 (10) ŵ = 0.29 mm−1
b = 6.2879 (6) ÅT = 293 K
c = 21.340 (2) Å0.21 × 0.18 × 0.13 mm
β = 90.788 (2)°
Data collection top
Bruker SMART APEX CCD area-detector
diffractometer		2200 reflections with I > 2σ(I)
11981 measured reflectionsRint = 0.020
2317 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0393 restraints
wR(F2) = 0.111H atoms treated by a mixture of independent and constrained refinement
S = 1.08Δρmax = 0.43 e Å−3
2317 reflectionsΔρmin = −0.38 e Å−3
201 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
C10.36935 (19)0.2793 (3)0.91192 (9)0.0440 (4)
H10.37940.17020.94100.053*
C20.28869 (17)0.4803 (3)0.83632 (8)0.0400 (4)
C30.21533 (19)0.5681 (3)0.78425 (9)0.0462 (5)
C40.39035 (19)0.8556 (3)0.78816 (8)0.0429 (4)
C50.2076 (2)0.8651 (4)0.71053 (11)0.0653 (6)
H5A0.19931.01440.71910.098*
H5B0.11870.80540.70350.098*
H5C0.26160.84480.67390.098*
C60.5833 (2)0.8438 (3)0.86283 (10)0.0516 (5)
H6A0.58260.83890.90780.077*
H6B0.59270.98860.84930.077*
H6C0.65830.76140.84780.077*
C70.40523 (17)0.5697 (3)0.85864 (8)0.0373 (4)
C80.1474 (2)0.1599 (4)0.86777 (11)0.0580 (5)
H8A0.16700.02710.88820.087*
H8B0.12340.13420.82470.087*
H8C0.07290.22830.88830.087*
N10.45565 (16)0.4425 (2)0.90488 (7)0.0417 (4)
N20.26785 (15)0.2975 (2)0.87113 (7)0.0418 (4)
N30.27344 (16)0.7589 (3)0.76434 (7)0.0444 (4)
N40.45593 (15)0.7565 (2)0.83794 (7)0.0395 (4)
O30.11562 (16)0.4920 (3)0.75848 (8)0.0699 (5)
O40.43242 (15)1.0219 (2)0.76720 (7)0.0582 (4)
H1N0.533 (2)0.454 (4)0.9257 (10)0.051 (6)*
S10.25373 (4)0.72796 (7)1.01018 (2)0.0398 (2)
O110.16152 (15)0.6931 (3)0.95835 (7)0.0600 (4)
O120.36818 (15)0.8565 (2)0.99415 (8)0.0623 (4)
O130.29697 (14)0.5271 (2)1.03835 (7)0.0521 (4)
O140.17650 (16)0.8381 (3)1.06289 (7)0.0580 (4)
H140.152 (3)0.966 (6)1.0503 (14)0.092 (10)*
O1W−0.10677 (19)0.7918 (3)0.96137 (17)0.1136 (10)
H1W−0.162 (3)0.670 (4)0.9608 (17)0.130 (13)*
H2W−0.035 (3)0.729 (6)0.9394 (17)0.139 (16)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0478 (10)0.0389 (10)0.0454 (10)0.0031 (8)0.0057 (8)0.0045 (8)
C20.0389 (9)0.0416 (10)0.0397 (9)−0.0008 (7)0.0042 (7)0.0005 (7)
C30.0414 (10)0.0537 (11)0.0435 (10)−0.0022 (8)0.0015 (8)0.0016 (8)
C40.0453 (10)0.0436 (10)0.0401 (9)0.0030 (8)0.0079 (7)0.0026 (8)
C50.0641 (13)0.0766 (16)0.0550 (12)0.0001 (12)−0.0103 (10)0.0224 (12)
C60.0469 (10)0.0471 (11)0.0606 (12)−0.0079 (9)−0.0030 (9)0.0005 (9)
C70.0384 (9)0.0370 (9)0.0367 (8)0.0023 (7)0.0052 (7)−0.0009 (7)
C80.0530 (12)0.0536 (12)0.0675 (13)−0.0146 (10)0.0047 (10)0.0054 (10)
N10.0404 (8)0.0423 (8)0.0422 (8)0.0026 (7)−0.0022 (6)0.0030 (6)
N20.0414 (8)0.0392 (8)0.0450 (8)−0.0028 (6)0.0057 (6)0.0021 (6)
N30.0427 (8)0.0515 (10)0.0389 (8)0.0021 (7)0.0011 (7)0.0071 (7)
N40.0398 (8)0.0387 (8)0.0401 (8)−0.0023 (6)0.0021 (6)0.0007 (6)
O30.0569 (9)0.0816 (12)0.0706 (10)−0.0200 (8)−0.0213 (8)0.0154 (9)
O40.0639 (9)0.0486 (8)0.0622 (9)−0.0070 (7)0.0035 (7)0.0160 (7)
S10.0371 (3)0.0369 (3)0.0455 (3)−0.00028 (17)−0.00039 (19)0.00490 (17)
O110.0530 (8)0.0711 (10)0.0555 (8)0.0094 (8)−0.0120 (7)−0.0037 (7)
O120.0524 (8)0.0540 (9)0.0805 (10)−0.0106 (7)0.0090 (7)0.0128 (8)
O130.0465 (7)0.0392 (7)0.0704 (9)0.0000 (6)−0.0095 (6)0.0100 (6)
O140.0686 (10)0.0524 (9)0.0534 (8)0.0080 (8)0.0123 (7)0.0020 (7)
O1W0.0492 (10)0.0435 (10)0.248 (3)−0.0019 (8)−0.0118 (15)0.0082 (14)
Geometric parameters (Å, º) top
C1—N21.320 (3)C6—H6B0.9600
C1—N11.341 (3)C6—H6C0.9600
C1—H10.9300C7—N41.352 (2)
C2—C71.357 (3)C7—N11.359 (2)
C2—N21.385 (2)C8—N21.468 (2)
C2—C31.427 (3)C8—H8A0.9600
C3—O31.215 (2)C8—H8B0.9600
C3—N31.398 (3)C8—H8C0.9600
C4—O41.212 (2)N1—H1N0.88 (2)
C4—N41.383 (2)S1—O121.430 (1)
C4—N31.390 (3)S1—O111.437 (1)
C5—N31.471 (2)S1—O131.459 (1)
C5—H5A0.9600S1—O141.531 (2)
C5—H5B0.9600O14—H140.88 (3)
C5—H5C0.9600O1W—H1W0.94 (1)
C6—N41.461 (2)O1W—H2W0.94 (1)
C6—H6A0.9600
N2—C1—N1109.47 (16)N2—C8—H8A109.5
N2—C1—H1125.3N2—C8—H8B109.5
N1—C1—H1125.3H8A—C8—H8B109.5
C7—C2—N2106.62 (15)N2—C8—H8C109.5
C7—C2—C3121.88 (17)H8A—C8—H8C109.5
N2—C2—C3131.41 (17)H8B—C8—H8C109.5
O3—C3—N3122.05 (18)C1—N1—C7107.88 (16)
O3—C3—C2126.57 (19)C1—N1—H1N123.5 (15)
N3—C3—C2111.37 (16)C7—N1—H1N128.5 (15)
O4—C4—N4120.96 (18)C1—N2—C2108.04 (15)
O4—C4—N3121.79 (17)C1—N2—C8125.67 (17)
N4—C4—N3117.24 (16)C2—N2—C8126.03 (17)
N3—C5—H5A109.5C4—N3—C3127.13 (16)
N3—C5—H5B109.5C4—N3—C5116.08 (17)
H5A—C5—H5B109.5C3—N3—C5116.73 (17)
N3—C5—H5C109.5C7—N4—C4118.19 (16)
H5A—C5—H5C109.5C7—N4—C6121.72 (16)
H5B—C5—H5C109.5C4—N4—C6119.85 (16)
N4—C6—H6A109.5O12—S1—O11113.08 (10)
N4—C6—H6B109.5O12—S1—O13111.21 (9)
H6A—C6—H6B109.5O11—S1—O13111.21 (9)
N4—C6—H6C109.5O12—S1—O14108.64 (10)
H6A—C6—H6C109.5O11—S1—O14108.70 (9)
H6B—C6—H6C109.5O13—S1—O14103.50 (9)
N4—C7—C2123.95 (17)S1—O14—H14109 (2)
N4—C7—N1128.05 (17)H1W—O1W—H2W95 (3)
C2—C7—N1107.97 (16)
C7—C2—C3—O3174.8 (2)O4—C4—N3—C3179.76 (17)
N2—C2—C3—O3−1.3 (3)N4—C4—N3—C3−1.5 (3)
C7—C2—C3—N3−4.5 (2)O4—C4—N3—C52.6 (3)
N2—C2—C3—N3179.39 (18)N4—C4—N3—C5−178.66 (17)
N2—C2—C7—N4−177.11 (15)O3—C3—N3—C4−176.83 (19)
C3—C2—C7—N45.9 (3)C2—C3—N3—C42.5 (3)
N2—C2—C7—N11.3 (2)O3—C3—N3—C50.3 (3)
C3—C2—C7—N1−175.68 (16)C2—C3—N3—C5179.64 (18)
N2—C1—N1—C71.0 (2)C2—C7—N4—C4−4.5 (3)
N4—C7—N1—C1176.86 (17)N1—C7—N4—C4177.41 (16)
C2—C7—N1—C1−1.4 (2)C2—C7—N4—C6−178.87 (17)
N1—C1—N2—C2−0.2 (2)N1—C7—N4—C63.1 (3)
N1—C1—N2—C8−174.58 (18)O4—C4—N4—C7−179.05 (17)
C7—C2—N2—C1−0.7 (2)N3—C4—N4—C72.2 (2)
C3—C2—N2—C1175.91 (19)O4—C4—N4—C6−4.6 (3)
C7—C2—N2—C8173.66 (17)N3—C4—N4—C6176.66 (16)
C3—C2—N2—C8−9.8 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1N···O13i0.88 (2)1.83 (2)2.709 (2)174 (2)
O14—H14···O1Wii0.88 (3)1.60 (4)2.479 (3)171 (3)
O1W—H1W···O13iii0.94 (1)1.82 (1)2.742 (2)168 (4)
O1W—H2W···O110.94 (1)1.98 (3)2.711 (2)133 (3)
Symmetry codes: (i) −x+1, −y+1, −z+2; (ii) −x, −y+2, −z+2; (iii) −x, −y+1, −z+2.

Experimental details

Crystal data
Chemical formulaC8H11N4O2+·HSO4−·H2O
Mr310.29
Crystal system, space groupMonoclinic, P21/c
Temperature (K)293
a, b, c (Å)9.8296 (10), 6.2879 (6), 21.340 (2)
β (°) 90.788 (2)
V (Å3)1318.8 (2)
Z4
Radiation typeMo Kα
µ (mm−1)0.29
Crystal size (mm)0.21 × 0.18 × 0.13
Data collection
DiffractometerBruker SMART APEX CCD area-detector
diffractometer
Absorption correction–
No. of measured, independent and
observed [I > 2σ(I)] reflections		11981, 2317, 2200
Rint0.020
(sin θ/λ)max (Å−1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.039, 0.111, 1.08
No. of reflections2317
No. of parameters201
No. of restraints3
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3)0.43, −0.38

Computer programs: SMART (Bruker, 2001), SAINT (Bruker, 2001), SHELXTL/PC (Sheldrick, 2008), PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1N···O13i0.88 (2)1.83 (2)2.709 (2)174 (2)
O14—H14···O1Wii0.88 (3)1.60 (4)2.479 (3)171 (3)
O1W—H1W···O13iii0.94 (1)1.82 (1)2.742 (2)168 (4)
O1W—H2W···O110.94 (1)1.98 (3)2.711 (2)133 (3)
Symmetry codes: (i) −x+1, −y+1, −z+2; (ii) −x, −y+2, −z+2; (iii) −x, −y+1, −z+2.
 

Acknowledgements

The authors thank the Vice Chancellor of Anna University of Technology, Tirunelveli, for his support and encouragement.

References

First citationBenowitz, N. L. (1990). Annu. Rev. Med. 41, 277–288.  CrossRef CAS Google Scholar
 First citationBothe, H. & Cammenga, H. K. (1980). Thermochim. Acta, 40, 29–39.  CrossRef CAS Google Scholar
 First citationBruker (2001). SAINT and SMART . Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar
 First citationEdwards, H. G. M., Lawson, E., de Matas, M., Shields, L. & York, P. (1997). J. Chem. Soc. Perkin Trans. 2, pp. 1985–1990.  Google Scholar
 First citationEtter, M. C., MacDonald, J. C. & Bernstein, J. (1990). Acta Cryst. B46, 256–262.  CrossRef CAS Web of Science IUCr Journals Google Scholar
 First citationGriesser, U. J. & Burger, A. (1995). Int. J. Pharm. 120, 83–93.  CrossRef CAS Google Scholar
 First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
 First citationSmith, A. (2002). Food Chem. Toxicol. 40, 9, 1243–1255.  Google Scholar
 First citationSpek, A. L. (2009). Acta Cryst. D65, 148–155.  Web of Science CrossRef CAS IUCr Journals Google Scholar
 First citationSutor, D. J. (1958). Acta Cryst. 11, 453–458.  CSD CAS Google Scholar
 First citationTrask, A. V., Motherwell, W. D. S. & Jones, W. (2005). Cryst. Growth Des. 5, 1013–1021.  Web of Science CSD CrossRef CAS Google Scholar

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ISSN: 2056-9890
Volume 67| Part 9| September 2011| Page o2290
doi:10.1107/S1600536811031540
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